methane uk

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Christian N. Jardine, Brenda Boardman, Ayub Osman
Julia Vowles and Jane Palmer
Environmental Change Institute, University of Oxford
1a Mansfield Road, Oxford OX1 3SZ
Tel: +44 (0)1865 281180
Web: www.eci.ox.ac.uk
email: administrator@eci.ox.ac.uk
methane uk

Objectives
This report forms part of the Biffaward
Programme on Sustainable Resource Use.The aim
of this programme is to provide accessible, well-
researched information about the flows of
different resources through the UK economy
based either singly, or on a combination of
regions, material streams or industry sectors.
Background
Information about material resource flows
through the UK economy is of fundamental
importance to the cost-effective management of
resource flows, especially at the stage when the
resources become ‘waste’.
In order to maximise the Programme’s full
potential, data will be generated and classified in
ways that are both consistent with each other,
and with the methodologies of the other
generators of resource flow/waste management
data.
In addition to the projects having their own
means of dissemination to their own
constituencies, their data and information will be
gathered together in a common format to
facilitate policy making at corporate, regional and
national levels.
Mass balance UK
The methane uk project is not strictly a mass
balance project, as it deals with post-disposal
generation of methane from landfill sites as well
as that from agriculture and fossil fuel sources.
However, it complements existing publications in
the Sustainable Resource Use series including
Carbon UK (2002). More than 30 different mass
balance projects have been funded by Biffaward.
For more information on the Mass Balance UK
programme please visit www.massbalance.org
Acknowledgements
The authors would like to acknowledge the many
helpful discussions held with Mike Mason
(Climate Care), Peter Jones (BIFFA) and Cameron
Davies (Alkane Energy), James Blunt (Spectron)
and Tim Atkinson (Natsource).
Further thanks goes to Deborah Strickland for
her help with the images contained within this
report.
We would also like to recognise our partners
on the www.ch4.org website – Richard Watson,
Catherine Bottrill and Ian Curtis – for their
activities in promoting the links between waste,
energy and climate change.
Biffaward programme on sustainable
resource use

Figures 4
Tables 4
Executive summary 5
1 Methane and climate change
1.1 Climate change and the role of
greenhouse gases 6
1.2 Why methane? 9
1.3 International policy context 10
1.4 UK policy context 12
1.5 Role of methane emissions reductions 12
2 Climate science of methane
2.1 Introduction 14
2.2 Methane sources 14
2.3 Methane sinks 18
2.4 Methane in the atmosphere 20
3 Methane emissions trading
3.1 Emissions trading concept 24
3.2 Emissions trading schemes 26
3.3 Review of the UK ETS 29
3.4 Conclusions 30
4 Methane in the UK
4.1UK methane sources 32
4.2Historical trends 32
4.3Breakdown by region 33
4.4Data uncertainties 34
4.5UK greenhouse gas emissions 35
5Waste and landfill
5.1 Methane from landfill 37
5.2 Landfill in the UK 39
5.3 Methane capture 41
5.4 Alternatives to landfill 45
5.5Recommendations 49
6Agriculture
6.1 How is methane produced? 52
6.2 Mitigating emissions from livestock 53
6.3 Mitigating emissions from manure
management 55
6.4 Existing EU and UK policy 57
6.5 Recommendations 58
7 Oil and gas sector
7.1Introduction 60
7.2 Sources of methane 60
7.3 Mitigating methane emissions 61
7.4Existing UK policies 61
7.5Recommendations 62
8Coal mine methane
8.1 Production 64
8.2 Mitigation 65
8.3 Current policy 68
8.4 Recommendations 69
9 Discussion and conclusions
9.1 Importance of methane 72
9.2 Disparity of methane sources 72
9.3 Methane trading 72
9.4 Recommendations 74
9.5 Conclusions 74
Glossary 78
References 83
Appendix I The atmospheric chemistry
of methane 89
Contents

4
Figure 1 Infra-red radiation is trapped within the
earth’s atmosphere by trace greenhouse gases 9
Figure 2 Global average surface temperature
since 1860 10
Figure 3 Historical and projected atmospheric
concentrations of carbon dioxide 11
Figure 4 Global methane cycle 17
Figure 5 A representative distribution of worldwide
anthropogenic and natural sources of methane 19
Figure 6 Relative concentration of methane in the
atmosphere 22
Figure 7 Radiative forcing of methane and carbon
dioxide 25
Figure 8 Effect of emissions cessation (a) and
gradual reduction (b) on atmospheric
concentration 27
Figure 9 Comparison of (a) regulated approach
& (b) market trading approach 29
Figure 10 UK ETS carbon prices, 2002-4 34
Figure 11 UK sources of methane, 2002 36
Figure 12 Long term trends in methane
emissions, UK 37
Figure 13 Methane emissions by source and
region, 2000 39
Figure 14 UK greenhouse gas emissions, 1990-2002 41
Figure 15 Estimated annual waste by sector
(by mass) 43
Figure 16 Disposal methods of municipal waste,
England, 1996-2003 46
Figure 17 Enteric fermentation in ruminant
mammals 59
Figure 18 Gas consumption by sector, UK,
1970-2003 67
Figure 19 North Sea Oil and Gas Fields 68
Figure 20 Coal fields in the UK 72
Figure 21 Recovery of methane from abandoned
wells 74
Figure 22 Thermal flow reversal reactor 75
Figure 23 Oxidation of methane in the
troposphere 101
Figure 24 Sources and sinks of the hydroxyl radical 102
Table 1 Global Warming Potentials of the
‘basket’ of six gases 11
Table 2 Sources of global methane emissions 16
Table 3 Emissions of methane (Mt) by source as
quantified by different academic studies 17
Table 4 Sinks of methane 21
Table 5 Radiative forcing of selected greenhouse
gases 23
Table 6 Global Warming Potentials for the
greenhouse gas ‘basket’ 25
Table 7 Comparison between the UK and
EU Emissions Trading Schemes 31
Table 8 UK methane emissions from 1990-2002
(Mt CH4) 37
Table 9 Regional breakdown of methane and
total GHG generation, UK, 2000 37
Table 10 UK GHG emissions 1990-2002 (MtCO2e) 39
Table 11 Methane formation in landfill 43
Table 12 The waste hierarchy and options for
dealing with biodegradable matter 45
Table 13 Contracts under Renewables Obligation,
December 2001 50
Table 14 Financial incentives for electricity
generation from waste streams 53
Table 15 Methane produced by enteric
fermentation and manure management
(kg methane per head per year) 57
Table 16 Potential for methane trading in
each sector 80
Table 17 Disparity of methane sources and
appropriate mitigation measures 81
Figures and tables

5
Methane is an extremely powerful greenhouse
gas, particularly in the short-term (less than 12
years). It becomes more long-lived and damaging
as the concentrations in the atmosphere increase,
by altering the balance of the atmospheric
chemical processes. These two important
considerations for methane mitigation policy
indicate that the focus should be on immediate
reductions.
The main sources of methane in the UK related
to human activity are landfill, coal mines,
ruminants and their manure, and leakages from
the natural gas system.
In landfill sites, methane results from the
breakdown of biomass derivatives (e.g. tea leaves,
paper) over a period of at least 15 to 20 years. Up
to 85% of the methane generated can be
captured and then burned to produce electricity
which qualifies for Renewable Obligation
Certificates – an economically profitable process
that provides sufficient incentive to improve
methane capture. The remaining uncaptured
methane will still escape to the atmosphere. The
EU Landfill Directive requires the amount of
biodegradable waste going to landfill in the UK to
be reduced to 35% by 2020, so the quantity of
methane produced will decrease over time.
Coal mine methane comes from both active
and abandoned mines, but only the former is
accounted for in greenhouse gas inventories. The
latter represents a potentially significant figure
that is ignored by the present system although
DEFRA is close to completing an inventory. This
form of methane release should no longer be
ignored. Technologies for capturing methane
from deep mines exist but lack the necessary
financial drivers to encourage implementation in
the UK. There are no current policies to
encourage capture for energy recovery and it is
recommended that these should be developed by
the Government.
There are opportunities to process animal
manure in anaerobic digesters and thus trap the
methane for use in electricity generation that
qualifies for ROCs. This avenue is advocated for
greater encouragement. Policies to reduce the
amount of methane produced by sheep and cows
(the source of 90% of agricultural methane
emissions) – for instance injections, different
feedstocks and preferential breeding – could meet
consumer resistance and are not seen as a
mainstream option. The Common Agricultural
Policy is expected to reduce the present subsidy
(£1.40 per day, per cow), which, along with
consumer trends to less dairy and red meat
consumption, is likely to have a gradual but
persistent effect on UK demand and possibly
production. Agricultural emissions have been
slowly reducing and may continue to do so, but
will remain the major source of methane in the
UK.
The leakage of natural gas from the
transmission and distribution system is poorly
quantified but probably a substantial problem.
Because of uncertainty about the numbers there
can be no possibility of using reductions in a
trading system. The policy emphasis has to be
with Ofgem and regulation.
Methane trading is a viable option for reducing
emissions in some sectors. Methane from active
coal mines and gas and oil rigs has been
successfully traded under the UK Emissions
Trading Scheme. It is essential that this trading
opportunity continues through incorporation of
methane into the EU Emissions Trading Scheme in
2008, with interim policies to cover the two year
gap after closure of the UK ETS in 2006.
These various programmes should be
supported by a more imaginative framework that
reflects the importance of achieving rapid
methane reductions. Serious consideration must
be given to the short-term influence of gases
such as methane. A focus on emissions that have
a strong, immediate effect on the climate would
buy time for carbon dioxide reducing policies and
technologies to become more effective and
prevent methane from becoming more potent.
Executive summary

6 Chapter 1: Methane and climate change
Methane (CH
4
) is a colourless, odourless, tasteless
gas, which is naturally present in the atmosphere
and is the main component of the fossil fuel,
natural gas. The importance of methane (CH
4
) is
second only to carbon dioxide (CO
2
) in terms of
overall contribution to human-induced climate
change. Whilst methane exists in a far lower
atmospheric concentration than carbon dioxide, it
is a particularly powerful greenhouse gas,
deemed responsible for around 20% of post-
industrial global warming.
1
The relative potency
and short atmospheric lifetime of the gas make
efforts to reduce methane emissions an attractive
climate change policy option. A unit reduction of
one tonne of methane is deemed equivalent to a
reduction of 23 tonnes of carbon dioxide.
1
Because of the relative potencies, mitigating
methane emissions is often more cost effective
than mitigating carbon dioxide emissions and is
therefore an ideal method of achieving
international and government set targets at
minimum cost to the economy. It can also buy
time for the development of carbon dioxide
mitigation technologies not sufficiently advanced
at present to be cost-effective.
So far, methane has played a pivotal role in
efforts to meet the UK’s greenhouse gas emission
reduction target under the Kyoto Protocol,
accounting for 30% of the overall greenhouse gas
reduction between 1990 and 2002. However,
much of this decrease in methane emissions has
been serendipitous, being a result of a decline in
the UK coal industry and improved landfill cap
technologies, rather than a result of targeted
policy. In order to help mitigate climate change
and be assured of meeting the Kyoto target and
subsequent obligations, it is imperative that
further methane emission reductions are both
achieved and maintained in the long term.
Identifying the most efficient way of reaching
these goals, coupled with effective policies, must
now be a priority. The question for policy makers
is this – what is the easiest way of reducing our
influence on the climate of our planet with
minimal impact to individuals and minimum
impact to the economy?
This report examines the major sources of
methane in the UK, technologies for emissions
abatement, current policies and future policy
measures that could bring about lasting
emissions reductions, with a particular focus on
the potential for methane trading.
1.1 Climate change and the role of
greenhouse gases
There is now widespread scientific consensus
relating to the profound influence of human
activity on the global climatic system, particularly
through increased emissions of greenhouse gases
in the post-industrial era. The effect on the global
climate is already apparent and is likely to
become more pronounced over the forthcoming
decades.
What is the greenhouse effect?
The greenhouse effect is the term used to
describe the warming mechanism provided by
certain atmospheric gases. These are typically
trace gases, known as greenhouse gases, which
naturally make up about 1% of the atmosphere.
Greenhouse gases are effective absorbers of infra-
red radiation (heat), so the radiation emitted from
the earth’s surface cannot then escape into space
(Figure 1). The net result is that the greenhouse
gases trap energy inside the earth’s atmosphere
and maintain the earth’s surface temperature at
Methane and climate change
Figure 1 : Infra-red
radiation is trapped within
the earth’s atmosphere by
trace greenhouse gases

7 Chapter 1: Methane and climate change
definitive as our current understanding allows.
The IPPC’s Second Assessment Report of 1995
2
was instrumental in the development of the
Kyoto Protocol and the Third Assessment Report
1
was published in 2001.
It is now widely acknowledged that the
delicate natural equilibrium is being thrown out
of balance. The IPPC reports that during the last
century, global average surface temperature has
increased by over 0.6
o
C
1
. This is likely to be the
largest temperature increase of any century
during the last 1000 years and the implications
are becoming increasingly apparent. It is very
likely that the warming during the 20th century
has contributed significantly to the observed sea
level rise of 10 to 20 cm, through thermal
expansion of seawater and widespread loss of
land ice. Since the 1950s, the extent of spring and
summer ice cover in the Northern Hemisphere
has decreased by 10-15% and, since the 1960s,
land snow cover has reduced by around 10%.
Global warming is also linked to marked changes
in precipitation regimes. The intensity and
frequency of droughts in some parts of Asia and
Africa have increased, whilst elsewhere, areas
have become wetter and heavy precipitation
Figure 2 Global average
surface temperature since
1860
Note: Bars are annual average,
solid line is decadal average
Source: IPCC, 2001
1
approximately 30ºC warmer than it would be
were these trace gases not present. As such, the
presence of greenhouse gases in the atmosphere
is vital for our existence. Most notably, they
maintain a moderate temperature where water
can exist in liquid form – an important
precondition for organic life.
The changing global climate
Climate science is extremely complex and whilst
our current understanding is incomplete, it is
advancing as modelling and monitoring improve.
The most accurate picture of our understanding
of the planet’s atmosphere has been achieved
through a ‘consensus’ of current knowledge under
the Intergovernmental Panel on Climate Change
(IPCC). This is a body established by the World
Meteorological Organisation and United Nations
Environment Programme to assess scientific,
technical and socio-economic information
relevant for the understanding of climate change,
its potential impacts and options for adaptation
and mitigation. It does not carry out its own
research but collates information from peer-
reviewed papers into a coherent whole. As such,
the IPCC reports are seen as being as close to

8 Chapter 1: Methane and climate change
events leading to flooding have become more
commonplace.
The IPCC’s Third Assessment Report
2
attributes
‘most’ of the observed warming over the last 50
years to human activity (anthropogenic
emissions) and increased atmospheric
concentrations of greenhouse gases (Figure 3),
leading to an enhanced greenhouse effect.
Continued growth in greenhouse gas
emissions is predicted to intensify climate change
over the next century. In particular, global climate
models predict that average surface temperature
will increase by between 1.4 and 5.8ºC between
1990 and 2100 based on a range of greenhouse
gas emission scenarios. This is far in excess of the
observed changes during the last century and
consequently the knock-on effects for ice
coverage, sea level rise and precipitation regimes
are likely to be intensified.
Global warming and climate change
Climate change is the variability in the earth’s
climate, which is increasing as a result of global
warming. However, the relationship between
global warming and the impacts of climate
change is complex: we cannot say that, for
example in terms of livelihood or economic
impacts, a 4ºC temperature rise will be twice as
harmful as a 2ºC temperature rise.
Some climate impacts are directly related to
the extent of the temperature rise;ice cover will
reduce and sea levels will rise as temperature
increases. For other climate impacts it is the rate
of temperature rise that is the critical factor;
ecosystems are capable of adapting to
temperature rises, but only over suitably long
timescales. The different greenhouse gases have
different potencies and lifetimes and so affect the
extent and rate of global warming in different
ways. Methane is a peculiar case, being potent in
Figure 3 : Historical and
projected atmospheric
concentrations of carbon
dioxide
Source: Global Commons
Institute
Flooding and flood management currently cost the
UK around £2.2 billion per year

9 Chapter 1: Methane and climate change
the short term yet short-lived, therefore
predominantly affecting the short-term rate of
global warming.
1.2 Why methane?
Anthropogenic emissions of greenhouse gases
have caused substantial changes to our climate
and will continue to do so over the course of the
next century and beyond, if emissions are not
stabilised, or preferably reduced.
The IPCC has identified a ‘basket’ of six
greenhouse gases that contribute to
anthropogenic climate change. These are carbon
dioxide (CO
2
), methane (CH
4
), nitrous oxide (N
2
O),
the chlorofluorocarbons (CFCs), perfluorocarbons
(PFCs) and sulphur hexafluoride (SF
6
).
The Kyoto Protocol (Section 1.3) is a multi-gas
abatement strategy, allowing reductions to be
made in any of the six major greenhouse gases.
Such multi-gas strategies have been shown to be
cheaper than a single gas strategy.
3, 4
They are
also politically less sensitive as they allow
countries to choose their own pathway to an
overall greenhouse gas (GHG) emission reduction,
rather than having limits per gas imposed on
them by an external body. This allows flexibility
between different countries with different
portfolios of GHG emissions. For example,
countries with good renewable energy resources
may wish to promote these resources and thereby
reduce carbon dioxide emissions. Other countries
may find it more effective to reduce methane
emissions by altering waste management or
agricultural practices.
Potency
Such multi-gas abatement strategies require a
measure of the relative potency of the different
gases. The Global Warming Potential (GWP) is the
most commonly used parameter for this. Several
different definitions of the GWP exist – by far the
most common is the 100 year GWP, which is used
in all international and government policies
including the Kyoto Protocol (Table 1).
Table 1: Global Warming Potentials of the ‘basket’
of six gases
Global Warming Lifetime
Gas Potential (100-year) (years)
CO
2
1 5-200
CH
4
23 12
N
2
O 296 114
HFCs 12-12,000 0.3 - 260
PFCs 5,700-11,900 2,600-50,000
SF
6
22,200 3,200
Source: IPCC 2001
1
It can be seen that on a 100-year timescale, one
tonne of methane is 23 times more potent than
one tonne of carbon dioxide. This makes
methane an attractive option for greenhouse gas
emission reductions because smaller reductions
are necessary to achieve the same environmental
goal. Methane is currently emitted in enough
volume to make any reductions significant in
terms of the overall GHG picture. Methane can be
readily captured from localised sources such as
landfill and coal mines. Furthermore, methane is
a flammable gas with a high energy content
which, once captured, can be used as a fuel with
the added economic benefits of heat or electricity
generation.
True potential
The Third Assessment Report provided revised
GWP figures for a number of gases, notably
increasing the relative potency of methane from
21, quoted in the Second Assessment Report, to 23.
However, parties to the UNFCCC have agreed that
the revised figures will not apply until the second
commitment period (2013-2017). Therefore
progress towards the original Kyoto targets set
for 2008-2012 will continue to be calculated using
GWP figures provided within the Second
Assessment Report (i.e. a GWP of 21). Similarly,
inventory submissions will continue to be based
on old GWP figures throughout this period,
according to the current reporting guidelines.
5

10 Chapter 1: Methane and climate change
For the remainder of this report, a GWP of 23 is
used when referring to the current level of
scientific understanding. However, a GWP of 21 is
implied in all discussions relating to current policy
concerned with emissions as reported under the
UN Framework Convention on Climate Change
guidelines (Section 1.3).
Lifetime
It is also worth noting that methane has a
comparatively short lifetime in the atmosphere of
just 12 years, compared with up to 200 years for
carbon dioxide. This means that reductions in
emissions are rapidly turned into atmospheric
concentration reductions. Gases with a longer
lifetime reach higher atmospheric concentrations
and experience a longer lag between emissions
reductions and decreased atmospheric
concentrations. Reducing emissions of short-
lifetime potent gases such as methane is
therefore a valuable means of rapidly slowing
global temperature rise. This gives reduction of
methane emissions a high economic value
(perhaps even greater than reflected in the GWP
of 23) as they are effective at slowing the rate of
global warming. They are also likely to be even
more important at some point in the future
should the effects of climate change become
critical and fast-acting measures need to be
adopted.
6, 7
1.3 International policy context
The international community originally drew
attention to the link between climate change and
human activities at First World Climate
Conference in 1979. Extensive scientific research,
international debate and a series of
intergovernmental conferences followed,
culminating in 1992 with the production of the
UN Framework Convention on Climate Change
(UNFCCC).
The UN Framework Convention on Climate
Change
The UNFCCC entered into force in 1994. Currently
181 governments and the European Union are
party to the Convention. Its ‘ultimate objective’ is
to stabilise atmospheric concentrations of
greenhouse gases at safe levels, although it does
not assess what these levels are. The signatories
are required to submit regular national
communications, including information on
strategies for mitigating and adapting to climate
change along with detailed greenhouse gas
emission inventories.
The atmospheric concentration of any
greenhouse gas is determined by the balance
between emissions from sources of the gas and
removals by sinks. At present, emission rates
exceed rates of removal and consequently
atmospheric concentrations of greenhouse gases
continue to rise. The IPCC report that in order to
stabilise carbon dioxide emissions at 450, 650 or
1000 ppm, global anthropogenic emissions would
need to drop below 1990 levels within a few
decades, about a century, or about two centuries,
respectively, and continue to decrease steadily
thereafter.
Even if emissions are stabilised now, global
average surface temperature is expected to
continue to rise for centuries to come. However,
by stabilising emissions as quickly as possible, the
temperature increase could be reduced from
several degrees per century to tenths of a degree.
The lower the level at which emissions are
stabilised, the smaller the increase in temperature
expected. Furthermore, by acting on the more
short-lived methane, the global temperature
increase can be minimised more rapidly.
The Kyoto Protocol
The ultimate goal of the UNFCCC is the
“stabilisation of greenhouse gas concentrations in
the atmosphere at a level that would prevent
dangerous anthropogenic interference with the
climate system”. In 1997, the adoption of the
Kyoto Protocol went one step further towards this

11 Chapter 1: Methane and climate change
goal, strengthening the commitments under the
UNFCCC by providing legally binding emission
reduction targets for developed countries (the
so-called Annex I countries). Targets for individual
countries were established through negotiation,
although in total are equivalent to a 5.2%
reduction from 1990 levels by the first
commitment period of 2010 (defined as the
average emissions for the period 2008-2012, to
cope with anomalous years).
It is widely acknowledged that these 5.2%
targets set by the Kyoto Protocol are not stringent
enough to avert potentially catastrophic climate
change, but they are a major step in the right
direction. Crucially, it is envisaged that the Kyoto
Protocol will entail further five-year commitment
periods, with progressively stricter emission
reduction targets. The second commitment period
is scheduled for 2013-2017, with negotiations of
targets beginning in 2005.
The Kyoto Protocol will finally become legally
binding on 16 February 2005, following
ratification of the treaty by Russia in November
2004.
How will the Kyoto Protocol work?
To alleviate the adverse economic effects of
comprehensive limits on greenhouse gas
emissions, three flexibility mechanisms, also
referred to as the Kyoto mechanisms, were
included in the Kyoto Protocol: International
Emissions Trading (IET), Joint Implementation (JI)
and the Clean Development Mechanism (CDM).
The purpose of these mechanisms is to allow
industrialised countries to meet their targets
through trading emission allowances with each
other and gaining credits for emission-curbing
projects abroad.
The central strategy to curb greenhouse gas
emissions is that of emissions trading through
the IET. Emissions trading involves the trading of
permits to emit greenhouse as if they were
conventional commodities such as gold or oil. It
allows emissions reductions to be achieved at
minimal cost to the economy, by allowing over-
emission from those who cannot meet targets
cheaply to be offset by under-emission from
those who can mitigate at low cost. Emissions
trading, and the role that methane might play
within such a scheme, is discussed in greater
detail in Chapter 3. While implementation of the
three flexibility mechanisms at international level
will become possible only once the Kyoto Protocol
comes into force, emissions trading of greenhouse
gases has already begun at a domestic level in the
UK and in other countries such as Denmark. The
EU has already put in place an EU-wide trading
scheme, due to start in 2005.
Joint Implementation and the Clean
Development Mechanism are designed to provide
flexibility for countries to meet part of their Kyoto
targets by taking advantage of opportunities to
reduce greenhouse gas emissions in other
countries at lower cost than at home. These two
mechanisms are project-based and allow the
generation of credits when projects achieve
emission reductions that are additional to that
which would have occurred in the absence of the
project. Joint Implementation refers to projects in
countries that also have emission targets,
whereas the Clean Development Mechanism
refers to projects in developing countries with no
targets. The rationale is that, for the global
environment, where the emission reduction
occurs is of secondary importance provided that
real emission reductions are achieved. In order to
promote participation by corporate investors, this
should be allowed to occur where costs are
lowest.
Renewable energy
currently accounts for
around 3% of UK
electricity generation

12 Chapter 1: Methane and climate change
Addressing climate change in the UK
The UK was amongst the first nations to ratify
the Kyoto Protocol. Under burden sharing
agreements within the EU, the UK has committed
to an emissions reduction target of 12.5%, relative
to a 1990 baseline, on the ‘basket’ of six
greenhouse gases by 2008-2012. This target can
be met through reductions in all or any of the
basket of six gases, allowing flexibility in the
choice of policy options, and is calculated in CO2
equivalent terms.
The Energy White Paper, published in February
2003, has positioned the UK at the forefront of
international efforts to tackle climate change,
with an ambitious target of a 60% reduction in
carbon dioxide emissions by 2050.
8
The UK
Government is working to encourage the
international community to adopt similar targets
with the launch of its International Energy
Strategy in October 2004.
9
1.4 UK policy context
There are certain UK policies which have played a
role in encouraging methane emissions
reductions, either directly or indirectly.
Renewables targets
Under the EU Renewables Directive, which came
into force in October 2001, the UK has adopted a
target of 10% of UK electricity consumption by
2010 to come from renewable sources. In
previous years wastes have been included with
renewables, but from 2004, the international
definition of total renewables has been adopted
which excludes non-biodegradable wastes.
10
Renewables Obligation
The Renewables Obligation, introduced in April
2002, is the key policy measure to help achieve
the UK’s renewable energy targets and will
remain in place until 2027, with yearly targets set
up until 2011. It requires all licensed electricity
suppliers in England and Wales to supply a
specific proportion of their electricity from
renewables, evidenced via a system of
Renewables Obligation Certificates (ROCs).
ROCs are issued to accredited generators and
may be traded separately from the electricity to
which they relate, allowing suppliers who have
failed to reach the target to purchase certificates
from those suppliers that have surpassed their
Obligation requirements. Renewable
technologies eligible for ROCs include wind,
landfill gas and incineration of biomass, amongst
others. Incineration and co-firing of mixed waste
are excluded. ROCs are one of the key economic
drivers in the UK for encouraging investment in
methane mitigation.
Climate Change Levy
The Climate Change Levy (CCL) was introduced in
April 2001 as a tax on electricity supplied to non-
domestic customers in the UK. Intensive users of
energy are able to join Climate Change Levy
Agreements, helping to mitigate the effects of
this tax. Under these agreements, businesses
that accept and subsequently meet energy
reduction targets will receive an 80% levy
discount until the year 2013. Electricity from
qualifying renewable sources, such as solar and
wind power, is exempt from the Levy and eligible
for Levy Exemption Certificates (LECs). Electricity
from some energy from waste schemes is not
exempt.
1.5 Role of methane emissions
reductions
The importance of methane in meeting the UK’s
Kyoto target cannot be understated. So far,
methane emissions have fallen by 43% between
1990 and 2002 (Section 4.5), equivalent to 30% of
the UK’s total greenhouse gas emission
reductions. The proportional contribution of
methane to total emission reductions is expected
to increase, with UK Government baseline

13 Chapter 1: Methane and climate change
projections aimed at halving methane emissions
by 2020.
11
Emphasis on methane emission reduction
could pave the way for commercial opportunities
and enhanced competitiveness, with increased
efficiency and technological developments in
methane mitigation, capture and utilization
forming an integral component of a lower carbon
economy. Methane emission reduction is also
particularly apposite to improved safety, owing to
the flammable and explosive nature of the gas.
Furthermore, the high energy content of methane
makes its combustion for energy recovery highly
desirable. Utilisation of methane to generate
electricity or heat, producing the less potent
carbon dioxide, can offset emissions from more
carbon-intensive coal or oil powered generators.
On a global basis, the benefits of methane
emission reductions in terms of climate change
abatement may be even more profound. The short
lifetime and relative potency of methane in the
atmosphere mean that the benefits of emission
reductions are quickly apparent. Investment in
methane abatement technologies would buy
time for the development of cheaper carbon
dioxide mitigation technologies, especially new
renewable energy technologies. Large cuts in
methane emissions could potentially avert or
delay climate change in the short term, providing
the much needed time for carbon dioxide
mitigation policies to be implemented and their
effects observed in the atmosphere.

2.1 Introduction
Methane is the most abundant reactive trace gas
in the atmosphere and arises from both natural
and anthropogenic sources. It is a valuable gas
and is usable at a wide range of concentrations,
down to 5%. In concentrated form it is flammable,
representing an explosion risk in confined
conditions.
The global atmospheric burden of methane (in
1998) was 4850 Mt(CH
4
), equivalent to an average
concentration of 1745 parts per billion (ppb). The
global methane budget can be modelled by
simply considering emissions as increasing the
atmospheric burden of methane, with sinks
removing methane from the atmosphere – the
methane cycle. The concentration of methane in
the atmosphere is thought to be increasing at a
rate of 22 Mt/yr, due to the imbalance between
estimated annual global emissions of 598 Mt and
removals of 576 Mt (Figure 4).
1
It is therefore important to reduce global
emissions to such a level that they are
outweighed by methane sinks, so that the
concentration of methane in the atmosphere
decreases and its subsequent warming effect is
reduced. A reduction of global emissions by just
22 Mt per year would result in stabilisation of
methane concentrations in the atmosphere. Such
a reduction represents just 3.6% of total methane
emissions, or 6.1% of anthropogenic emissions.
Such small reductions should be attainable.
Obtaining a reduction in atmospheric methane
concentrations would provide an encouraging
example in the fight against global warming.
14 Chapter 2: Climate science of methane
2.2 Methane sources
Methane is emitted from a range of natural and
anthropogenic (relating to human activity)
sources as a result of the anaerobic
decomposition of organic matter, land use
changes and fossil fuel related emissions (Table 2).
Table 2: Sources of global methane emissions
Natural Anthropogenic
Wetlands Agricultural livestock
Termite activity Rice cultivation
Oceans Waste practices
Coal mining
Natural gas distribution
Biomass burning
Whilst the major sources of atmospheric methane
have been identified, quantifying their individual
contributions to global emissions has proved
Climate science of methane
Figure 4: Global methane cycle
Wetlands are areas of marsh, fen, peatland and
water, representing approximately 6% of the
world’s land surface

15 Chapter 2: Climate science of methane
problematic.
12, 13
For many sources, emissions are
highly variable in space and time. For instance,
emissions from most types of wetlands can vary
by a few orders of magnitude over just a few
metres.
1
Based on a range of studies, the IPCC
1
estimates that global emissions of methane are
around 598 Mt per year, but does not provide a
definitive breakdown of CH
4
emissions by source.
Other studies have attempted to classify this, but
there are a wide range of estimates and
definitions used for each sector (Table 3). This lack
of accuracy and definitive emissions figures is a
serious handicap to the design of practical policy
and trading schemes.
13
Table 3: Emissions of methane (Mt) by source as quantified by different academic studies
Source Fung Hein Lelieveld HouwelingMosier Olivier Cao
et al.
14
et al.
15
et al.
16
et al.
17
et al.
18
et al.
19
et al.
20
SAR
2
TAR
1
Natural
Wetlands 115 237 225 145 92
Termites 20 20 20
Ocean 10 15 15
Hydrates 5 10
Anthropogenic
Energy 75 97 110 89 109
Landfill 40 35 40 73 36
Ruminants 80 90 115 93 80 93
Waste Treatment 25 14
Rice Agriculture 100 88 25-54 60 53
Biomass 55 40 40 40 34 23
Other 20 15
TOTAL 500 587 600 597 598
Source: IPCC, 2001
1
The role of bacteria
There are two classes of bacteria actively involved
in the methane cycle. Methanogenic bacteria
generate methane by breaking down organic
matter in the absence of oxygen (anaerobically),
releasing carbon dioxide and methane according
to the reaction:
Bacterial
Action
C
6
H
12
O
6
(e.g. cellulose)
3CO
2
+ 3CH
4
Conversely, methanotrophic bacteria oxidise
methane to carbon dioxide. Methanotrophic
bacteria are of two sorts; low affinity oxidation,
where methanotrophs oxidise high
concentrations of methane at the source of
production (usually a population of
methanogenic bacteria), and high affinity
oxidation, which can oxidise methane present at
atmospheric concentrations.

16 Chapter 2: Climate science of methane
Natural sources
The main natural sources of methane are
wetlands, termites and oceans. Wetlands are by
far the largest source, accounting for 30% of total
emissions (Figure 5), with methane being
produced from the anaerobic decomposition of
organic matter covered by water. Because this
process involves the action of bacteria, the rate of
methane production is strongly temperature
dependent. Maximum methane production is
experienced at temperatures between 37 and
45ºC and so future increases in global
temperature may enhance methane production
from wetlands, thereby reinforcing the
greenhouse effect.
Methane is also produced by the digestive
processes of termites, resulting in the generation
of around 20 Mt per year – approximately 5% of
world methane emissions. This value is unlikely
to change as termite populations are not
expanding despite greater availability of biomass
due to deforestation.
22
Methane emissions from
termites should be treated as a significant, but
background, source that is likely to remain
constant.
Oceans contribute approximately 2% to global
methane emissions. The methane is produced by
methanogenic bacteria within sinking particles in
surface waters. The production of methane from
oceans is spatially dependent, with much
methane arising from methanogenesis in marine
sediments, particularly in nutrient rich areas such
as estuaries. There is also an anthropogenic
component to ocean emissions, with bacterial
populations being increased by high nutrient
levels from agricultural fertiliser run-off and
waste treatment effluents.
Anthropogenic sources
Approximately 60% of emissions are related to
human activities. The key anthropogenic sources
of methane include fossil fuels, agriculture,
landfill and the burning of biomass. Methane
emissions arising from the fossil fuel industry
form the largest anthropogenic source of
methane, estimated to be between 80 and 100
Mt per year. The main sources of fossil fuel-
related methane emissions are the release of
natural gas from coal mining and leakage from
gas processing and distribution pipes. Pockets of
methane that have been trapped between layers
of coal during its formation and methane within
the coal itself are released once the coal is mined.
Agricultural practices also result in significant
methane emissions, the two major sectors being
rice production and the rearing of livestock.
Paddy fields for rice production are essentially
man-made wetland areas and are characterised
by high moisture content, oxygen depletion and
high organic substrate and nutrient levels.
23
As
such, they provide ideal conditions for
methanogenic bacteria and result in substantial
emissions of methane of approximately 40 Mt
per year. Up to 90% of this methane is absorbed
by populations of methanotrophic bacteria, which
convert the methane to carbon dioxide, but the
remaining 10% escapes to the atmosphere. The
production of 1 kg of rice corresponds to the
emission of 100 g of methane.
24
It is worth
noting that the accuracy of methane emissions
estimates has improved substantially over the
past decade, with current figures almost half
previous estimates.
1
Figure 5: A representative distribution of worldwide anthropogenic and natural
sources of methane
Source: Khalil, 2000
21

17 Chapter 2: Climate science of methane
Methane is produced as part of the natural
digestive processes of ruminant animals such as
cattle, sheep and goats. Food is broken down by
bacteria in the rumen, aiding digestion, since
stomach enzymes are insufficient to break down
plant polymers. However, the action of these
bacteria yields methane, carbon dioxide and
ammonia as gaseous by-products. With an
increasing global population, coupled with higher
living standards, livestock numbers are increasing
world-wide and contribute some 50-100 Mt per
year to global methane emissions.
Landfill sites also provide an anaerobic
environment where methanogenic bacteria break
down waste organic materials. Somewhere
between 40 and 60% of landfill gas is methane,
depending on the composition of the waste. The
remainder is mainly carbon dioxide with other
trace gases. The amount of methane emitted to
the atmosphere from a landfill site is strongly
dependent on the design and operation of the
site. Unchecked, the landfill gas will simply
permeate through the waste or along cracks in
the compacted waste or bedrock. Modern landfill
sites use impermeable liners and a capping layer
to control the movement of the gas, which may
then be collected. However, even the best caps
are only 85% efficient
25
with the remaining 15% of
methane escaping through the cap.
26
This is
offset by breakdown of up to 90% of the
methane in the capping layer by methanotrophic
bacteria (Section 5.1).
The burning of biomass releases around 40 Mt
of methane into the atmosphere each year.
Biomass burning results mainly in the production
of carbon dioxide, but if fires smoulder and
combustion is incomplete, methane and other
volatile organic compounds are released. The
extent of methane emissions is dependent on the
completeness of combustion and the carbon
content of the fuel used.
27
Methane hydrates
Although currently neither a source nor a sink,
methane hydrates are by far the largest store of
methane on the planet and account for 53% of all
fossil fuels on earth.
28
They are a crystalline solid
mixture of water and methane (essentially
methane trapped in ice) and are found in ocean
floor sediments and arctic permafrost. Methane
hydrates are stable compounds and are not part
of the methane cycle described in this chapter.
The methane in ocean sediment hydrates is
trapped by the high pressure deep in the ocean
but is released above a depth of 400m as the
pressure drops. The energy industry is keen to
take advantage of this and mine these deposits.
29
Methane contained in arctic tundra, trapped
within the frozen solid structure of the hydrate, is
a more serious issue. Should temperatures rise,
the methane hydrate will melt, releasing methane
gas to the atmosphere. There is concern that, if
rising global temperatures due to anthropogenic
climate change cause the arctic permafrost to
melt, massive quantities of methane would be
released into the atmosphere, causing a
catastrophic run-away greenhouse effect beyond
even the upper 5.8ºC estimate postulated by the
IPCC. Such a process is believed to have occurred
in the Palaeocene-Eocene Thermal Maximum,
30
some 55 million years ago, when average global
temperatures increased by 5ºC and which lasted
for 150,000 years.
Is it renewable?
The question of whether methane is a renewable
resource is central to determining its eligibility for
strong financial incentives such as ROCs.
Renewable energy technologies are defined as
Rice paddy soil is fully
waterlogged for 4 months
each year, creating an
artificial wetland

18 Chapter 2: Climate science of methane
relying on “natural energy flows and sources in
the environment, which, since they are
continually replenished, will never run out”.
31
Agricultural emissions, being biogenic are
clearly renewable. Methane from landfill is
mostly derived from decomposition of plant-
based material and once flared is approximately
carbon neutral.
32
It is also arguable whether
waste streams are a ‘natural flow’, but it is
assumed that societies will always produce some
waste as a consequence of their activities.
Landfill gas is therefore defined as a renewable
resource. However, if the same waste stream is
combusted to generate electricity, this does not
count as renewable because fossil-fuel based
plastics are incinerated.
Coal mine methane is certainly an energy flow
within the environment, but is it a natural flow?
As a resource, methane would not be released to
the atmosphere were it not for human action,
although the same could be argued for landfill
gas, which does qualify for ROCs. However,
landfill gas is carbon-neutral, whereas the release
of coal mine methane must be considered an
addition to the present carbon cycle. The DTI does
not consider coal mine methane to be a
renewable resource.
33
Methane from the oil and
gas industries is also considered non renewable.
Although the issue of what is classified as
renewable is not straightforward, especially when
considering landfill and coal mine methane, the
separation assumed by policy makers is clear. If
the methane is generated from biogenic sources,
it is renewable. Conversely, if it is derived from
fossil fuel sources, it does not count as renewable.
Future outlook
Both natural and anthropogenic sources of
methane are likely to change the atmospheric
burden over the forthcoming century.
1
There is
considerable potential to reduce the
anthropogenic sources of methane by improved
waste management and changes in agricultural
practice. However, these sectors are still prone to
upward pressure due to an increasing global
population with increasing energy, land and
dietary demands. Natural emissions may also
increase further as a result of global warming, as
higher average global temperatures may
stimulate microbial activity.
2, 20
2.3 Methane sinks
Methane is removed from the atmosphere (i.e.
converted to less harmful products) by a range of
chemical and biological processes, which occur in
different regions of the atmosphere. These
include tropospheric oxidation, stratospheric
oxidation and uptake by soils.
The troposphere is the lowest 15 km of the
atmosphere. As colder air lies on top of warmer
air in this section of the atmosphere, the
troposphere is well mixed vertically by convection
currents. The methane is therefore present at a
constant concentration of approximately 1.7 ppm
throughout the troposphere. Because
atmosphere decreases in density with increasing
altitude, over 75% of the atmosphere, and
therefore by far the majority of methane, is
contained within the troposphere (Figure 6).
Oxidation of methane in the troposphere is the
Flaming ice: methane
hydrates are essentially
methane trapped in ice

19 Chapter 2: Climate science of methane
largest methane sink, removing 506 Mt of
methane per year from the global methane
burden (Table 4). It is therefore changes to the
chemistry and composition of the troposphere
that will dominate the future environmental
impact of methane emissions.
Above the troposphere lies the stratosphere.
The stratosphere is less dense than the
troposphere and is not mixed vertically by
convection, as warmer air lies on top of colder air
in this region. Methane enters the stratosphere
from below and is consumed by chemical
reactions, so the relative concentration of
methane decreases with altitude. Stratospheric
oxidation of methane consumes 40 Mt per year.
The third process for removal of methane from
the atmosphere occurs at the ground-atmosphere
interface. Bacteria present in soils can also
oxidise methane, thereby removing it from the
atmosphere.
Table 4: Sinks of methane
Mechanism Methane removal (Mt)
Tropospheric oxidation 506
Stratospheric oxidation 40
Soil uptake 30
Total 576
Emissions 598
Tropospheric oxidation
The predominant mechanism for removal of
methane from the earth’s atmosphere is
oxidation within the troposphere by the hydroxyl
radical (OH). The hydroxyl radical is responsible
for the breakdown and removal of a host of trace
gases, including methane, and for this reason is
known as the ‘cleanser of the atmosphere’. In
essence, atmospheric OH effects a low-
temperature combustion of ‘fuels’, such as
methane and other hydrocarbon species, by
eventually oxidising methane to carbon dioxide,
as would happen if methane were burned.
Reactions between methane and the hydroxyl
radical initiates a chain of possible reactions that
produce other species, such as carbon monoxide,
nitrogen dioxide and hydroperoxide, which can
then be removed from the atmosphere. This is a
complex process with numerous feedback loops.
A more detailed discussion of these reactions is
provided in Appendix I.
The overall rate of removal of methane is
dependent on the rate of the initial reaction
between methane and hydroxyl. This, in turn, is
dependent on the concentrations of these species
in the atmosphere. This has two important
consequences.
•Reaction between methane and hydroxyl
removes both species from the atmosphere. As
the concentration of hydroxyl reduces, the rate
of methane removal will slow down. Increasing
atmospheric methane concentrations removes
hydroxyl from the atmosphere and so slows its
own removal.
• Because the hydroxyl radical - the cleanser of
the atmosphere - is capable of reacting with
many species, methane is not the only
influence on its concentration. Sources of
hydroxyl (mainly ozone) are roughly constant,
but it may be removed from the atmosphere by
reactions with carbon monoxide (CO), nitrogen
dioxide (NO
2
), hydroperoxide (HO
2
) and volatile
organic compounds. In particular, the reaction
between carbon monoxide and hydroxyl
proceeds very rapidly, so carbon monoxide
Figure 6: Relative concentration of methane in the
atmosphere
Source:Warneck, 1988
34

20 Chapter 2: Climate science of methane
scavenges hydroxyl from the atmosphere.
Increased anthropogenic emissions of carbon
monoxide (from transport), coupled with the
further carbon monoxide produced from
oxidation of methane, can cause significant
hydroxyl concentration reductions and so slow
the rate of methane removal.
As the rate of methane removal slows, its lifetime
in the atmosphere and therefore its GWP will
increase. Methane will become a more potent
greenhouse gas over time if hydroxyl
concentrations continue to decrease. In terms of
policy, it is more effective to reduce methane
emissions now while hydroxyl concentrations
remain relatively high. Delaying action to reduce
methane emissions, until a time when hydroxyl
concentrations are lower, will result in the
emitted methane being more potent.
Furthermore, successful methane emission
reductions, preferably accompanied by lower
anthropogenic carbon monoxide emissions, could
result in an increase in hydroxyl concentrations
and a subsequent lowering of the GWP of future
methane emissions. This beneficial positive
feedback loop is a further reason for encouraging
methane emissions reduction in the short term.
Stratospheric oxidation
Some of the methane present in the troposphere
passes into the stratosphere. Approximately 40
Mt of methane are oxidised in the stratosphere,
representing 7% of all methane removal. The
chemistry of methane in the lower stratosphere is
identical to that in the troposphere, with hydroxyl
radicals oxidising methane in the same manner.
Indeed, oxidation of methane to carbon dioxide
and water is the source of approximately 50% of
stratospheric water vapour.
In the upper stratosphere, methane
decomposition can be initiated in two other ways:
by reaction with chlorine radicals or oxygen
atoms. Chlorine atoms are produced by
decomposition of CFCs and related compounds by
the high intensities of ultraviolet light found in
the upper stratosphere. Oxygen atoms are
similarly produced by the decomposition of ozone
(O
3
) in uv light; it is this reaction in the ‘ozone
layer’ that prevents harmful ultraviolet radiation
reaching the earth’s surface.
When chlorine or oxygen atoms react with
methane, they initiate the same chain reactions
that occur in the troposphere, resulting in overall
oxidation of methane and removal from the
atmosphere.
Uptake by soils
Approximately 30 Mt of methane are removed
from the atmosphere annually by uptake in soils.
Soils contain populations of methanotrophic
bacteria that can oxidise methane, by a process
known as ‘high affinity oxidation’. These bacteria
consume methane that is in low concentrations,
close to that of the atmosphere (<12 ppm). The
bacteria favour upland soils, in particular forest
soils.
24
Surprisingly, the bacteria responsible for
high affinity oxidation processes remain largely
unidentified. It is known, however, that exposure
of soils to high ammonium concentrations leads
to a loss of methanotrophic bacteria and a
subsequent reduction in the rate of methane
oxidation. The use of artificial fertilisers
containing ammonia is therefore detrimental to
the removal of methane.
24
2.4 Methane in the atmosphere
The atmospheric concentration of methane is
thought to have increased by a factor of 2.5 since
pre-industrial times, reaching 1745 ppb in 1998.
1
This rate of increase far exceeds that of carbon
dioxide, concentrations of which are only 30%
higher than in pre-industrial times. In fact,
information is sufficient for the IPCC to assert
that the current methane concentration has not
been exceeded in the last 420,000 years.
1

21 Chapter 2: Climate science of methane
forcing of methane is 0.48 W/m
2
.Itis important
to note that this is not the radiation absorbed by
the 1745 ppb methane in the atmosphere. Rather
it is the radiative forcing of the extra 1045 ppb
methane present in the atmosphere since 1750.
Essentially the radiative forcing is the difference
in rate of heat capture now versus then.
Table 5: Radiative forcing of selected greenhouse
gases
CO
2
CH
4
N
2
O
Pre-industrial
concentration
(ca. 1750) ppb 280,000 700 270
Concentration in
1998 (ppb) 365,000 1745 314
Relative
concentration
1998/1750 1.30 2.49 1.16
Radiative forcing
(W/m
2
)1.460.48 0.15
Atmospheric
lifetime (years) 5-200 12 114
Source: IPCC, 2001
1
From Table 5, it can be seen that carbon dioxide is
the most important greenhouse gas, with a
radiative forcing of 1.46 W/m
2
. Methane is the
second most important anthropogenic
greenhouse gas, contributing 20% to the total
radiative forcing, proportionally far greater than
expected according to atmospheric
concentrations of the gases. The explanation lies
in the considerable potency of methane as a
greenhouse gas.
Global Warming Potential
The different greenhouse gases vary in both
potency and their lifetime within the atmosphere.
On emission, different greenhouse gases have
different abilities to absorb radiation. However,
the radiative forcing of the emitted gas decays
exponentially as the gas is removed from the
atmosphere over time and the concentration
Ecosystems may not be
able to adapt to a rapid
rate of climate change
How much heat is being trapped?
The amount of ‘extra’ energy being held within
the earth’s atmosphere because of the rise in
atmospheric GHG concentrations is termed
radiative forcing, measured in units of watts per
metre square (W/m
2
). Radiative forcing is the
change in radiation balance due to a change in
greenhouse gas concentrations over a quoted
timeframe. The total radiative forcing of the well-
mixed greenhouse gases since pre-industrial
times (1750) is 2.43 W/m
2
.Of this, the radiative

22 Chapter 2: Climate science of methane
decreases (Figure 7). The rate of this removal is
dependent on the atmospheric lifetime of the
species involved. It is therefore difficult to
determine an absolute measure of the relative
effects of one tonne of each gas, because these
will vary over time. In fact, it is impossible to
combine the two influences of potency and
lifetime into a single definitive figure that reflects
the properties of a greenhouse gas. However, it is
useful to have one single parameter that reflects
the influence of different gases, especially under
multi-gas abatement schemes such as the Kyoto
Protocol and other emissions trading schemes.
The Global Warming Potential (GWP) is the
parameter that has been adopted.
The GWP of a greenhouse gas is defined as
“the [cumulative] radiative forcing from the
instantaneous release of 1 kg of a trace substance
relative to that of 1 kg of a reference gas”.
1
The
reference gas is almost always carbon dioxide and
so its GWP is always unity (Table 6). In visual
terms, this is the relative area under the curves in
Figure 7, up to a certain time limit. Short-lived
gases such as methane have higher GWPs under
short time-horizons. Conversely, long-lived
species such as SF
6
have higher GWPs under long
time-horizons. Table 6 shows the Global Warming
Potential of the basket of six greenhouse gases
over three different timeframes.
The effect of different time horizons poses
interesting questions with regards to policy.
Which value of GWP should be used to assess the
relative importance of methane emissions versus
carbon dioxide? The Kyoto Protocol and other key
policies use the 100-year time horizon, although
these are currently based on the old GWP for
methane of 21 given in the IPCC’s Second
Assessment Report. This will be updated to 23 for
the second commitment period (2013-17). The
IPCC most frequently quotes the 100-year GWPs,
although has made no policy recommendations
as to which GWP timescale to use.
Calculating CO
2
equivalent emissions
It proves useful to measure the potency of
greenhouse gas emissions in one set of units:
tonnes CO
2
equivalents (t CO
2
e). To calculate the
impact of methane emissions, the mass emitted
is multiplied by the 100-year GWP. One tonne of
methane is deemed equivalent to 23 t CO
2
e.
It is also important to note that GWP is
defined in terms of mass of emitted gas, not
volume. Care must be taken if GHG emissions are
measured as volumes – one litre of carbon dioxide
weighs 2.75 times as much as one litre of
methane. So one litre of methane is 8.4 times
(23/2.75) as potent as one litre of carbon dioxide.
Figure 7: Radiative forcing of methane and carbon dioxide
Table 6: Global Warming Potentials for the greenhouse gas ‘basket’
Global Warming Potential
Lifetime (time horizon in years)
Gas (years) 20 years 100 years 500 years
CO
2
5-200 1 1 1
CH
4
12 62 23 7
N
2
O 114 275 296 156
HFCs 0.3-260 40-9,400 12-12,000 4-10,000
PFCs 2,600-50,000 3,900-8,000 5,700-11,900 8,900-18,000
SF
6
3,200 15,100 22,200 32,400
Source: adapted from Table 3, IPCC 2001
1

23 Chapter 2: Climate science of methane
The influence of lifetime
The Global Atmospheric Lifetime of methane in
the atmosphere is defined as the atmospheric
burden (concentration) divided by the sink
strength (annual removal).
However, the chemistry of methane in the
atmosphere contains several feedback loops
affecting the concentration of other atmospheric
species such as O
3
and OH, which slows the
removal of GHGs (including methane itself) from
the atmosphere. This feedback effect is included
in the Perturbation Lifetime, which is longer than
the Global Atmospheric Lifetime and is equal to 12
years. The Perturbation Lifetime is the standard
figure used.
For constant emissions, species with a short
lifetime do not reach such high atmospheric
concentrations because they can be removed
more rapidly from the atmosphere. If emissions
===8.4 years
Global Atmospheric
Lifetime of CH
4
Atmospheric burden
Sink strength
4850 Mt
576 Mt
are stopped completely, as shown in Figure 8a, the
atmospheric concentration of a short lifetime gas
will drop away much more rapidly than a gas with
a long lifetime.
A sudden stop in emissions of a particular gas
is an unlikely scenario, so Figure 8b looks at the
effect of gradually reducing emissions over a
period of time. It can be seen that the
concentration of the short lifetime gas reaches its
peak earlier and also drops away more rapidly
after this point. This means that policies
targeting short-lived gases, such as methane, will
rapidly lead to tangible atmospheric
concentration reductions. Gases with a longer
lifetime reach higher atmospheric concentrations
and experience a longer lag between emissions
reduction and atmospheric concentration
reductions. Reducing emissions of short-lifetime
potent gases such as methane is therefore a
valuable means of rapidly slowing global
temperature rise.
Figure 8: Effect of emissions cessation (a) and gradual reduction (b) on atmospheric concentration

24 Chapter 3: Methane emissions trading
One of the key issues in this report is whether
methane trading is a viable option for the UK.
Market based trading schemes are currently a
popular option for dealing with a range of
environmental issues. A consequence of the
diverse and diffuse nature of methane sources is
that policies with the potential to address the
mitigation of methane emissions are similarly
varied and tend to be focused within the
individual sectors (e.g. waste, agriculture, coal
mines). Methane emissions trading offers the
possibility of a consolidated approach that could
apply across all sectors.
This chapter explains the concept of emissions
trading and looks at both the UK and EU
Emissions Trading Schemes, before outlining the
options for trading methane. This sets the
contextfor the remaining chapters in which the
various sources of methane are discussed in detail
and the possibility of methane trading for each
sector is explored, amongst other policies for the
mitigation of methane emissions.
3.1 Emissions trading concept
Emissions trading is a mechanism for delivering
emissions reductions at minimum economic cost.
It is a move away from the traditional ‘command-
and-control’ regulatory approach to a market-
based mechanism, directly involving those
responsible for the emissions and allowing the
polluters to decide their own emissions
abatement pathway. Trading is therefore seen as
a highly attractive option by both corporations
and government and has become a central tenet
of international policy to reduce greenhouse gas
emissions, such as the Kyoto Protocol.
The UK has already implemented the first
industry-wide trading system incorporating
carbon dioxide, methane and other greenhouse
gases. The EU Emissions Trading Scheme starts in
2005, although initially this will only cover carbon
dioxide. Opportunities to include methane in the
EU ETS are under review, but it will be 2008 at the
earliest before methane is included.
Historically, trading was first proposed as an
environmental policy instrument in the 1960s.
35, 36
Trading has become an increasingly popular
measure over the last two decades, especially as
part of pollution reduction regimes in the USA. In
particular, trading is credited with the significant
reduction in emissions of sulphur dioxide (a major
source of acid rain), although it has been argued
that these reductions would have occurred
anyway.
37
As a policy tool, trading is well suited for GHG
emissions control because the costs of reducing
emissions vary widely between individual
greenhouse gases, sectors and countries,
providing opportunities and large potential gains
from trade.
38-40
The international carbon trading
market is expanding rapidly and more than
doubled in size in 2003 to 70 Mt CO
2
e.
41
How does trading work?
A traditional command-and-control approach
imposes absolute performance or technological
standards on companies, but takes no account of
the individual economic burden placed on those
companies.
42
Such an approach is illustrated in
Figure 9a, where the two plants face different
abatement costs for achieving the same
reductions in emissions. In Figure 9b, under
emissions trading, the market determines the
price of the commodity and the benefit to the
company is determined by the difference
between the abatement cost and market price.
For instance, plant 1 gains £15 since it can reduce
emissions by one tonne at a cost of £5 and then
sell this credit on the market for £20. Instead of
plant 2 actually undertaking emissions reductions
and paying £30 per tonne, it can purchase a credit
on the market for £20, thereby making a saving of
£10 compared to the regulated approach. Hence,
the overall cost of reducing two tonnes under
trading is just £10, instead of £35 under the
regulated scenario shown in Figure 9a.
Trading therefore has the advantage of
enabling the most cost-effective implementation
of the overall target, with cost benefits to all
Methane emissions trading

companies irrespective of their individual
abatement costs. Furthermore, trading provides
incentives to invest in environmentally sound
technologies. Emissions trading is thus seen as
the “least bad of all options”
43
in terms of policy.
The carbon trading market is merely a
mechanism for ensuring that baseline targets are
met and its success in achieving significant
greenhouse gas emissions reductions depends
simply on where the baseline is set. Emissions
trading combines buying and selling of emissions
with the right to emit GHGs, identified through
company or country specific allowances (also
referred to as quotas, permits or caps). The total
allowance of a regulated pollutant is determined
centrally by government or international bodies.
This baseline is reduced over time to achieve the
desired emissions reduction in the required
timeframe.
Allowances are distributed to entities, allowing
market forces to control their price, and can be
assigned in two ways: either through an auction,
where allowances are sold on a market basis, or
by ‘grandfathering’, where allowances are
allocated on a discretionary basis, typically based
on the historical emissions of an entity. Ideally,
the system should reward companies that have
already taken action to reduce emissions and
penalise those that have not; grandfathering
enables such flexibility. Within a classic ‘cap and
trade’ scheme, participants take on targets
requiring them to reduce their emissions to a
capped level, which may be more or less stringent
than the overall baseline reductions.
Trading emissions is no different from trading
other commodities. Once allocated or created,
emissions allowances act as fully interchangeable
commodities and they can be bought, sold and
traded, or in some circumstances banked for
future use. Account holders in a central registry
can buy and sell allowances and trade either
between themselves or with third party brokers.
Entities with low abatement costs (costs of
reducing emissions) or those that reduce their
emissions by more than their allocated amount
can sell their surplus (‘carbon credits’) to others
who are not able to reach their target easily.
42
Conversely, companies that exceed their limits
can choose to purchase allowances on the open
market to match their emissions or invest in
abatement technology, generally whichever is
cheaper. The market price of allowances will rise
if the overall baseline is not being achieved, since
demand will increase, and fall if overachieved.
Allowances can even be retired without
counterbalancing an actual emission thereby
making the adopted baseline stricter and creating
an additional environmental benefit.
25 Chapter 3: Methane emissions trading
Figure 9: Comparison of (a) regulated approach & (b) market trading approach

26 Chapter 3: Methane emissions trading
When trading methane that has been
combusted, either by flaring or to recover energy,
the negative impact of emitting the combustion
product carbon dioxide must also be accounted
for. Burning one tonne of methane (equivalent to
21 tonnes of carbon dioxide) produces 2.75 tonnes
of carbon dioxide. One tonne of combusted
methane is therefore equivalent to 18.25 tCO
2
e
(21 - 2.75).
3.2 Emissions trading schemes
International Emissions Trading is the major
mechanism of the Kyoto Protocol but, with the
delay in ratification, other emissions trading
schemes have been developed, most notably the
UK and EU Emissions Trading Schemes (UK ETS
and EU ETS).
UK Emissions Trading Scheme
The UK ETS was launched in April 2002 as a
voluntary scheme to run until December 2006.
The aims of the UK ETS are two-fold: to deliver
cost-effective greenhouse gas emissions
reductions and to provide UK industry with
practical experience of emissions trading ahead
of a European or international system. In this
manner, UK businesses should be well placed to
take a leading and influential role in both
development and use of these wider schemes.
The UK ETS was expected to deliver total savings
of 2-4 Mt CO
2
e by 2006 through encouraging fuel
switching in power generation, principally from
coal to gas.
Both direct and indirect emissions are covered
in the UK scheme, meaning that emissions
associated with both the generation and use of
energy are included. The scheme covers all
industrial sectors apart from power generators.
Landfill sites, households and the transport sector
are all exempt.
The UK ETS is also unique in that it is a multi-
gas trading system. Methane has been actively
traded as part of this scheme by participants such
as UK Coal, Shell and BP.
44
Allowances are traded
in the ‘currency’ of carbon dioxide equivalents; the
exchange rate for methane is simply the 100 year
GWP of 21.
Participation in the UK ETS takes three forms:
direct participation, as a climate change
agreement (CCA) participant and as a trading
participant. All participants are committed to the
scheme for its full duration.
Direct participants operate on a ‘cap and trade’
basis and are required to make an absolute
reduction in emissions against a 1998-2000
baseline over the period 2002-06. If targets are
not achieved, penalties, and ultimately fines, are
incurred. To encourage participation in the
scheme, participants received incentive payments
from the Government, set through a competitive
bidding process. The UK Government committed
a total of £215m incentive money (after tax),
payable over five years (2002-6).
45
A total of 34 companies were successful in the
auction of the five-year allowances, which took
place in February 2002. These include Ineos Fluor,
Dupont, Shell, UK Coal and BP. Collectively these
companies have committed to reduce emissions
by around 4 MtCO
2
e/yr by December 2006. At
the end of each year, organisations have a three
month reconciliation period to compile their
verified emissions report. By the end of this
period they are required to demonstrate to the
Government that they have sufficient allowances
to cover all of their emissions. The first year
results show 31 out of 32 direct participants met
their emissions reductions targets.
45
All
participants trading methane are acting as direct
participants.
Climate change agreement participants are
those companies already covered by the Climate
The UK ETS covers
emissions from both the
generation and use of
energy

27 Chapter 3: Methane emissions trading
Change Levy (CCL). These participants use the
emission or energy targets previously set through
the CCL agreement, which, if met, entitle them to
an 80% discount on the levy. This form of trading,
sometimes referred to as ‘baseline and credit’, is
used to either help meet the target by purchasing
allowances, or by selling any over-achievement. If
the target has been met and the over-
achievement verified, allowances are given at the
end of each compliance period. Targets for CCA
participants are defined in terms of absolute
emissions reductions (tonnes CO
2
e) or relative
targets according to levels of output (tonnes CO
2
e
per tonne product).
CCA participation covers 866 firms
46
which are
expected to deliver additional emission
reductions of over twice that of direct entry ETS
participants.
47
Trading participants are companies, brokers or
individuals not subject to reduction targets who
opened trading accounts with the Emissions
Trading Registry, which they then use to buy or
sell allowances. In the first year of trading there
were 35 active trading participants.
46
A fourth option that has been considered in
the UK, but is not part of the current scheme, is
participation through projects: the generation of
credits from new emission reduction projects in
the UK. Under this route, projects are not
assigned a baseline and therefore the emissions
reductions have to be quantified. The savings
must also be additional (i.e. the reductions would
not have occurred without the project). The UK
Government decided not to use this option
because of the risks associated with it in light of
the EU’s proposal for linking Joint Implementation
(JI) and Clean Development Mechanism (CDM)
projects into the EU ETS.
48
EU Emissions Trading Scheme
The EU ETS starts on 1 January 2005 and will be
the first multinational scheme in the world with
emissions trading between Member States of the
enlarged European Union.
The European scheme is mandatory and covers
only direct emissions. It is divided into two
phases: an initial phase (2005-2007) and a main
phase (2008-2012) concurrent with the first
commitment period under the Kyoto Protocol. Six
sectors are covered: energy activities (all plants
over 20 MW), oil refining, cement production, iron
and steel manufacture, glass and ceramics, and
paper and pulp production. The first phase of the
scheme will only cover carbon dioxide emissions,
but this will be reviewed by the Commission in
2006 and may be extended to other greenhouse
gases, including methane. Gases not covered
under the Kyoto Protocol may still be eligible for
trading. Additional sectors will also be
considered. The scheme may also be expanded to
permit European companies to carry out
emissions curbing projects around the world, as
proposed by the European Commission in the
‘Linking Directive’. This would convert credits
earned into emissions allowances in the same
manner that JI and CDM projects would work
under the Kyoto protocol.
Member states were required to develop a
national allocation plan for emission permits to
companies by March 2004. This grandfathering
process set targets for the relevant sectors and
delineated methods for division of allowances
(each worth 1 tonne CO
2
) between participants of
the respective Member States. The Directive
allows up to 5% of allowances to be auctioned in
2005 and 10% after 2008. So far this process has
resulted in a great deal of controversy with
companies disputing their allocations.
All installations must meet their targets by
reducing emissions or by buying allowances.
Installations without sufficient allowances to
cover their emissions will pay a direct financial
penalty (40 € per tonne CO
2
from 2005-7, 100 €
per tonne thereafter) and have to make up the
deficit in subsequent commitment periods. For
installations that have a surplus of allowances,
Member States can allow banking.
More than 12,000 installations – representing
approximately 46% of the EU’s total carbon
dioxide emissions – will participate in the scheme.

28 Chapter 3: Methane emissions trading
Market analysts predict that trading could be
worth more than €7-8 billion a year by 2007,
creating a brand new financial market.
49
Although the scheme does not start until 2005,
the first deals have been brokered already with up
to 250,000 credits traded in just one day.
50
Interaction of the UK and EU ETS
The UK and EU Emissions Trading Schemes differ
on a number of issues (Table 7), which essentially
make the two systems incompatible. One of the
key differences lies in the trading arrangements:
the EU scheme considers direct emissions only
Table 7: Comparison between the UK and EU Emissions Trading Schemes
UK ETS EU ETS
Type of
scheme • Voluntary • Mandatory
Period • 1st period 2002-2006 • Phase 1 2005-2007
• No guarantee of 2nd period, • Phase 2: 2008-2012
but review in 2005
GHGs • All six GHGs • Only CO
2
in Phase 1
• Other gases may be included in Phase 2,
provided adequate monitoring and reporting
systems are available and provided there is
no damage to environmental integrity or
distortion to competition
Sectors • Indirect and direct emissions • Direct emissions (source) only
(end-user) • Subset of IPPC sectors, excluding chemicals,
• All industrial sectors except food and drink and waste incineration
power generators • Energy activities (all plants over 20 MW), oil
•Transport, landfill, households refining, cement production, iron and steel
exempt manufacture, glass and ceramics, and paper
and pulp production
Type of • Direct entrants (absolute targets) • Absolute targets for all participants
targets • CCA participants (absolute or
relative targets)
Market size • 34 direct entrants (~ 1 MtC- • More than 12000 installations (Phase 1)
reductions over 5 years) • 46% of EU carbon dioxide emissions
• ~6000 CCA businesses (~ 2.5
MtC/year)
Allocation • Financial incentive (auction) for • Member states decide allocation method.
method direct entrants They have the option to auction up to 5% in
• Negotiated energy saving targets Phase 1 and 10% of allowances in Phase 2
through CCAs • Commission retains the right of veto over
national allocation plans
Compliance • Loss and repayment of financial • Penalty of 40 €/tonne.
incentive for direct participants • Increased to 100 €/tonne after 2008
• Statutory penalties to be introduced
•CCA participants have separate
compliance procedures

29 Chapter 3: Methane emissions trading
whereas the UK ETS incorporates emissions from
end-users as well. Now that the EU scheme has
been approved to start in 2005, it is highly
unlikely that the UK ETS will continue beyond its
current phase (2002-2006). The UK Government
has confirmed that there will be no transfer of
credits between the two schemes.
Cessation of the UK ETS in 2006 will have
consequences on the trading of methane since
methane will not be included in the EU ETS until
2008 at the earliest.
Methane trading
Although methane is already being traded
successfully in the UK ETS, this is currently limited
to emissions from active coal mines and offshore
gas, thereby excluding a large proportion of other
anthropogenic methane emissions. With the
likely closure of the UK ETS in 2006, even this
restricted level of trading will cease. There is no
guarantee that methane will be incorporated into
the EU ETS in 2008 and even if it is, there will still
be a two year gap until methane trading is
possible again. This delay will act as a deterrent to
investment in methane capturing technologies if
trading is the main incentive.
A separate methane market is not a viable
option in the UK because the market would be
too small to be liquid. For methane to be traded
it must be incorporated into a multi-gas trading
scheme.
If methane is included in the EU ETS from
2008, there are two possible routes through
which methane could be introduced: through new
installations or via the project entry route.
New installations. As part of the EU ETS review
in 2006, new sectors beyond those specified in
the first phase will be considered for inclusion in
the scheme. This could open up methane trading
from sectors such as the gas industry.
Project entry route. New projects have the
potential to encourage emissions reductions, but
only if the emissions reduction obtained is
additional (i.e. they would not have occurred in
the absence of the project).
51
Through the
‘Linking Directive’, JI and CDM projects would
permit entities in industrialised countries to
develop greenhouse gas reducing projects.
However, because the EU ETS is focused on
large emitters of carbon dioxide, small-scale
emitters in the methane sector, such as farmers,
are unlikely to be able to participate without
aggregation.
3.3 Review of the UK ETS
The UK ETS has provided companies with
experience of trading and established a trading
support industry. However, there are some
aspects of the scheme that were not wholly
successful, providing valuable lessons in
developing an effective emissions trading
scheme.
In the first year of the UK ETS, trading went
well with over 32 million allowances allocated to
companies. Selling activity was initially
dominated by a few direct participants.
47
This
forced the price of carbon up to a peak of
£12.40/t CO
2
e in October 2002 (Figure 10). As
more CCA companies had their emissions verified
towards the end of the year, they then had
Methane will not be
included in the EU ETS
until 2008 at the earliest
Figure 10: UK ETS carbon prices, 2002-4
Source: DEFRA, 2004
55

30 Chapter 3: Methane emissions trading
emissions to offer to the market causing the
balance of selling activity to shift and the price to
slump to £5/t CO
2
e.
52
Such problems are partly
due to lack of liquidity in the UK market: the
market is highly skewed as a result of the
structure of the scheme, with very few players
and the sellers generally outweighing the
buyers.
53, 54
Also, activity is dictated by CCA
participants, who have provided much of the
buying activity so far,
54
as most trading occurs
when they need to demonstrate compliance once
every two years. Shorter compliance periods
would have ensured a more constant level of
trading. Shorter compliance periods would have
ensured a more consistent level of trading.
However, the direct participants are larger
companies with lower abatement costs, and have
sold to the CCA participants, who in general will
have higher abatement costs due to economies of
scale. In this sense, the scheme has been
successful in achieving emissions reductions at
lowest cost.
55
To date, approximately 2,000,000 allowances
(1 allowance equals 1 tonne CO
2
e) have been
traded in the market, of which 580,000
allowances were bought for CCA compliance.
Some sophisticated direct participants (e.g. oil
companies) have been active in both in buying
and selling, trading speculatively rather than as
direct participants. Activity in the UK ETS has
now dropped since CCA companies do not have to
prove compliance until February 2005 and so
there is no immediate incentive to purchase
allowances in the market. There is still a limited
amount of trading, with CCA companies buying at
the current low price to hedge against future risks
of price increases and meeting CCA targets.
Allowances purchased now can be banked and
used towards later targets.
The market integrity and environmental
effectiveness of the scheme was badly damaged
due to an imbalance in allocation of allowances
amongst the direct participants.
56, 57
Although
the achieved emissions reduction was over six
times greater than the direct participants’
collective target, the majority of savings came
from just two companies, both of whose
emissions were expected to fall anyway through
regulatory requirements.
56
In other words, DEFRA
awarded a huge ‘hot air’ surplus and
compromised the integrity of the scheme, a fact
which they have acknowledged.
55
The price of
carbon had slid down to £1.75/t CO
2
e by August
2003 as a result of oversupply from the direct
participants.
58
Hence, although the UK ETS might have
stimulated significant market activity, its
effectiveness in contributing to greenhouse gas
emissions reduction targets is questionable.
47
There is debate as to whether the scheme has
delivered significant quantities of absolute
emission reductions with participating firms
reducing emissions further than would have
occurred in the absence of the scheme.
3.4 Conclusions
Reflecting on the experience of the UK ETS, it is
possible to identify some critical factors essential
for effective emissions trading markets:
• Commodity to trade. To state the obvious, for
trading to occur, there has to be a product or
commodity to trade. This must be of sufficient
volume and from enough individual sources to
encourage liquidity. In practical terms, it must
be possible to quantify the amount of gas
recovered, which can be done most easily
through capture.
• A liquid market. Emissions trading schemes
must have sufficient supply and demand,
supported by financial derivatives, if they are to
function effectively.
59
In traditional commodity
trading, markets are driven by supply and
demand and the incentive to make profits, but,
in the case of emissions trading, the system is
driven by legislation which operates in a highly
uncertain environment. Trading markets work
more efficiently as their size increases. The
more liquid the market, the more quickly a
market price is established, offering greater
certainty to all market participants.

31 Chapter 3: Methane emissions trading
• Suitable mix of players. Markets do not
function efficiently if there is disparity in the
size of players. Under the UK ETS, two large
companies dominated the selling activity, set
against the thousands of small CCA
participants as buyers. For brokers, it is more
cost efficient to trade large volumes of
commodities than small volumes with many
players, as the transaction cost for the latter
will be high.
54
• Additionality. It is a primary requirement of any
trading scheme that credits for reducing
emissions must be additional to those required
to fulfil other regulatory obligations such as the
Renewables Obligation. This will avoid the
double counting of emissions reductions (‘hot
air’) that occurred in the UK ETS.
56
This also
means that any new legislation will affect the
viability of trading and, conversely, participation
in a trading scheme makes legislating difficult.
Governments are therefore faced with a choice
as to whether to legislate or allow trading. This
is a particularly difficult decision with regards
to methane in the UK due to the two year gap
between the UK ETS finishing and methane
being introduced into the EU scheme.
• Monitoring, reporting and verification.
Standards must be in place for setting baselines
and reporting and verifying emissions for an
entity. High standards of monitoring, reporting,
verification and compliance are crucial to
guarantee the environmental integrity and
financial credibility of any emissions trading
scheme.
60, 61
A reliable baseline against which
savings can be measured is crucial. This gives
certainty to what is being exchanged, the
obligations to be met and sanctions to be
imposed (in the case of non-compliance).
Accurate verification of emissions also helps
prevent incorporation of ‘hot air’ into the
trading system, which can lead to a fall in
market price.
• Conflicting policies. It is important to identify
whether there are existing policies which may
conflict with the trading scheme and thereby
affect viability of the market. For instance, if
the price of ROCs is higher than the market
price for carbon, companies may choose not to
trade and opt for ROCs instead.
Potential for methane trading
Methane trading has the potential to act as a
strong incentive towards achieving significant
reductions in methane emissions. However, not
all methane produced in the UK will be eligible
for trading: the diversity of methane sources
means there is similar diversity in the feasibility
of trading amongst different methane generating
sectors. The criteria identified here will be used in
the following chapters to assess the potential for
methane trading in each of these sectors.

32 Chapter 4: Methane in the UK
The UK is party to the UN Framework Convention
on Climate Change (UNFCCC), which came into
force in 1994 and requires accurate reporting of
emissions. The UK is committed to reducing
greenhouse gas emissions to 12.5% below 1990
levels by 2010. As a UNFCCC signatory, the UK
must monitor progress towards achieving these
targets by compiling a UK inventory and
publishing an annual inventory report which
includes a break down of emissions by
anthropogenic source. The National Atmospheric
Emissions Inventory
62
provides detailed methane
emissions data from 1990, enabling major trends
and the relative contribution of different sources
to be identified.
Reports have been published annually since
1995, although it is important to note that figures
in these reports have been revised over time as
monitoring and modelling procedures have been
refined and become more accurate. Emissions
data for 1990 have therefore altered over the
course of the inventory development and baseline
levels for Kyoto Protocol commitments have also
changed.
4.1UK methane sources
In 2002, 2.10 Mt of methane was emitted from
anthropogenic sources in the UK.
63
This
represents 6.9% of all UK GHG emissions. On a
global scale, the UK is responsible for
approximately 0.7% of all anthropogenic
emissions of methane, from approximately 1% of
the world’s population.
The major sources of methane in the UK are
agriculture, landfill waste, natural gas leakage
and coal mining. Together these sources account
for 95% of total anthropogenic emissions
(Figure 11).
Agriculture is the dominant anthropogenic
source of methane, responsible for 0.91 Mt(CH
4
)
of emissions in 2002. Of the total agricultural
emissions, around 90% is derived from the
digestive processes (enteric fermentation) in
animals, whilst the remainder is from animal
wastes. The second largest anthropogenic source
of methane in the UK is the anaerobic
decomposition of biodegradable waste in landfill,
accounting for 0.46 Mt(CH
4
) of emissions.
Leakage from natural gas distribution and
emissions from active coal mines account for a
further 0.39 and 0.24 Mt(CH
4
) respectively.
However, it is important to note that the
methane seepage is from active coal mines only;
emissions from old unused mines are not
included in the inventory. Inclusion of abandoned
coal mines would add up to a further 0.3 Mt to
UK methane emissions.
64
Other measurable
sources of methane include manufacturing,
transport and waste water handling, accounting
for 0.10 Mt(CH
4
) per year.
4.2Historical trends
Historically, coal mines were the dominant source
of methane in the UK. However, after the miners’
strike in 1984, the coal mining industry declined
and emissions from active mines fell as the
number of working pits decreased (Figure 12). By
1990 landfill sites had become the primary source
Methane in the UK
Figure 11: UK sources of methane, 2002
Source: Baggott, 2004
63

of methane. However, emissions from landfill
sites have decreased throughout the 1990s,
mainly due to improvements in methane
capturing technologies and improved landfill caps
(Chapter 5). Since 1993, the agricultural sector has
been the dominant source of methane in the UK.
Emissions reductions within this sector have been
small, so the relative importance of agriculture to
total UK methane emissions has steadily
increased.
Since 1990, the baseline year for the Kyoto
Protocol, there has been a reduction in methane
emissions from all methane-emitting sectors.
Most notable is the drop in emissions from coal
mines, which decreased by approximately 70%
between 1990 and 2002 (Table 8). This is due to
the decline in the number of operating mines in
the UK. Emission reductions from active coal
mines are deemed responsible for 37% of the total
methane reductions and 12% of all greenhouse
gas emissions reductions since 1990, according to
the UK inventory. However, because emissions
from abandoned mines are not included in the
inventory, this is unlikely to be a true
representation of ‘real’ methane emissions from
this source.
Significant reductions in methane emissions
arising from landfill sites have also been achieved
over the last decade. Between 1990 and 2002,
emissions fell by 61%, accounting for 45% of the
overall reduction in methane over this period.
Since 1990, methane emissions in the oil and gas
industry have declined by 24%. The smallest
methane reduction was within the agricultural
sector, where emissions fell by only 13% despite
the well-publicised livestock farming crises of BSE
and Foot and Mouth, which affected livestock
numbers.
The significant reductions made by some
sectors but not others pose questions to
technologists and policy makers alike. Have
landfill gas abatement technologies reached their
potential, making further reductions expensive?
Are the small reductions observed from the
agricultural sector because it is inherently difficult
to reduce emissions without reducing animal
numbers and damaging the industry? And what
policies should be implemented to maximise
further emissions reductions at minimal economic
and social cost? These issues are discussed on a
sector-by-sector basis in Chapters 5 to 8.
4.3Breakdown by region
In 1999, legislation was introduced to devolve
power to the regions of the UK and led to the
formation of the Scottish Parliament, National
Assembly of Wales and the Northern Ireland
Assembly. It is the responsibility of these
devolved administrations to ensure that Kyoto
targets are met in their areas. The UK
Government is responsible for ensuring such
targets are met in England and also retains some
over-arching powers such as taxation measures
that can be applied to the entire UK.
It is therefore useful to examine the regional
spread of greenhouse gas production in the UK to
provide data relevant to England and each of the
devolved administrations. Disaggregated data
33 Chapter 4: Methane in the UK
Figure 12: Long term
trends in methane
emissions, UK
Source: DEFRA, 2003
65
Table 8: UK methane emissions from 1990-2002 (Mt CH
4
)
% decrease
1990 1995 2000 2002 1990-2002
Landfill 1.17 0.97 0.59 0.46 61%
Agriculture 1.03 1.01 0.97 0.91 13%
Natural gas 0.51 0.48 0.40 0.39 24%
Coal mines 0.82 0.50 0.27 0.25 70%
Other 0.13 0.10 0.10 0.10 22%
Total emissions 3.66 3.06 2.32 2.11 43%
Source: Baggott, 2004
63

34 Chapter 4: Methane in the UK
exist for the four home nations for 1990, 1995 and
1998 to 2000
66
(Table 9).
Table 9: Regional breakdown of methane and
total GHG generation, UK, 2000
All greenhouse
Methane (%) gases (%)
England 71.5 73.6
Scotland 11.6 10.9
Wales 8.6 8.0
Northern Ireland 5.9 3.2
Unallocated 2.4 4.2
Source: Salway, 2003
66
The regional production of methane follows the
same trends as total GHG emissions, as might be
expected from simple farm area and population
arguments. A regional breakdown by source
presents a different picture, with agriculture
being more predominant, and landfill less
important, in the more sparsely populated
nations with their mainly rural economy. Oil and
gas emissions are concentrated in the more
industrial nations, and coal emissions only from
those nations with active coal mines (Figure 13).
4.4Data uncertainties
Whilst the general trends in methane emissions
data are widely accepted, there is less confidence
surrounding the exact figures presented. The IPCC
reports this to be a generic problem, hindering
efforts to provide quantitative projections of
future methane emissions.
1
Since the UK’s first submission to the UNFCCC
in 1997, the emissions inventory has undergone
substantial revision (including the 1990 baseline
figure). A number of studies were commissioned
with the aim of quantifying methane emissions
more accurately. In particular, estimates for
landfill emissions have been reduced significantly
and figures for gas pipeline leakage have been
increased. Despite these efforts, the uncertainty
level for methane emissions data is ±14%
overall,
63
and higher for individual sources.
Variations in emissions estimates from landfill are
±48% and for gas pipe leakage between 17 and
75%, depending on the type of gas main and
service. In the agricultural sector, animal
numbers are accurately known (±1%), but the
emission per animal error is estimated at ±20%.
Similarly, the emission factor for coal mines is
predicted with an uncertainty of ±13%.
Further revisions can be expected in the future,
as methodologies for quantifying methane
emissions are refined and uncertainty levels
reduced. In addition, there are several
outstanding issues to be addressed, such as the
inclusion of abandoned coal mines, which may
substantially affect emission totals.
The high levels of data uncertainty are a cause
for concern, as it is becomes difficult to quantify
emissions reductions. Furthermore,
contradictions between the models on which
UNFCCC submissions are based and real-world
experience are possible. This is particularly
important for methane trading, where baselines
are set to produce overall GHG emissions
reduction targets. Should a project be able to
capture more methane than its targets because
the targets set are found to be based on
Figure 13: Methane emissions by source and region, 2000
Source: Salway, 2003
66

35 Chapter 4: Methane in the UK
inaccurate or uncertain data? If so, then that
project will be financially rewarded for what is
effectively ‘hot air’. The presence of ‘hot air’ in
trading systems can cause a collapse of the
trading price and ruin the effectiveness of such a
scheme for all participants, as discussed in
Chapter 3. It is clear that if significant and
sustained reductions in GHGs are to be achieved
through trading then the accuracy of emissions
quantification will need to improve across all
sectors. This should be made a major focus of
greenhouse gas abatement policy.
4.5UK greenhouse gas emissions
Carbon dioxide makes up the majority of GHG
emissions, although production has declined over
the past 12 years by 8% largely due to the ‘dash
for gas’: switching to cleaner natural gas
combustion (for electricity generation) from the
more polluting oil and coal. This has resulted in a
cleaner energy supply, but there are signs that
carbon dioxide emissions are now rising again
due to increased energy consumption. In
contrast, methane and nitrous oxide emissions
have both declined by approximately 40% in the
same period. This has resulted in an overall
decrease in emissions from the basket of six
greenhouse gases of 15% (Table 10).
Since the Kyoto base year of 1990, UK methane
emissions have fallen by 1.57 Mt from 3.67 Mt to
2.09 Mt, equivalent to 33.0 Mt CO
2
e. This is a drop
of 43%, accounting for 30% of GHG emissions
reductions since 1990, which dwarfs the 8%
emission reductions of carbon dioxide over the
same time period. Other greenhouse gases (N
2
O,
HFCs and PFCs) have achieved similarly high
emissions reductions.
The reduction in methane emissions has been
a major contributor to meeting targets as laid out
by the Kyoto Protocol. However, because almost
half of the reduction in methane emissions is due
to the closure of coal mines and non-inclusion of
emissions from abandoned mines, the ‘real’
reductions achieved may not be as significant as
the UNFCCC submissions portray. This picture will
change substantially once a methodology for the
inclusion of emissions from abandoned coal
mines is agreed and included.
So far, the UK is one of the few Annex I nations
to have reduced greenhouse gas emissions over
Table 10: UK GHG emissions 1990-2002 (Mt CO
2
e)
CO
2
CH
4
N
2
OHFCs PFCs SF
6
Total % CH
4
1990 584.0 76.9 67.9 11.4 1.4 1.1 742.6 10%
1995 547.6 64.3 57.0 15.5 0.5 1.3 686.1 9%
2000 542.6 48.8 44.8 9.1 0.5 1.9 647.7 8%
2002 537.4 44.1 41.0 10.4 0.4 1.6 634.9 7%
Decrease 1990-2002 8% 43% 40% 33% 16% –23% 15% 30%
Note: 1 Mt CO
2
e = 21 Mt CH
4
Source: Baggott, 2004
63
Coal accounts for more
than a third of UK
electricity generation

36 Chapter 4: Methane in the UK
the 1990 baseline (Figure 14). A 13% reduction in
2000
67
slipped to a 12% reduction in 2001.
68
Emissions in 2002 did, however, show a maximum
observed reduction of 15%,
63
but are predicted to
rise again in 2003 because of an increase in coal
burning in power stations as opposed to gas, due
to relative market prices. This has provoked
considerable debate as to whether or not
emissions reductions will be maintained in the
long term and, in particular, whether the UK will
meet its Kyoto commitment.
The basis for this scepticism lies in the manner
in which emission reductions have been achieved
to date. In particular, the majority of emission
reductions witnessed over the last decade are not
the result of targeted policy. Rather, carbon
dioxide emissions were inadvertently cut by an
economically-driven shift in the energy resource
base, away from a coal intensive industry towards
gas-fired and nuclear power. However, such good
fortune is unlikely to continue indefinitely: the
planned decommissioning of nuclear power
stations, along with forecast economic growth
and increases in road traffic, are expected to
increase carbon dioxide emissions over the
forthcoming decades. The UK Government
maintain that the Kyoto target will be met, with
baseline projections showing emissions to be
around 15% below 1990 levels in 2010.
69
Further
policy measures were introduced in the Third
National Communication
11
which, if successfully
implemented could increase the reduction to 23%
by 2010.
However, there is mounting evidence that the
UK’s efforts to meet the greenhouse gas target
are “slipping off track”. In any case, DEFRA confess
to having long-term concerns regarding UK’s
greenhouse gas emission trajectory. Baseline
projections point to a rise in emissions in the
post-2010 period, which by 2020 could leave the
UK in breach of current and future rounds of
Kyoto commitments.
69
With the stringent targets
set in the 2003 Energy White Paper, the UK has
reinforced its commitment to tackling climate
change.
The recent increases in GHG emissions due to
carbon dioxide need to be addressed by increased
energy efficiency, an increase in renewable
electricity and reducing consumption from the
transport sector. However, due to its high GWP,
further reductions in methane emissions still
have a significant role to play in meeting short
term targets, such as those agreed under the
Kyoto Protocol, and may buy time for carbon
dioxide abatement and renewable energy
technologies to be developed.
Figure 14: UK greenhouse
gas emissions, 1990-2002
Source: Baggott, 2004
63

37 Chapter 5: Waste and landfill
Waste in the UK is big business: the UK services
market for waste management is valued at about
£5bn, with the potential to grow to at least £12bn
over the next 10 years.
70
This market, which
comprises approximately 0.5% of the UK GDP,
involves an estimated 3500 firms.
71
Each year,
over 400 Mt of waste is produced in the UK
alone,
65, 70, 72
most of which ends up in landfill
sites. By far the majority of this waste (~370 Mt)
arises from agriculture, the mining and quarrying
industry, and the construction and demolition
industry
73, 74
(Figure 15). Landfill sites account for
22% of UK methane emissions (0.46 Mt).
In terms of methane production, the critical
factor is the amount of biodegradable waste sent
to landfill sites. Municipal waste (from
households and small businesses), although only
a small proportion of total waste production,
comprises the most biodegradable matter and
therefore generates the most methane. Both
agricultural waste (Chapter 6) and sewage sludge
can be highly biodegradable. Sewage sludge is
not considered here since it represents less than
1% of total waste generated. The other waste
streams contain only a minute fraction of
biodegradable material. Therefore the main focus
of this chapter is municipal waste.
The generation of methane from
biodegradable waste in landfill is the most
complex of all the sectors explored in this report.
The quantities of methane arising depend on the
qualities and quantities of waste and the waste
disposal methods chosen. The proportion of
methane captured, rather than emitted to the
atmosphere, is dependent on the landfill cap
technology employed. Furthermore, any methane
captured may be burned to generate heat or
electricity. In the latter case, the methane counts
as a renewable energy resource and is eligible for
valuable Renewable Obligation Certificates. The
challenge is to find the optimum balance
between environmentally benign waste disposal
practices, renewable energy generation and
minimising GHG emissions to the atmosphere.
This poses a host of challenges at the waste-
energy-climate change interface.
5.1 Methane from landfill
The production of methane in landfill is a result
of the restricted availability of oxygen during the
decomposition of organic waste. Many modern
landfill management practices aimed at
improving safety and environmental control have
paradoxically accentuated the generation of
methane by restricting airflow to the site.
Improving aeration can reduce methane
production, as has been successfully practised in
Japan, although this process is energy intensive.
Also, the introduction of air into landfill creates an
explosion hazard, if oxygen concentrations are too
high, and a greater risk of fire due to the higher
temperatures reached by aerobic decomposition
processes.
75
The amount of methane emitted to the
atmosphere depends almost entirely on the
design and management of the landfill and the
quantity of biodegradable waste entering the
landfill. Unchecked, the landfill gas will migrate
through the site in response to gradients of
pressure or gas concentration, or simply along
paths of least resistance. The gas may migrate
through the waste (depending on its
permeability) or through cracks and fissures in
Waste and landfill
Figure 15: Estimated annual waste by sector (by mass)
Source: DEFRA, 2003
65

38 Chapter 5: Waste and landfill
the compacted waste or bedrock material. In the
absence of obstacles, such as impermeable liners
along the landfill perimeter, the gas can travel
considerable distances from the boundary of a
site, for example, along buried utility installation
routeways (i.e. pipes for water, gas or sewage, or
channels for electricity and telecommunications
cables). Similarly, the propensity for migration to
the atmosphere depends largely on the
permeability of the landfill cover. Sand and gravel
caps will do little to impede vertical migration of
the gas, whilst more impermeable silts and clays
can successfully restrict this movement. However,
any weaknesses within the capping layer will be
readily exploited.
In a modern, well-engineered landfill,
deposited waste is mechanically compacted to
eliminate voids and then sealed with a low-
permeability capping layer, usually clay. This
process restricts the availability of oxygen within
the site, so that, once capped, the majority of
waste decomposition is carried out anaerobically.
The resultant landfill gas typically consists of
between 40 to 60% methane (by volume) with
the remainder being mainly carbon dioxide and a
host of trace constituents. The actual
composition of landfill gas is dependent upon a
number of factors, most importantly the
degradable organic carbon content of the waste
and the speed at which the material degrades.
The composition also changes over time as
biochemical conditions alter during the process of
decay.
Laboratory studies have identified five main
stages in the process of waste decomposition and
the process is relatively well understood
76
(Table
11). Methane production is variable over these five
phases and, even within the methanogenic phase,
production of methane depends upon the mix of
easily digestible biodegradable material versus
harder to digest materials such as wood. Some
carbon based materials will not decompose and
will remain in the landfill. It has been estimated
that 6.6 Mt of the 18.6 Mt of carbon going to
landfill remains and is sequestered there.
32
Because the emissions of methane are so
Table 11: Methane formation in landfill
Phases Description Time Gases
Phase 1 Aerobic phase where easily degradable organic matter is decomposed in the Days to a CO
2
increases
Initial adjustment presence of oxygen (from air trapped in landfill), resulting in CO
2
generation. month O
2
& N
2
decrease
Phase 2 Oxygen is depleted and anaerobic conditions begin to develop. CO
2
is 2 weeks or N
2
& O
2
decrease
Transition phase produced as complex organic compounds undergo hydrolysis and acid more CO
2
,H
2
& H
2
S
fermentation. increase
Phase 3 Hydrolysis converts organic matter to intermediate compounds, including 3 months CH
4
produced.
Acid phase acetic acid and volatile fatty acids. Acids accumulate in leachate. or more H
2
& CO
2
reach
Methanogenesis begins. maximum
concentration
Phase 4 Hydrolysis continues and methanogens proliferate. Methanogens convert May be as CH
4
production
Methanogenesis acids, H2 and CO2 into methane. For slowly biodegradable organic compounds long as 30 increases
(e.g. cellulose from paper and wood) this process continues for many years. years H
2
& CO
2
decrease
Phase 5 Readily available biodegradable material has been converted to methane and Decades CH
4
& CO
2
Maturation phase carbon dioxide, and emissions decrease. Air diffuses back into landfill. decrease
N
2
& O
2
increase
Source: Ong, 2003
76

39 Chapter 5: Waste and landfill
variable over time, it is exceptionally difficult to
predict how much methane is produced by
landfill. Whilst it is easy to measure the quantity
of gas captured, estimating the amount of
methane lost to the atmosphere through the cap
is much more difficult, as it is impossible to
predict accurately how much methane is
generated. Furthermore, the quantity of methane
escaping to the atmosphere is not simply the
difference between production and capture; some
methane may be oxidised in the capping layer
through contact with low-affinity
methanotrophic bacteria, particularly close to the
surface of the site. Such contact can reduce
methane content through oxidation to form
carbon dioxide, although the importance of this
in reducing overall emissions is unclear.
77
5.2 Landfill in the UK
The current dominance of landfill in the UK is a
result of economics, geography and advances in
construction and maintenance. Due to the
hydrology and geology of England and Wales, this
option is more economically favoured as a waste
disposal option compared to elsewhere in
Northern Europe.
78-80
Over the last six years, the amount of waste
sent to landfill has stayed roughly constant,
whilst recycling or composting has more than
doubled (Figure 16). Around 75% (34 Mt) of
municipal waste is sent to landfill each year by
the devolved administrations, with the remainder
incinerated, recycled or composted. This is
estimated to contain more than 21 Mt of
biodegradable matter, based on the assumption
that between 60 to 70% of municipal waste is
biodegradable.
81-85
There is uncertainty around the exact number
of landfill sites in the UK, estimated to be around
1500
156
. In England and Wales there were 2,300
working landfill sites in 2003, a fall from about
3,400 in 1994, although newer sites are larger. It
is estimated that the total area of land taken for
landfill sites is about 28,000 hectares – almost
0.2% of the land area of England and Wales.
Landfill policy
The primary focus of waste policy in both the UK
and EU has been on waste reduction rather than
specifically targeted at methane. The main policy
in the UK to date with regards to landfill has been
the Landfill Tax, which centred on diverting waste
away from landfill. Whilst such policy has
influenced methane emissions to a certain extent,
a more coherent and focused approach
addressing methane emissions abatement
directly is likely to be more effective in this area.
The EU Landfill Directive represents a move in this
direction, supported by the IPPC Directive (see
below).
The waste management hierarchy (Table 12) is
a central feature of European waste policy and, as
such, has been adopted by the UK. This approach
prioritises elimination and prevention of waste
over minimisation, re-use, recycling, recovery,
treatment and disposal. Moving up the hierarchy
leads to more sustainable methods of waste
management and increases the possibilities for
reducing methane production. The hierarchy has,
however, been criticised for not necessarily
Figure 16: Disposal methods of municipal waste, England, 1996-2003
Source: DEFRA, 2004
86
Year

40 Chapter 5: Waste and landfill
reflecting what is best for the environment.
87
Certainly the relative merits of landfill and
incineration, with and without energy recovery,
are unclear.
Current waste management practices within
the UK, with heavy reliance on landfill, are
weighted towards the bottom of the hierarchy;
generally the least environmentally friendly but
most cost-effective and easiest waste
management options for the local authority.
It is difficult to deliver waste strategies that
focus on the top levels of the waste hierarchy.
Successful implementation of such policies
requires large-scale social change; many
thousands of people each altering their personal
waste disposal habits to a more environmentally
benign method. Whilst some will be enthusiastic
about such issues, achieving a widespread
conversion is an uphill battle requiring resources
and education.
UK Landfill Tax
The Landfill Tax was introduced in the UK in
October 1996 and is levied on disposal of waste to
landfill, with very limited exemptions, operating
on the ‘polluter pays’ principle.
88
It intends to
promote diversion of waste from landfill through
increasing the economic viability of sustainable
waste practices, such as re-use, recycling and
composting, by imposing a tax on landfill waste.
Landfill operators are liable for the tax on all
consignments of waste accepted for landfill
disposal. In practice, the costs are passed through
the waste management chain and the landfill
operator pays the levy to Customs & Excise.
Introductory tax rates were set in 1996 at £7 per
tonne of active waste (mainly biodegradable
waste), and £2 per tonne of inactive waste. The
Landfill Tax ‘escalator’ was announced in the 1999
Budget. This raised the standard rate to £10 per
tonne and included a commitment to increase it
by £1 per tonne each year to £15 per tonne by
2004-05
79
and by at least £3 per tonne each year
thereafter, towards a rate of £35 per tonne in the
medium to long-term.
89
Has the Landfill Tax been effective?
To date, there is still confusion over the effect of
the Landfill Tax: the reduction in waste going to
landfill has not been documented and there is no
quantification of the amount of waste diverted.
What is available is a measure of the amount of
tax raised and fiscal contributions through the
Landfill Tax credit scheme, which offsets waste
going to landfill via investment in sustainable
waste projects. In 2001/2, over £500M of Landfill
Tax was generated, net of the contribution to the
credit scheme,
90
representing almost a five-fold
increase since introduction. However, despite the
tax, there has been a rise in the amount of waste
sent to landfill over the same period: in England,
municipal waste increased from 20.6 million
tonnes in 1996/97 to 22.1 million tonnes in
2000/01.
91
This puts into question the real
effectiveness of the Landfill Tax as a policy
instrument.
In 2000, the DETR
97
claimed the tax was
already having a “notable impact” on waste
management practices and a consultation
paper
98
stated that the tax “is already
encouraging some waste minimisation, re-use
and recycling”. On the contrary, a review of the UK
Landfill Tax in 2002, commissioned by DEFRA,
Table 12: The waste hierarchy and options for dealing with biodegradable matter
Level What this means for biodegradable waste Responsibility
Reduce Home composting
Less packaging Individuals
Lower consumption
Re-use Reusable packaging
Recycle Recycle paper and cardboard wastes
Recovery Obtain maximum energy from waste
Combustion of methane from anaerobic
digesters Local government
Incineration with energy recovery
Combustion of methane from landfill
Treatment Incineration without energy recovery
Disposal Landfill

41 Chapter 5: Waste and landfill
suggests that the tax plays a limited role in
encouraging people to recycle and compost and is
“largely irrelevant” in helping the UK achieve the
targets set out by the Landfill Directive.
92
The
ineffectiveness of the tax to stimulate changes in
behaviour has been attributed to its low level.
93-96
The EU Landfill Directive
The EU Landfill Directive 1999/31/EC, which was
adopted into UK domestic legislation in 2002, is
the most explicit policy addressing the reduction
of methane generated by landfill. It takes a dual
approach, aiming to decrease reliance on landfill
as a method of biodegradable waste disposal
coupled with requirements to install best-practice
methane recovery technologies. The Directive
makes it clear that landfill is the least preferred
method of waste disposal, with an emphasis on
moving up the waste management hierarchy
towards reuse, recovery and recycling.
Compulsory installation of gas collection and
disposal systems is stipulated, with emphasis on
energy recovery at new landfill sites. The
Directive also prohibits disposal of liquid wastes,
tyres and clinical wastes to landfill and
distinguishes between hazardous and non-
hazardous landfill.
The long-term objective of the Landfill
Directive is to reduce methane emissions at
source by diverting biodegradable waste away
from landfill. The Directive provides a series of
targets that require reductions in the amount of
biodegradable municipal waste sent to landfill.
These targets have been agreed by the UK
Government and Welsh National Assembly,
although, since the UK is heavily reliant on landfill
to dispose of its waste, it has been given an extra
four years by the EU to meet the requirements of
the Directive.
82
This means that the UK is
required to reduce the amount of biodegradable
waste to landfill to:
99
• 75% of that produced in 1995 by 2010;
•50%, by 2013;
• 35%, by 2020.
For the UK, this equates to a maximum of 13.1, 8.7
and 6.1 million tonnes of municipal biodegradable
waste to landfill in 2010, 2013 and 2020
respectively.
82
These dates include the four year
extension, which the UK is to adopt for the first
two target years with the decision still to be
made on the final target year.
100
IPPC Directive
The European Integrated Pollution Prevention and
Control (IPPC) Directive 96/61/EC provides further
support for the reduction of methane emissions
from landfill. The IPPC Directive was
implemented in England, Wales and Scotland
through the Pollution Prevention and Control Act
(PPC) in 2000. Industrial activities subject to
control under the PPC regime include certain
waste management operations. The PPC
demands that operators show they have
systematically developed plans to apply the best
available technology to prevent pollution or,
where that is not practical, to reduce it to an
acceptable level.
5.3 Methane capture
Under the EU Landfill Directive, from 2002, all
new landfill sites are required to capture the
methane produced, with energy recovery being
Municipal waste has
increased in quantity by
approximately 3% per
annum since 1996/7 –
faster than the
corresponding increase in
GDP

42 Chapter 5: Waste and landfill
the preferred option. A recent study has found
that the largest factor in the mitigation of
methane from landfill is through methane
capture, rather than diversion or recycling, due to
the quantities of waste already in landfill sites.
154
Historically, control of methane at landfill sites
was driven by safety concerns, rather than active
GHG emission control, due to the flammable
nature of the gas. The most basic systems merely
attempt to control the movement of the gas, with
the aim of avoiding lateral migration, thereby
avoiding the risk of fire and explosion at nearby
facilities. Such systems comprise impermeable
liners and a capping layer (usually clay), often
coupled with trenches or wells, which provide
convenient ‘vents’ through which gas can escape
to the atmosphere.
Technologies have become increasingly
sophisticated over the past two decades. In
particular, the integrity of impermeable liners and
capping layers has been vastly improved and
these are now considered a fundamental
component of landfill design. Improved landfill
caps on new sites are the main driver behind the
61% reduction in methane emissions from landfill
between 1990 and 2002 (Table 8). Additionally, a
variety of systems have been developed which
not only control, but also capture, landfill gas.
These more advanced gas control systems operate
using a network of pipes, wells, fans and/or
vacuums to provide a favourable migration route
to a common end point. Once collected, the gas
can be disposed of by flaring or recovered for its
energy value – it is a valuable fuel which has
added value due to its classification as a
renewable energy source under the Renewables
Obligation and so any electricity generated is
eligible for ROCs. It is estimated that around 63%
of landfill gas is currently flared or utilised – this
is forecast to rise to 72% in 2005.
155
Flaring
Flaring involves the collection of gas into a
chimney, where it is ignited in order to oxidise
methane to carbon dioxide prior to emission.
Flares are the simplest technology for the
prevention of methane emissions to the
atmosphere and are of two types: ‘open flame’
and ‘enclosed flame’. In an ‘open flame’ flare, the
gas is simply combusted on top of a flame burner,
with oxygen coming from the atmosphere. Such
combustion is largely uncontrollable and will
result in sub-optimal oxidation of the methane
and therefore emission to the atmosphere.
Conversely, in an ‘enclosed flame’ flare, the gas is
combusted in a chamber with both landfill gas
and airflow controlled to ensure optimum
efficiency (in excess of 99%) of methane
combustion.
26
All flares require a minimum concentration of
methane to operate. Stable ignition requires a
methane content of between 30 and 60%,
although special flare designs can accept lower
methane concentrations of 5-15%.
75
Methane
concentrations may be too low for the flare in the
early and late stages of a landfill’s lifecycle, and
also possibly at intermediate times due to
variable gas production rates over time. Under
such circumstances, the flare can be primed with
natural gas or propane, although the GHG
consequences of this are not ideal.
75
Energy recovery
Energy recovery is the conversion of waste to
produce useful heat or electricity. The methane
content of landfill gas makes energy recovery a
desirable option. One tonne of biodegradable
waste is thought to produce between 200 and
500 cubic metres of landfill gas with a calorific
value of up to 20 MJ per m
3
(5.5 kWh/m
3
).
101-103
In order to exploit this resource effectively, a
site must fulfil a number of requirements. In
particular, a site must generate a sufficient
quantity of landfill gas to make methane
combustion economically viable, which means
current projects are restricted to sites in receipt of
relatively large quantities of biodegradable waste.
The methane content of the gas must be
relatively high (at least 40%) and also consistent,
as fluctuations in methane concentrations can

43 Chapter 5: Waste and landfill
cause severe operational problems. In order to
avoid large variations in methane concentrations,
collected gas must be closely monitored and
adjustments made accordingly. For example,
over-pumping could introduce air into the landfill
site, reducing methane production. It is possible
to optimise a site for landfill gas utilisation, since
factors such as landfill temperature, moisture
content and pH can have a large impact on the
rate of landfill gas generation and composition.
Development of techniques such as recirculation
of landfill leachate also have the potential to
increase rates of waste decomposition and gas
generation.
77
If successfully implemented, such
developments will improve the viability of landfill
gas utilisation and may, in particular, improve the
prospects for projects on smaller sites.
Landfill gas is considered a renewable energy
resource
104
and therefore displaces greenhouse
gas emissions from energy derived from fossil
fuels. There are three main methods of utilising
landfill gas for its energy value: direct use,
electricity generation and purification. A fourth
option, the use of fuel cells, is still a relatively new
and expensive technology, but may become more
viable in the future.
Direct use
The direct use of landfill gas as a fuel (to generate
heat) is the most efficient energy recovery option,
utilising over 80% of the calorific value of the
methane. Piping the gas over long distances has
proven problematic and costly, therefore the gas
is most commonly piped directly to a local heat-
intensive industry, such as fuelling kilns, boilers or
furnaces. However, since landfill sites are
typically located away from population centres
due to the unaesthetic nature of waste disposal,
they are rarely located near such industrial sites.
This practice has worked best if the producer of
the landfill gas is also the user, so that supply and
demand are closely matched.
Electricity production
Landfill gas can be combusted to drive engines or
turbines for electricity generation. Fuel
conversion efficiencies typically range from 26%
(for gas turbines) to 42% (for dual-fuel engines),
which are comparable to conventional gas-fired
power stations. Production capacity varies from a
few kilowatts (kW) to several megawatts (MW).
75
The electricity generated can then either be used
directly or sold to the grid.
Since the 1980s, the landfill gas technology for
electricity generation has evolved dramatically
and the necessary equipment is now readily
available on the market. Landfill gas can also be
used to generate combined heat and power
(CHP), although this requires a use for the heat
close to the landfill site itself.
In 2003, landfill gas generated about 3.27 TWh
of electricity,
105
equivalent to 24% of renewable
electricity production in the UK and 1% of net UK
generation. Landfill gas is by far the largest single
source of new renewable electricity (i.e. excluding
large hydro plants) – by contrast, all the wind
farms in the UK generated just 1.3 TWh.
Purification to natural gas quality
Landfill gas can be cleaned to pipeline quality
(100% methane) and fed into the natural gas
distribution network. This process involves
removing the carbon dioxide and trace
contaminants from the landfill gas. The high
fixed costs of refining equipment and the
relatively low value of natural gas have precluded
the widespread uptake of this technology.
Fuel cells
A fuel cell is a device which converts a fuel
feedstock, usually hydrogen, directly into electrical
energy. Fuel cells that operate at high
temperatures, namely ‘solid oxide fuel cells’ and
‘molten carbonate fuel cells’, can utilise methane
directly.
One million tonnes of
landfill waste will be
adequate to generate
1MW of electricity for 10
years

44 Chapter 5: Waste and landfill
Fuel cells rely on expensive catalysts to
function, so the feedstock entering the fuel cell
must be free of impurities to prevent poisoning of
the catalyst. The purity required, in terms of
removing the trace elements, is even higher than
natural gas quality, which provides an additional
expense. However, fuel cells can operate at low
methane concentrations so carbon dioxide
removal is not a requirement for successful
operation.
Fuel cells are currently expensive and only a
few pilot projects exist for converting landfill gas
to electricity. However, they do offer some
significant advantages over other technologies.
The efficiency of fuel cells is currently around 40%,
which is higher than conventional heat engines.
Furthermore, nitrogen from air does not react in a
fuel cell, whereas it does in combustion devices, so
nitrogen oxides are not emitted. Fuel cells are also
a modular technology and so the size of the fuel
cell array can be adjusted to suit the output of the
landfill over time: as methane emissions decline,
fuel cells can simply be removed so that the
remaining stack is better matched to the supply of
methane. The removed fuels cells can then be
redeployed at other landfill sites.
Encouraging capture
Both flaring and energy recovery reap substantial
greenhouse gas emission savings by oxidising
methane and releasing only carbon dioxide. It is
estimated that 1.7 Mt of methane was abated in
2000, forecast to rise to 2.47 Mt in 2005.
155
The
degree of savings depends largely on the
efficiency of the gas collection system. No system
has yet been developed which completely inhibits
the release of landfill gas to the atmosphere. In a
modern landfill with a comprehensive gas
collection system, an average of 85% of the gas
will be collected,
25
whilst the remaining methane
will migrate through the capping layer where 90%
will be oxidised by methanotrophic bacteria en
route.
26
So, at a minimum, methane emissions
from new landfill will be just 2% of total
generated methane.
Emissions from pre-1996 sites (prior to
implementation of 1994 regulations) have been
shown to be negligible.
156
However, since landfill
sites generate significant methane for 15 to 20
years,
106
post-96 sites which have been closed
because they do not meet the regulations may
represent an important source of methane
emissions. The extent of this issue is unclear:
data on the number of landfill sites are uncertain,
as are data on methane emissions from these
sites. It is difficult to establish a firm baseline for
emissions from this sector since methane
concentration decreases over time due to natural
processes.
In 2002, only 211 landfill sites in the UK
extracted landfill gas for energy recovery
107
– a
very small proportion, given that there are 2300
working landfill sites in England and Wales alone.
The main incentive for methane capture in the UK
has been through ROCs under the Renewables
Obligation, which has improved cost-effectiveness
of landfill gas electricity production. As of June
2002, landfill gas utilisation contracts had been
awarded to around 10% of licensed sites in the
UK,of which around 60% (201 of 329) were
operational
108
(Table 13).
Table 13: Contracts under Renewables Obligation,
December 2001
Capacity (MWe)
Projects Projects
awarded live
England and Wales 653.4 384.6
Scotland 40.0 16.6
Northern Ireland 6.3 0
Total 699.7 401.2
Source: DUKES, 2003
105
Further growth is expected in the foreseeable
future, encouraged by the Landfill Directive, since
the resource potential is far from maximised. In
fact, the DTI estimates the UK landfill gas
resource to be equivalent to around 6.75 TWh per
year, over twice the generation in 2003 of 3.27

45 Chapter 5: Waste and landfill
TWh, and representing around 2% of present
electricity demand.
8
5.4 Alternatives to landfill
In order to comply with the Landfill Directive, in
combination with best-practice methane recovery,
alternative waste disposal methods are necessary
to reduce reliance on landfill. In effect, this means
progressing up the waste hierarchy towards more
sustainable waste management options.
UK Waste Strategy
The targets under the Landfill Directive pose a
tough challenge for the UK, exacerbated by the
current 3% annual growth in municipal waste.
70
Reducing the amount of biodegradable waste
disposed to landfill will require considerable
effort by the entire UK waste management chain,
including central and local government, waste
producers and the general public. Consequently,
the UK Government’s Waste Strategy 2000
97
has
been developed in accordance with the principles
of the waste hierarchy and wider sustainability,
with a strong presumption against sending waste
to landfill.
Under the Strategy, the Government has
established a number of other targets to
complement those for biodegradable waste
reduction. In particular, the following targets
have been established for the recovery of value
from municipal waste, via recycling, composting
and other forms of material and energy recovery:
•to recover value from 40% of municipal waste
by 2005;
• 45%, by 2010;
•67%,by 2015.
Recycling and composting
In addition to diverting biodegradable waste from
landfill, both recycling and composting enable
value to be reclaimed from the waste. Of the
biodegradable component, paper, wood and some
textiles can be recycled successfully, with the
resultant materials used in a range of products.
Food, garden waste and cardboard can all be
composted, with the residue forming a valuable
organic fertiliser.
Neither recycling nor composting avoid
greenhouse gas emissions. However, if managed
well, both options offer significant advantages
over landfill. Whilst recycling demands a
significant energy input, the associated
greenhouse gas emissions are relatively low when
compared to those offset from both the
production of virgin materials and disposal of
materials to landfill. Recycling is also pivotal to
resource conservation.
Composting is a largely aerobic process,
meaning that the major by-product of waste
decomposition is carbon dioxide. The majority of
the carbon remains within the compost, hence
giving it high value as an organic fertiliser.
However, the process must be well managed, with
the compost well mixed and regularly turned to
ensure sufficient aeration, else methane can be
generated under anaerobic conditions.
Composting has the advantage of being feasible
on a local level, for individual households, or as
community compost schemes. Large scale,
centralised composting systems tend to be
mechanised, although the sophistication of the
system can vary markedly. Highly complex
The UK has a target to
recycle and compost at
least 33% of household
waste by 2015

46 Chapter 5: Waste and landfill
systems may have the capacity for up to 100,000
tonnes of organic waste per year.
109
Both composting and recycling depend upon
separation of the waste. At the household level
this may require significant education of the
public, whereas on larger scales, labour is required
to perform an often unpleasant task. However,
mechanical biological separation schemes (see
below) may offer a viable alternative that does
not require separation of the waste stream.
Current situation
Recycling rates in the UK are currently amongst
the lowest in Europe at 9%,
97
although they are
increasing. Large scale waste composting is
growing at an exponential rate and doubled in
size in the two years to 2002.
110
Individual
households have practised small-scale
composting for many years and the UK
Government is encouraging this on a wider scale.
Under the UK Waste Strategy, there is
particular emphasis on improving recycling rates
in the UK. These efforts have included a focus on
producer responsibility, particularly with regard to
paper and packaging waste. Regulations have
been introduced which specify targets for the
recovery and recycling of packaging waste.
111
This
is supported by the 1994 EU Packaging Directive,
which aims to pass the responsibility for
packaging waste onto the producer thus
providing an incentive to minimise such waste.
The Government has also been working with
the Newspaper Publishers Association to increase
the recycled content of newspapers, which had
increased from 28% in 1991 to approximately 54%
in 1999. Targets were introduced to increase this
to 60% by 2001, 65% by 2003 and 70% by 2006.
The 2001 and 2003 targets were both met ahead
of schedule.
112
The Government is also working
with the Direct Marketing Association and other
trade bodies to reduce the quantity of junk mail,
which had more than doubled between 1990 and
1999, from 1.5 to 3.3 billion junk items per year.
Energy from waste
Energy from waste (or incineration) is seen as a
key technology for diverting waste away from
landfill sites and is widely used throughout
Europe. It is a well-developed technology, cost-
effective and makes use of the calorific value of
the waste material.
Energy from waste does not require the
separation of waste prior to treatment and, once
burned, the original volume of the waste is
typically reduced by around 70%.
26
The inert ash
residue is suitable for landfill and in some cases
may be recycled (e.g. for road surfacing). Energy
can also be recovered from the incineration
process for district heating or electricity
production. Interestingly, electricity generated
from incinerating mixed (biodegradable and non-
biodegradable) waste is not eligible for ROCs,
whereas energy generated from landfill methane
from the same initial waste feedstock is eligible
113
(Table 14). However, electricity from waste
incineration is exempt from the Climate Change
Levy.
The combustion of waste in incinerators does
not produce any methane, since carbon dioxide is
the main by-product of any efficient combustion
system. There has been concern about emissions
to the atmosphere of heavy metals and dioxins
from municipal solid waste incinerators.
114, 115
The
introduction of the Waste Incineration Directive
2000/76/EC alleviates this concern as it sets
stringent operating conditions and minimum
technical requirements for waste incineration and
co-incineration. The Directive is aimed at
Table 14: Financial incentives for electricity generation from waste streams
Technology Useful output RO eligible? CCL eligible?
Landfill CH
4
Yes Yes
Energy from waste Heat No Yes
Pyrolysis Oils, hydrocarbons, Biodegradable Yes
CH
4
fraction only
Gasification CH
4
,H
2
Biodegradable Yes
fraction only
Anaerobic digestion CH
4
Yes Yes

47 Chapter 5: Waste and landfill
preventing and limiting negative environmental
effects of emissions into air, soil, surface and
ground-water from the incineration and co-
incineration of waste, and the resulting risks to
human health.
Current situation
More than 9% of UK municipal waste is dealt
with by incineration.
116
Energy from waste
technologies are almost always used – just 0.3%
of waste is incinerated without energy recovery
and this value is falling. The UK incinerates a
smaller proportion of its municipal waste
compared to other European countries, such as
Denmark (52%) and France (24%).
117
However, despite the introduction of tighter
emissions controls, incineration is still socially
unpopular in the UK, with incineration schemes
attracting widespread opposition, especially at a
community level. This makes promotion of
incineration schemes a politically sensitive issue.
In addition, since any electricity generated is not
eligible for ROCs there is less financial incentive
to invest in this technology.
Advanced thermal treatment
Energy from waste is simply combustion of the
waste in an excess of oxygen, which generates
heat that may be used for electricity generation.
However, advanced thermal treatment methods
have been developed that also allow value to be
recovered from the calorific value of waste
materials. Advanced thermal treatment plants
are of two types – pyrolysis and gasification –
depending on the availability of oxygen and
temperatures reached. Pyrolysis heats the waste
to approximately 500ºC in the absence of air and
may be considered analogous to the formation of
charcoal. This process produces oils and gas
which may then be used as fuels in their own
right. Gasification is a higher temperature
process (1000-1200ºC) which partially combusts
Pyrolysis plants are found
in Europe but are not yet
widespread in the UK

48 Chapter 5: Waste and landfill
the waste in the presence of some oxygen. This
produces hydrogen and gaseous hydrocarbons
which may then be combusted as a fuel.
Unlike energy from waste, advanced thermal
treatment plants do require the separation of
waste prior to entering the plant. Recyclable
materials such as glass and metals are removed
before entering the plant. Post treatment, the
flue gases are scrubbed to remove particulates
and higher hydrocarbons before using the gases
as fuel. Advanced thermal treatment plants are
comparatively small as they deal with only
specialised sections of the waste stream. They
can also act as a modular component for a larger
waste plant, such as mechanical biological sorting
plants.
Electricity generated from by-products of the
advanced thermal treatment of waste is eligible
for ROCs. However, only the fraction generated
from biodegradable waste is eligible, so the
financial returns will be dependent of the
composition of the waste entering the plant
113
(Table 14).
Current situation
There are currently no demonstrated advanced
thermal treatment facilities in the UK other than
on a pilot scale.
154
Anaerobic digestion
Fully-optimised anaerobic decomposition of
waste is possible using purpose-built anaerobic
digesters in a process known as biogasification. A
wide range of biodegradable waste can be treated
in this way, including wastes that are unsuitable
for composting, such as meat and cooked food.
Typically, biodegradable waste is separated from
other material before digestion, either manually
or mechanically, although newer mechanical
biological separation plants can avoid this
requirement.
Anaerobic digesters can reduce the time it
takes for waste to fully degrade from a few
decades to a few weeks, hence maximising the
production of methane over a shortened time
period.
26
Because anaerobic digesters are
enclosed systems, more methane can be
recovered, enhancing the efficiency of the system
and allowing maximum value to be recovered
from the waste stream. The use of anaerobic
digesters also yields a more regular and sustained
supply of gas compared to landfill. Between 10
and 50% more methane is produced per tonne of
waste (depending on waste composition and
digester design) than if sent to landfill, yet
emissions are typically 1% or less.
26
The gate fees
charged for taking the waste are the key
economic driver behind this technology. The
biogas may be burned as a fuel and is eligible for
ROCs, providing an additional financial driver for
investment (Table 14).
113
Greater efficiency also
means that large areas are not required, although
a sizeable industrial-style plant must be built. In
addition to the valuable methane, the process
also produces a solid digestate, which can be used
to improve soil quality, and a nutrient rich liquid
residue, which can also be applied as a fertiliser.
Current situation
In contrast to countries like Denmark, which uses
anaerobic digestion to treat about 1.1 Mt of waste
per year, this method is less common for waste
disposal in the UK.
118
Sewage sludge and
agricultural wastes have been treated by
anaerobic digestion for several years, but the
process is now slowly extending to municipal
solid waste with a small number of plants in
operation, each of which can handle
approximately 260-300 tonnes of waste per
year.
118
Encouragement to invest in such schemes
already exists in the form of the waste gate fees
and ROCs.
113
However, as a relatively unproven
technology in the UK, additional support through
grants or subsides may be necessary to stimulate
the market.
Mechanical biological separation schemes
Several commercial mechanical biological
separation schemes have been developed in the
UK to recover value from all parts of the waste

49 Chapter 5: Waste and landfill
stream. In each case, the initial stage is to shred
the municipal waste into small pieces. Biffa’s
integrated waste management process separates
the biodegradable waste at this stage and sends
it to an anaerobic digester. Conversely, Shanks’
Intelligent Transfer Station passes all waste into
an aerobic digestion chamber, which rapidly
degrades biodegradable waste. Value is recovered
from the rapidly biodegradable component in the
form of methane and then energy. The waste
material from both systems is dry, clean and
sterile and can be sorted into component
materials, with ferrous and glass materials
recovered for recycling. Approximately 50% of the
waste material, mainly cardboard and plastic, is
only slowly biodegradable and is not removed by
the digestion process. This material has a high
calorific value and can be used as a secondary fuel
in fossil fuel combustion plants capable of co-
firing, where it counts as a renewable energy
resource (as far as the UK’s 10% target is
concerned) and is exempt from the Climate
Change Levy. Renewable Obligation Certificates
can also be obtained if the plastic portion of the
fuel is not too high.
119
Current situation
As with anaerobic digesters, there are only a few
of these schemes currently in operation in the UK.
Gate fees and ROCs could provide the incentive
for further investment in this area. This method
of waste disposal is highly flexible and will be
able to cope with the changing waste
composition over the next 20 years.
5.5Recommendations
Data uncertainties
Landfill sites are a major source of methane
emissions, with significant methane generated
for at least 15 to 20 years at any one site.
However, there is uncertainty as to the extent of
this problem due to lack of data on the exact
number of landfill sites in the UK and associated
methane emissions. Although it is impossible to
predict how much methane is actually produced
within a landfill site, the quantity of gas captured
is easy to measure.
A comprehensive inventory of UK landfill sites,
both working and closed, detailing the type of
capping layer and other methane capturing
technologies installed and amount of gas
captured, is needed. This is particularly important
for older and closed sites which are unlikely to
utilise modern technologies and so could
represent a significant source of emissions.
Policy
For maximum savings in this area, there needs to
be a stronger policy focus on methane mitigation,
as in the EU Landfill Directive, rather than relying
solely on achieving emissions reductions
indirectly through waste reduction policy.
Methane capture
The energy content of waste should be recovered
wherever possible. Encouraging and supporting
the installation of suitable methane recovery
technologies is central to the Landfill Directive.
The crucial issue is how this will be implemented
in practice. The Renewables Obligation has been
a key driver in encouraging energy recovery from
methane in the UK by providing an economic
incentive to capture as much of the generated
methane as possible, relying on market-based
mechanisms. This could be underpinned by the
provision of grants or subsidies by the
Government to encourage the uptake of best-
practice technologies.
Lower production volumes of methane from
landfill in future years (assuming the Directive is
successful) would open up the way for new
landfill gas technologies capable of operating at
lower concentrations, such as fuel cells, provided
there are sufficient economic incentives to attract
investment. Grants or subsidies from the
Government would encourage the development
of such technologies.

Alternatives to landfill
If biodegradable waste is to be diverted from
landfill, as required by the Directive, support must
be given to viable alternatives (without
associated methane emissions) for the disposal of
this waste. Given the political sensitivities around
incinerators in the UK and the lack of a strong
financial incentive in the form of ROCs,
incineration looks to be a less politically favoured
method of waste disposal. Anaerobic digesters
and mechanical biological separation schemes
appear to be more attractive options, with the
waste gate fees and eligibility for ROCs providing
economic drivers for investment. As with the
methane capturing technologies, the introduction
of these schemes could be further encouraged
through the provision of grants or subsidies.
Waste reduction
Waste reduction still has an important role in
reducing methane emissions. The problem here is
not really the lack of relevant policies but merely
a problem in implementation of existing policies.
The UK Government’s primary concern,
particularly for municipal waste, is to move up the
waste management hierarchy towards waste
avoidance and minimisation. This requires action
by manufacturers, to reduce packaging, and local
councils, working with their residents to achieve
widespread changes in lifestyles and attitudes.
Conflict with the Renewables Obligation
In the UK, the Renewables Obligation is one of
the key drivers behind investment in methane
recovery technologies through the provision of
ROCs. However, the Landfill Directive also aims to
reduce the amount of biodegradable waste sent
to landfill. This will result in less methane being
produced and so the financial rewards from
generating electricity from landfill gas will be
lower. Hence, there is a danger that the incentive
provided by ROCs to introduce best-practice
Anaerobic digestion of
waste generates electricity
without any methane
emissions
50 Chapter 5: Waste and landfill

51 Chapter 5: Waste and landfill
capturing and electricity generating technology at
landfill sites will be lessened and other incentives
may be needed in the future. However, there will
be a significant delay before the impacts of
biodegradable waste reduction are felt, since
current landfill sites will continue to produce
methane for tens of years.
Trading
Two possibilities exist for trading in the waste
sector: trading the actual waste itself and trading
of methane emissions from landfill.
Trading of waste
The opportunity of trading waste is currently
under consideration in the UK. The system of
biodegradable waste trading is a system,
underpinned by the Waste and Emissions Trading
Bill, which would enable waste disposal
authorities to meet the objectives of the Landfill
Directive and thus reduce methane emissions at
minimum cost. Operating on a system of
tradable allowances, those authorities that
exceed their allowances by sending less
biodegradable waste to landfill will be able trade
the excess allowances with those that send
more.
120
Such a policy tool will certainly help
meet the targets set out by other waste policies
such as the Landfill Directive.
Methane trading
In terms of trading, the possibilities from landfill
sites are limited since methane capture is already
required at all sites for safety reasons, with best-
practice technology specified for new sites under
the Landfill Directive. None of the methane
savings would be ‘additional’ and are therefore
not tradable. Similarly, diversion of waste from
landfill to reduce methane emissions is not a
viable route into the trading process either as this
is also required under the Directive. Poor capping
technology at older landfill sites may result in
higher methane emissions and so any further
reductions would count as additional. However,
there is no easy way to capture the methane that
leaks out through the cap – retrofits are not
possible. Even if there were methane available to
trade, because the market price of ROCs is
currently higher than that of methane, obtaining
ROCs would be the preferable option, thus
removing the incentive to trade.

52 Chapter 6: Agriculture
Agriculture is responsible for 43% of methane
emissions (0.91 Mt) making it the largest
methane-emitting sector in the UK.
63
Emissions
arise entirely from the livestock sector, almost
90% of which are a direct result of the digestive
processes in livestock mammals
121
(enteric
fermentation). The remaining 10% arises from
manure management practices which promote
anaerobic decomposition of waste. Non-livestock
agriculture is not a measurable source of
methane in the UK.
Emissions from the agricultural sector are
declining slowly, being 13% lower in 2002 than
1990. This is not so pronounced as emissions
reductions achieved by other sectors. As a
consequence, the relative importance of methane
emissions from agriculture has grown. Policy
measures will be required to achieve substantial
cuts in emissions, but implementing such policies
is a major challenge.
The UK livestock industry has suffered greatly
in recent years, with both the BSE (bovine
spongiform encephalopathy) and Foot and Mouth
crises damaging consumer confidence and
profitability of farms. The UK farming industry is
regarded by the public as a vital component of
the UK economy, so any policy measures
introduced must reflect this and not penalise an
already strained industry. Furthermore, there is
public mistrust of the effects of agri-technologies
and large scale agri-business, as exemplified by
BSE, Foot and Mouth, and genetic engineering.
Any mitigation measures actively promoted by
the Government should reflect these concerns.
6.1 How is methane produced?
Methane emissions from the agricultural sector
derive from two sources: enteric fermentation and
manure management practices (Table 15).
Enteric fermentation
Methane is produced as a result of the natural
digestive processes in ruminant mammals (those
that chew the cud), such as cattle and sheep.
Unlike humans and other non-ruminant
mammals, ruminants are unable to digest their
feed entirely, particularly cellulose-based plant
polymers, by the action of stomach enzymes
alone. Instead, ruminants have an expanded gut
(the retrulo-rumen) in which feed is broken down
by bacteria and ferments prior to gastric
digestion. In an adult ruminant, the rumen
comprises approximately 85% of the stomach
capacity and typically contains digesta equivalent
to around 10-20% of the animal’s weight.
26, 123
Food is retained in the rumen for a
considerable period of time where, in the
presence of a large and diverse microbial
population, it is anaerobically fermented to form
volatile fatty acids, ammonia, carbon dioxide,
methane, cell material and heat (Figure 17). The
balance of these products varies between animals
and with dietary intake, being largely determined
by the composition and activity rates of micro-
organisms present in the rumen. The gaseous
waste products are mainly removed by the
process of eructation (burping) or eliminated as
part of the respiration process.
124
Less than 10% is
emitted as flatus (farts).
Agriculture
Table 15: Methane produced by enteric fermentation and manure management
(kg methane per head per year)
Animal Enteric fermentation Manure management
Dairy cows 115 13
Beef 48 6
Other cattle > 1yr 48 6
Other cattle < 1yr 33 6
Pigs 1.5 3
Sheep 8 0.2
Lambs < 1 yr 3.2 0.1
Goats 5 0.1
Horses 18 1.4
Poultry Not estimated 0.1
Deer 10 0.3
Source: National Atmospheric Emissions Inventory, 2004
122

Figure 17: Enteric fermentation in ruminant
mammals
Non-ruminant mammals do produce some
methane as a result of digestive processes, but at
far lower rates. For example, pseudo-ruminants
(such as horses) do not have a rumen, yet ferment
feed during the digestive process to enable them
to obtain essential nutrients from plant material.
Mono-gastric animals (such as pigs) also produce
small quantities of methane during digestion.
Manure management
Modern manure management systems tend to
restrict the availability of oxygen to the waste,
promoting the production of methane. Anaerobic
manure management is associated with intensive
agriculture, particularly dairies and pig farms
where large numbers of animals are contained
within a single, relatively confined facility. The
high density of animals leads to the production of
large quantities of waste, which is typically
washed out into tanks, lagoons or pits where it is
stored as a liquid or ‘slurry’. Being liquid, air is
excluded and waste decomposition takes place
under predominantly anaerobic conditions,
resulting in the production of methane.
The amount of waste produced is dependent
upon the number and types of animals, along
with the quantity and quality of food consumed.
The precise amount of methane produced from
any given animal waste is dependent upon a
number of factors, most notably the quantity and
composition of the waste, which, in turn is
dependent upon the type of animal and feeding
practices. Ambient climatic conditions are also
important. Increased temperature promotes
biological activity, thereby enhancing methane
production.
Emissions from livestock are a diffuse source and
as such are not easily captured or quantified.
Therefore mitigation strategies for this sector
focus on reducing production at source. Methane
production from animals is dependent on a
number of factors, represented simply as:
Total emissions =
Number of animals
x Lifetime of animal
x Emissions per head per day
The overall emissions may be reduced by altering
any of the above parameters: reducing livestock
numbers, reducing the emissions per animal, or
achieving the same product yields over a shorter
lifetime. There is a range of management and
technological options available, some of which
will alter more than one of these parameters at
once.
Methane from animals is a waste product,
representing a loss of dietary energy available to
the animal of 2-12%. As such, the production of
methane both directly from enteric fermentation
and from the decomposition of organic animal
waste, is a reflection of the inefficiency of the
digestive process. Consequently, methane
emissions can be reduced through productivity
improvements, which also offer potential cost-
benefits to the agricultural sector. Increased
productivity can be achieved through increasing
the yield of meat or milk from an animal over the
same lifetime, or attaining the same yields in a
53 Chapter 6: Agriculture
6.2 Mitigating emissions from
livestock

54 Chapter 6: Agriculture
shorter lifetime. Both have the effect of reducing
the overall methane production per mass of
product. This requires nutritional adjustments,
such as changes in diet and use of feed
supplements, or genetic modifications. These
options are discussed in more detail below.
However, the applicability of these techniques in
practice is limited by a number of factors, namely:
risks to human health; consumer acceptability;
animal welfare issues (particularly risks to animal
health and development); ethical considerations;
and cost effectiveness.
Dietary adjustments
Improved nutrition and dietary adjustment in
order to optimise rumen and animal efficiency is
a growing area of interest in terms of both
environmental and productivity benefits.
Methane emissions depend on the average daily
feed intake and efficiency with which feed energy
is converted into product (meat, milk). This in
turn depends upon the efficiency of rumen
fermentation and the quality of the feed.
Improvements to the quality of animal feedstuff,
particularly in terms of digestibility and energy
value, or improvements to rumen efficiency
provide two potential routes to methane
reductions.
Feed quality
Feed conversion efficiency – the rate at which
feed energy is converted into product rather than
waste – is higher for certain types of feed. For
example, grain feeds are converted more
efficiently than forages (grass), as they are
relatively easy to digest and have a high energy
content.
Rumen efficiency
Efficient digestion requires a diet that contains
essential nutrients for the fermentative micro-
organisms. If nutrients such as ammonia,
sulphate and phosphate are limited, digestive
efficiency will diminish, resulting in increased
emissions of methane. Nutritional supplements
can therefore be used to enhance dietary
nutrition. In some cases this has resulted in
increased milk yields of 20-30% and increased
growth rate of 80-200%,
26
with typical methane
reductions of up to 40% per unit output. The
largest gains from nutritional supplementation
are likely to be amongst animals on low quality
feeds: in tropical areas with chronic feed
constraints, supplements can result in emission
reductions of up to 75%. In the UK, where
ruminants have relatively high quality diets, this
potential is more limited. Nevertheless, a number
of advanced supplements, in the form of chemical
and pharmaceutical additives, have been
developed which have the potential to deliver
further efficiency or productivity improvements.
This may not prove a popular option given the
growing consumer backlash against the use of
chemical additives in recent years and a number
of such substances have already been prohibited
from use in the EU and elsewhere.
The extent to which dietary adjustments and
supplements could achieve methane reductions
in practice is largely dependent on the real and
perceived risks to human and animal welfare,
along with the economic cost.
Genetic improvements
Selective breeding can result in significant
improvements to the genetic characteristics of
ruminants, such as digestive efficiency and
productivity, although developments have been
hindered by associated problems with fertility,
lameness, mastitis and metabolic disorders.
26
Arguably, greater scope exists with improvements
to reproductive efficiency, which could
significantly reduce the large numbers of animals
which typically comprise a reproductive herd. The
UNFCCC (fact sheet 271) reports that pilot projects
in India have achieved increased birth rates as a
result of improved feeding practices: the interval
between births was reduced by almost half, from
24 months to 12-15 months. There have also been
suggestions that genetic engineering could
achieve methane reductions from ruminants by

55 Chapter 6: Agriculture
increasing fermentation efficiency through
adjustments to rumen micro-organisms.
However, there remains strong public
resistance to genetic engineering in the food-
chain due to both ethical objections and scientific
uncertainty regarding associated risks and knock-
on effects.
Reducing livestock numbers
Fewer animals will result in a reduction in
methane emissions from both enteric
fermentation and manure management.
However, this is a highly contentious and
politically troublesome option, especially after the
BSE and Foot and Mouth crises have strained the
UK livestock farming industry. Attempts to force
a reduction in livestock numbers are unlikely to
be successful; in New Zealand, proposals to
introduce a tax on livestock to reduce emissions
proved so unpopular the measure was
withdrawn. Any drop in numbers would also
need to be matched by a corresponding drop in
consumer demand for meat and animal products,
otherwise production and methane emissions will
merely be displaced to other countries.
There are signs of a shift in consumer
preferences with a change in demand for meat
and animal products. Within the UK, as well as a
number of other European countries and the USA,
there has been a noticeable move away from red
meat towards poultry, along with a growing
vegetarian movement and support for organic
produce. Whilst this has been greeted
optimistically by some in terms of the wider
implications for sustainability, including potential
greenhouse gas emissions reductions, the true
benefits remain unclear. In particular, the stability
of this trend, the wider implications for the
economy and agricultural sector, and the complex
knock-on effects for the environment and
sustainability are uncertain. Because of the
relative emissions factors (Table 15), minimising
consumption of dairy products is more significant
than minimising meat consumption, in terms of
greenhouse gas emissions. However, this would
be a difficult area to legislate.
Organic farming requires lower livestock
densities through tighter controls on animal
welfare standards. An individual farm turning
organic would therefore have to reduce stock
numbers to comply with these standards, but
would retain income due to the premium paid by
consumers for organic produce. However, this
may not reduce livestock numbers across the
whole agricultural sector if other farmers increase
their herds in order to supply the same level of
consumer demand for meat and milk.
Therefore, neither enforced reductions in
agricultural production levels or consumer
demand are considered to be realistic or viable
routes to long-term methane emission reduction.
Reductions in methane emissions from manure
decomposition can be achieved simply by
modifying waste management practices. Several
waste management techniques are available
which favour aerobic decomposition.
Dry deposition
The ‘dry deposition’ (land application) of waste is
a widely practised, relatively low-tech option,
which enables value to be recovered from waste
as a fertiliser. In order to minimise any
opportunity for anaerobic decomposition, the
manure needs to be spread as soon as possible
There is widespread
opposition to genetic
engineering in the food
chain
6.3 Mitigating emissions from manure
management

56 Chapter 6: Agriculture
following production and collection. The IPCC
report that, for the average EU climate, daily
spreading of manure results in the release of 0.1
to 0.5% of the manure’s methane potential
compared to 10 to 35% from conventional manure
management practices.
26
However, land
spreading of waste is not without problems. In
particular, this practice is associated with
relatively large ammonia and nitrous oxide
emissions and risks eutrophication of nearby
lakes and rivers from nutrient-rich run-off.
Composting
Composting offers another low-tech option for
managing manure. Liquid waste can be dried,
making the waste suitable for composting. If
necessary, other dry organic material can be
added to the waste. However, for air penetration
to be maximised, and therefore anaerobic
decomposition minimised, the compost must be
regularly turned.
In the case of both dry deposition and
composting, the complex organic compounds
within animal waste are broken down naturally
by bacteria, releasing carbon dioxide. This is part
of the natural carbon cycle, the carbon dioxide
being originally absorbed by the plants used as
livestock feed during photosynthesis. However,
both techniques are likely to require energy input
(for the mechanised processes) and therefore any
associated greenhouse gas emissions should be
deducted from the total methane savings. These
options may not be appropriate because they
both require a certain amount of space; methane
emissions from manure management are
generally associated with intensive farming
facilities dealing with large quantities of waste
within a confined area.
Aeration of liquid waste
A more practical way of reducing methane
production may be through the aeration of liquid
waste. By increasing the levels of dissolved
oxygen within liquid waste, typically using
mechanical pumps, aerobic decomposition is
encouraged. Again, this process requires
substantial energy input, with implications for
greenhouse gas emission savings. Furthermore,
this process has been linked to increased nitrous
oxide emissions.
Methane capture
In reality, it is often preferable to capture
methane emissions from the manure
management practice rather than attempt to
prevent them. Technologies to capture and
dispose of methane arising from manure
management practices are similar to those
applied to landfill and have proved highly
successful. Waste pits or lagoons can be lined and
covered with impermeable materials in order to
contain and collect the methane. Whilst this
option has the advantage of being relatively
low-tech, it does require space and the gas
capture rate may be fairly low due to problems
associated with sealing large areas.
Anaerobic digestion
A better rate of methane capture is achieved by
purpose-built anaerobic digesters, which operate
according to the same principles as those used
within the solid waste management process,
optimising decomposition of manure for methane
production and collection. The IPCC report that
anaerobic digesters typically release just 5% of
the total methane potential of the waste, most of
which comes from further decomposition of the
waste residue once it has been removed from the
digester.
Digesters have become increasingly popular
within the agricultural waste sector, bolstered by
the range of benefits offered by this technology.
By heating the vessel to around 60ºC, the
production of methane can be maximised over a
relatively short period, decreasing retention time
of the manure from around 60 to 20 days. The
biogas generated can be recovered for its energy
value, improving the cost effectiveness of this

57 Chapter 6: Agriculture
practice. The resultant gas comprises
approximately 65% methane, which can either be
combusted directly as a local source of fuel or else
used to generate electricity for use onsite or for
sale to the grid. This process ensures that
methane is converted into carbon dioxide prior to
emission and also offsets greenhouse gas
emissions from the equivalent energy supply
from coal or oil. Furthermore, the electricity
generated is eligible for ROCs, providing an
important financial incentive to implement
digester technology as well as being an additional
revenue stream for the agricultural community.
Other benefits of managed anaerobic
digestion include reduced contamination from
runoff, removal of noxious odours, lower levels of
pathogens and retention of the organic nitrogen
content of the manure. This means that the
residue is a valuable organic fertiliser. Other
products contained within the effluent have been
successfully used for animal feed and as
aquaculture supplements. Such advantages may
make anaerobic digesters an attractive option
even if energy recovery is not possible. In these
cases, the collected gas can be flared prior to
emission, oxidising methane to the less potent
carbon dioxide.
The UK’s first dung-fired power station is in
Holsworthy, Devon. It collects 146 000 tonnes of
slurry per year from 27 local farmers and has a
capacity of 1.4 MW, with the waste heat used for
a community heating scheme. The project was
relatively cheap, receiving £3.5m in EU grants,
coupled with matched funding from a German
biogas company. The intention is to introduce 100
such plants across the UK.
125
6.4 Existing EU and UK policy
There is currently no agricultural policy in the UK
specifically targeted at mitigating methane
emissions. Reductions in emissions have been
achieved fortuitously through policies aimed at
other objectives, such as nitrate pollution and
manure management.
Most UK agricultural policy is based on the EU
Common Agricultural Policy (CAP). Introduced in
the 1960s, the CAP was intended to decrease
dependence on imports and deliberately increase
domestic food production through a system of
subsidies paid to EU farmers. Other mechanisms
used by this policy were market management to
decrease surpluses, and import taxes and export
subsidies to protect the domestic market, thus
ensuring food security and a fair standard of
living for those dependent on agriculture. The
subsidies have resulted in some overproduction,
often at the expense of the environment, by
encouraging a more intensive form of agriculture
and so adversely affecting the amount of
methane produced.
The policy is also expensive, costing the EU
£28.5bn per year. It has been estimated that every
head of cattle in the EU is subsidised by £1.40 per
day.
126
The UK receives 9% of available CAP funds
(some £3bn in 2000-2001), but overall is a
significant net contributor to the policy.
127
The CAP is currently undergoing major
reform
127
as it is considered unsustainable in its
present state. These reforms are unlikely to
reduce costs but may decrease methane
emissions by reducing livestock numbers. The EU
has suggested ‘decoupling’ direct payments to
farmers (or separating payments from production)
so that farmers are encouraged to farm for market
demand rather than the subsidies available.
Removal of subsidies should lead to higher prices
and preserve farm income. Studies investigating
the impact of decoupling indicate that the recent
proposals will result in reduced agricultural
production and livestock numbers.
128-130
A further
reform of arable and dairy market regimes will
reduce intervention price support while partially
compensating farmers for income loss through
increased direct payments.
131
This is likely to
further reduce livestock numbers and therefore
methane emissions.
Another policy that influences emissions from
the agricultural sector is the Integrated Pollution
Prevention and Control (IPPC) Directive discussed

58 Chapter 6: Agriculture
in Chapter 5. This Directive extends the pollution
control regime to the UK agriculture sector by
covering intensive pig and poultry installations.
Again, this policy does not specifically target
methane, its focus being more on reducing
ammonia, but since it covers manure
management and production, it will also have
some impact on methane emissions.
6.5 Recommendations
Whilst the agriculture sector is responsible for the
majority of methane emissions in the UK, it is
also one of the most difficult in terms of
emissions reduction legislation, reflected in the
current lack of such policies.
Emissions from livestock
Methane capture is not a realistic option for
livestock emissions. Of the options for reducing
emissions, neither lowering livestock numbers nor
promotion of agri-technologies appear to be
particularly attractive or feasible politically.
Policies must be acceptable to the UK farming
industry and publicly acceptable in terms of food
safety and other environmental issues.
Reducing livestock numbers via direct policy
measures would be unacceptable to the farming
industry, who would view it as a loss of income. It
is possible that the CAP reforms may help to
reduce livestock numbers through the removal of
subsidies thus preventing overproduction,
although to what extent is unclear.
The current social trends towards organic
produce, lower meat consumption and
vegetarianism could help underpin any reductions
in animal numbers, although they are unlikely to
be major factors by themselves. Such trends
could be encouraged through educational
programmes focused on lower red meat and
(especially) dairy consumption, linked to the
corresponding environmental and greenhouse
gas benefits.
Organic farming is a farming system that best
addresses many policy objectives for agriculture
and has a strong growth potential given
continuing consumer demand. Supporting a
move towards more sustainable methods of
farming may help towards decreasing livestock
numbers.
Policies encouraging emissions reductions
through improving livestock productivity and
efficiency may find support amongst the
agricultural community due to increased profits.
However, such policies are unlikely to be popular
with the public, who, in general, wish for a more
natural form of agriculture with a minimum of
chemical or biotechnological inputs into the food
chain. The widespread rejection of genetic
engineering in this country and Europe, coupled
with fears over food safety following the
agricultural practices that led to the BSE crisis,
mean that any direct promotion of such measures
to reduce methane emissions are likely to be
viewed with distrust.
Further research is required into the
opportunities for productivity increases and
methane emission reductions from animal dietary
changes. This should be conducted within animal
welfare guidelines, taking into account public
acceptability of agri-technologies such as genetic
engineering.
In essence, as far as agricultural emissions
from enteric fermentation are concerned, there is
a trade-off to be made. Some reductions will
occur as part of the CAP, but any further
reductions in methane are likely to be difficult to
achieve without alienating the farming
community or the general public. Faced with
such an impasse, it may be necessary to accept
that the livestock industry is sufficiently
important to the UK and that a certain level of
methane emissions will always be produced by
agriculture. This shortfall can be made up by
simpler, more cost-effective reductions in other
methane generating sectors.

59 Chapter 6: Agriculture
Manure management
Policies targeted at reducing methane emissions
through improved manure management practices
are more straightforward. In this case, the
methane is capturable and therefore can be used
to generate electricity or fuel gas-fired
equipment. Best-practice technology exists in the
form of anaerobic digesters and a strong financial
incentive to support this technology is already
available through ROCs.
The main barrier to widespread
implementation at present appears to be lack of
knowledge about the technology or conservatism
within the sector. This could be overcome
through education of the farming community
about the positive benefits of anaerobic
digestion, further supported by grants or long
term low-interest loans to reduce the initial costs
of capital equipment, similar to those under the
Clear Skies Programme. Assistance in setting up
farming co-operatives with shared digester
facilities would also aid the development of
community level anaerobic digestion schemes.
Methane trading
Trading of emissions from livestock is unlikely due
to the scattered and diffuse nature of methane
producers, making capture difficult. Emissions
from this sector are hard to quantify, being based
on estimates of emissions factors from different
animals and feedstocks. Verifying any emissions
reductions would also prove complicated.
A further barrier to trading from the
agricultural sector is the small size of players –
traders require larger quantities than individual
farmers would be capable of producing. Such
players would therefore not be capable of
participating effectively in a trading scheme,
especially the EU Emissions Trading Scheme
which focuses on large scale emitters. Some form
of aggregation would be necessary, but this
would be likely to be so complicated as to be
ineffectual.
Food supplements and
growth hormones can cut
methane emissions. But do
the public want them?

60 Chapter 7: Oil and gas sector
7.1Introduction
The oil and gas sector was responsible for 0.39 Mt
(19%) of methane emissions in the UK in 2002,
63
making it the third largest methane-producing
sector. Emissions are from two major sources –
venting of methane from rigs and plants during
maintenance and leakage from the gas pipeline
network. Of these, the latter is by far the most
important, accounting for 85% of methane
emissions from this sector in 2001.
68
Importantly,
venting from rigs is a point source and therefore
capturable, whereas leakage from the pipeline
network is a diffuse source of methane and
therefore can only be reduced, not captured. This
is reflected in the large uncertainties of emissions
estimates from pipeline leakage (±40%).
Since 1990, the overall consumption of gas in
the UK has nearly doubled, rising from 597 TWh
to 1104 TWh in 2003
105
(Figure 18).
The increased throughput of gas since 1990 is
mainly due to an increase in gas-fired power
stations, rather than an increase in domestic and
industrial usage, which have remained roughly
constant. With the decline of nuclear power
coupled with increased electricity demand, gas is
likely to form an increasing contribution to UK
electricity generation in the foreseeable future.
Therefore methane emissions associated with this
sector are becoming progressively more
significant.
7.2 Sources of methane
Pipeline leakage
In 2003, it was estimated that 4.5 TWh of gas was
lost through leakage.
105
Leakage from pipelines is
difficult and costly to eliminate. Individual joints,
flanges and seals along the distribution network
leak frequently and, although not a major source
of methane individually, are cumulatively
significant over the whole 275,000 km pipe
network.
62
Leakage is greater from traditional
cast iron pipes than modern plastic versions.
132
Most of the methane leakage, perhaps tens of
tonnes per year, is from compressor seals in the
boosters which are required every 60-100 miles
along the pipe network to maintain pressure for
transmission. Valve leakage can be very high in
older installations.
132
Venting from rigs
Methane may be mined independently as natural
gas or alongside oil and coal. In 1998, there were
a record 204 offshore oil and gas fields in
operation (Figure 19). Of these, 109 were
producing oil, 79 gas and the rest condensate (a
liquid condensed from natural gas).
133
In total, 127
million tonnes of oil and 103 Mt oil-equivalent of
natural gas were mined in 2002.
105
When oil is mined from a rig, it contains a
mixture of oil, water and natural gas. This is
separated on site by passing the mixture into
large settlement tanks, where the three fractions
separate by gravity. Gas is removed at the top
and water from the bottom, leaving just the crude
fraction. After repeating this process several
times, the oil is of high purity and can be pumped
along a pipeline to shore.
When the tanks need maintenance they must
be made safe for human activity; methane is both
explosive and a non-pungent asphyxiate. The
Oil and gas sector
Figure 18: Gas consumption by sector, UK, 1970-2003
Source: DUKES 2004
105

tanks are sealed off and flushed with water, then
nitrogen, followed by air. The latter processes
purge methane from the tanks, which were
historically vented to the atmosphere. This
resulted in significant methane emissions,
especially due to the high operating pressure.
Gas only rigs must also be purged of methane
before work can recommence.
134
7.3Mitigating methane emissions
Pipeline leakage
As a diffuse source of methane, capture is not an
option. Mitigation of methane emissions from
the pipeline network can be achieved simply by
replacing old cast iron pipes with modern plastic
piping. However, this is a laborious and costly
process, involving labour-intensive construction
work. Despite gains in operating efficiency to be
made by minimising leaks, the relatively low cost
of gas, especially compared to the cost of
upgrades, means there is little economic incentive
to do so. Even with the likely rise in gas prices
over the coming years as the UK becomes more
reliant on fossil fuel imports, fuel price alone is
unlikely to encourage network investment.
Venting from rigs
As a point source, capturing methane from rigs is
more straightforward. By flaring instead of
simply venting to the atmosphere, carbon dioxide
is emitted in place of the more potent methane.
This tends to be the most common method used
to deal with the methane. Alternatively, all
greenhouse gas emissions can be avoided by
passing the aqueous and gaseous by-products
from the tank back into the well during
maintenance, thereby sequestering the
greenhouse gases that would otherwise be
emitted to the atmosphere. This methane does
not remain sequestered: it is mined again when
the rig is operational once more.
134
7.4Existing UK policies
In the UK, there are few policies or regulations in
place that address natural gas leakage from pipes
or even leakage monitoring. National Grid
Transco operate the pipeline network and are
responsible for its maintenance and attending to
leaks. Transco spends an average of £600m per
year on maintenance, of which £335m is spent on
pipeline replacement. Transco is also mandated
by the Health and Safety Executive to replace iron
pipelines that lie within 30m of any property; a
programme that will take place over 30 years.
This, however, is a safety issue rather than active
greenhouse gas abatement.
Leakage rates from the natural gas
transmission and distribution network have
improved as a result of a number of efforts:
replacing old cast iron pipework, gas conditioning,
pressure management and a mains and service
replacement programme.
135, 136
Emissions have
reduced by 14% (for the period 1990-2001)
135
against a target of 20% by 2000 (relative to 1992
levels).
136
In line with this, Transco revised its
internal target to reduce leakage, in absolute
terms, by 12.5% from 1990 levels by the year 2010,
citing increased throughput as the reason for
revision of the 20% target. It does, however, aim
to overachieve this target by 7.5% by that date.
136
Encouraged by the UK Emissions Trading
Scheme (UK ETS), significant advances have been
made in reducing methane emissions from oil
and gas rigs. Companies such as Shell and BP
have been able to trade carbon credits gained
from capturing methane that would have
otherwise been released into the atmosphere.
Both BP and Shell have also developed their
own internal trading schemes in advance of both
the UK and EU ETS. Pilot trading of greenhouse
61 Chapter 7: Oil and gas sector
Figure 19: North Sea oil and gas fields
Source: UK Offshore Operators Association, 2002
133

62 Chapter 7: Oil and gas sector
gases was started by BP between its own sectors
and installations in 1999, going company wide in
2000.
137
Internal trading allows companies to
institutionalise the concept of a cost associated
with environmentally damaging emissions,
reinforce a culture of environmental
accountability and develop trading skills to
prepare for the emerging international
marketplace. As a business practice it also allows
a company to allocate capital to initiatives which
have the greatest impact at lowest cost.
138
7.5Recommendations
Pipeline leakage
Although leakage rates have reduced over the last
ten years, methane emissions from gas pipelines
are still significant and becoming more so with
the growth in gas consumption. One of the major
obstacles to achieving reductions in this area is
the poor quality of data. Historically, pipeline
leakage has been primarily a safety issue but with
growing awareness about the environmental
impact of methane emissions, quantification has
become more important. Without a reliable
baseline, there is uncertainty regarding the extent
of the problem and no standard against which to
evaluate any measures taken to mitigate
emissions. Therefore, one of the first steps needs
to be improved monitoring and data collection.
Regular, cost effective programmes for
detecting, prioritising, and repairing leaks across
all sectors of the gas industry – production,
processing, transmission and distribution – are
required. Monitoring equipment could be
installed as part of the ongoing maintenance and
upgrade of the gas pipeline network with a
particular focus on boosters, since this is where
the majority of leaks occur. This would enable
more effective detection as well as more accurate
quantification of gas leaks.
Although leakage represents a loss in revenue
to the industry, the relatively low cost of gas
means the economic incentive to achieve
emissions reductions is weak. Safety tends to be
the main concern at present. Minimisation of
pipeline leakage is therefore more likely to be
underpinned by environmental concerns and
implemented through policy instruments rather
than on an economic basis.
The industry would benefit from a focus on
cost effective technologies and practices that
improve operational efficiency and reduce
emissions of methane. The USA’s Natural Gas
STAR Programme encourages the natural gas
industry to reduce emissions through market-
based activities that are both profitable for
industry partners and beneficial to the
environment.
139
This has introduced a range of
best management practices to achieve emissions
reductions at all stages of the gas production-
distribution cycle. Opportunities and options to
reduce leaks and venting from the largest sources
were jointly identified by EPA and gas industry
representatives and it is intended to reproduce
these solutions across all sectors.
Trading could prove a strong driver towards
Carbon trading has
encouraged the capture of
methane emissions from
oil and gas rigs

63 Chapter 7: Oil and gas sector
lower methane emissions provided additionality
of the savings can be shown. Those reductions
already required through legislation under the
Health and Safety Executive would not qualify as
additional and therefore could not be traded.
Also, the lack of reliable data means there is a risk
of introducing ‘hot air’ into the trading scheme
where the gas industry could be rewarded for
apparent reductions due to statistical error rather
than ‘real’ savings. However, it is debatable as to
whether the industry should be rewarded for
carrying out repairs that should be done as a
matter of course. It is Ofgem’s responsibility to
ensure the necessary investment in pipeline
infrastructure is made and maintained in the long
term. Direct legislation through, for example,
mandatory standards for leakage, is required to
secure further emissions reductions. Improved
data would also help in monitoring and enforcing
such targets.
Venting from rigs
Emissions trading has proved effective in
encouraging methane capture from rigs.
However, with the cessation of the UK ETS in
2006, the opportunity for trading methane will be
lost, at least for two years until the EU ETS review.
This results in a dilemma for the UK Government:
to either legislate to encourage methane capture
and underpin the savings already made or wait
for two years until trading can recommence. Any
legislation must ensure that methane reductions
can still be classed as additional so as not to
undermine the market for trading in the future.

64 Chapter 8: Coal mine methane
8.1 Production
Coal mine methane (CMM) is the term given to
the gas trapped in coal seams, which has an
approximate chemical composition of 70%
methane, 15% carbon dioxide and 15% nitrogen.
The gas is released once the seams are mined and
can then escape to the atmosphere.
Internationally, the UK was the sixth largest
producer of coal mine methane in 1990,
140
behind
China, the former Soviet Union, the USA, Germany
and South Africa. The UK submission to the
UNFCCC declares that 0.24 Mt of methane were
emitted from active coal mines during 2002,
accounting for 12% of all UK methane emissions.
Historically, the contribution of coal mine
methane to the UK’s methane budget was more
significant when major coal fields in the UK
where extensively mined for power generation
and industry (Figure 20). However, the decline of
the UK coal industry and subsequent large scale
pit closures has resulted in far fewer mines and
emissions. In 1947 there were 958 mines
producing 189.6 Mt of coal annually. At present,
there are just 17 deep mines and 39 open cast
mines in the country, producing a total of 27.8 Mt
coal in 2003.
105
The open cast mines release
methane directly to the atmosphere. However,
emissions from such mines are small as the
seams lie close to the surface and have retained
little of their original methane over geological
time.
75
Why recover coal mine methane?
The primary reason for recovering coal mine
methane is safety. Historically, underground mine
explosions have been the cause of many injuries
and fatalities, so reducing methane
concentrations underground has aided mine
safety operations.
Secondly, there is an economic motivation: if
methane from coal mines can be captured, it can
be used directly as a fuel or to generate electricity.
Lastly, there is the environmental imperative:
reducing emissions of methane to the
atmosphere aids the meeting of Kyoto and other
targets.
Abandoned mines
In 1988, a house in the village of Arkwright in
Derbyshire exploded due to contamination of the
village with seeping coal mine methane. Because
the ground above mined seams subsides and
fissures slightly, methane can seep through the
bedrock and find its way to the surface, often
miles from the pit head. This incident was a key
factor in alerting the industry and Government to
Coal mine methane
Figure 20: Coal fields in the UK
Source: Bibler, 1998
140

the environmental impacts of methane emissions
from abandoned mines.
A major shortcoming of the UK UNFCCC
submission is that it only includes emissions from
active mines. At present, the decrease in methane
emissions accounts for 30% of the UK greenhouse
gas emissions reductions achieved since 1990,
with coal mine closure responsible for 36% of this
(i.e. 12% of total greenhouse gas emissions
reductions). Inclusion of methane emissions from
abandoned mines may significantly alter these
figures. Both the current figures and the 1990
baseline would be higher and, whilst emissions
from the sector would still decline over this
period, it would not be so pronounced as
currently implied.
A suitable methodology has not yet been
developed for the inclusion of abandoned mines.
This is a worldwide problem, but particularly
pertinent in the UK. Whilst it is true that
emissions from active coal mines are higher than
from disused mines because the mining process
opens up pockets of methane, abandoned coal
mines are still capable of producing significant
quantities of methane. This is especially true in
the UK where 1096 coal mines have been
abandoned since 1947,
141
compared to the 17 deep
mines still currently active.
Emissions of methane from abandoned coal
mines are poorly quantified at present, with
estimates ranging from 0.02 to 0.3 Mt per year.
64
The large range of values is an indicator of the
massive uncertainty in these estimations. At the
low end of this range, inclusion of abandoned
coal mine methane makes a negligible
contribution to UK methane emissions. The
upper end of this estimate corresponds to more
than doubling the methane released from coal
mines and would make coal mines (active and
abandoned) the second largest source of methane
in the UK, responsible for 21% of UK methane
emissions. The Association of Coal Mine Methane
Operators (ACMMO) believes emissions from
abandoned mines to be higher still, at 0.6 Mt per
year, by including seepage from unvented mines
as well as those with vents.
142
They estimate that
45 sites in the UK are commercially viable, capable
of supporting 300 MW of electricity generating
capacity and saving 0.37 Mt of methane.
142
However, the DTI maintain that coal mine
methane from abandoned mines is not a problem
in the UK and use this assumption as the basis for
their policy recommendations. They estimate
that just 0.05 Mt of methane are emitted from
sites capable of being controlled.
143
Furthermore
they assert that methane seepage from mines
will rapidly diminish, particularly if flooding
occurs.
The Association of Coal Mine Methane
Operators claim that the DTI have seriously
underestimated both the extent of the resource,
the number of possible projects and
overestimated the rate in decline of emissions.
144
The huge discrepancy in both the postulated
resource and its longevity requires further
independent research. At present, poor
knowledge is likely to lead to inappropriate policy
and economic support measures – particularly if
the problem is not perceived as serious.
8.2 Mitigation
Non-extraction
The flow of methane from abandoned coal mines
may be inhibited by blocking vents and sealing
pathways where methane is detected.
Alternatively, the coal mine may be flooded,
providing an aqueous barrier to methane
emissions.
143
Transport of methane through the
water layer is prevented by its low solubility.
Flooding can be an attractive option where there
is no risk of aquifer contamination and where
there is a suitable water resource available for the
operation.
Such techniques are only applicable to sites
where the risk of uncontrolled emissions is low.
Because methane can seep along fissures and
cracks in de-stressed bedrock many miles from its
source, this is not seen as a workable option for
most sites. Indeed, the Coal Authority has had to
65 Chapter 8: Coal mine methane

66 Chapter 8: Coal mine methane
install a further 40 vents at abandoned mines
around the country since 1994 to cope with the
hazards of new leakage points.
143
The preferred options of methane emission
mitigation revolve around recovery and
conversion to carbon dioxide.
Extraction
Coal mine methane can be extracted from mines
in four different ways: through an existing gas
vent,a vent well, a gob gas well and a CBM well.
Existing gas vent
All active coal mines have an existing gas vent to
remove methane from the mine for safety
reasons. Typically this gas is merely vented to the
atmosphere, although some UK collieries do
utilise the methane liberated. In active mines,
ventilation air methane (VAM) is the major source
of methane because the throughput of
ventilation air is so high. Once the mine is no
longer active, the VAM can still be drawn through
the vent and captured, rather than being lost to
the atmosphere (Figure 21).
Vent well
The upper layers of rock above a coal mine can
often subside and fissure, creating a pathway for
methane to seep through to the surface. This
diffuse flow is difficult to capture and can result
in significant methane emissions. A vent well can
be drilled into the disused mine away from the
central shaft and, by pumping on the well,
methane will preferentially exit by this simpler
route. Methane captured here also reduces
methane emissions to the atmosphere.
Gob gas well
Gas trapped in destressed coal seams near the
coal face (known as gob gas) will release methane
into the mine or out through porous rock strata to
the atmosphere. Drilling into this seam and
pumping allows the gob gas to be captured. For
abandoned mines this clearly reduces methane
emissions, whereas for active mines, such a
process mines the gas before the coal is extracted.
CBM well
Vents can also be drilled directly down into coal
seams adjacent to the coal face. Virgin coal
seams are stimulated and, after removing any
water, methane can be extracted from the coal
seam. This is essentially a direct mining process
involving the creation of a virgin coal bed
methane (CBM) mine. As such it is not mitigating
against methane emissions as the methane
present in the coal bed would not naturally have
Methane emissions from
abandoned coal mines are
not recognised by national
inventories

67 Chapter 8: Coal mine methane
escaped to the atmosphere. CBM is a fossil fuel
resource and therefore is not be eligible for ROCs.
Acceleration of coal mine methane
Pumping coal mine methane results in a more
rapid removal of methane from the mine than
would occur naturally and possibly increases the
amount of methane extracted. This lowers the
pressure inside the mine and increases the
desorption of methane from the coal seams.
However, there is still much debate within the
scientific community about the extent of
acceleration.
33
The extent of acceleration has implications for
the trading of methane – does it matter that
methane is being extracted from the mine faster
than baseline natural emissions? Currently, it is
believed that either accepting all extracted
methane by ignoring the acceleration issue or
allocating a fraction of output to be eligible
would both be feasible methods for emissions
trading.
33
Using captured methane
Once captured, coal mine methane is either
vented to the atmosphere, flared (oxidising the
methane to carbon dioxide) or utilised in some
form of energy recovery. The latter is the
preferred environmental option but not
necessarily the most economic since, as a non-
renewable resource, the electricity does not
qualify for ROCs. In 2003, 0.8 TWh of electricity
was generated from colliery methane.
105
Methane is currently captured at seven operating
sites and utilises a mixture of flares, generators
and gas utilisation for boilers. Electricity is
generated at six of these sites. Electricity
generation from CMM also takes place at seven
abandoned mines,
146
with a total capacity of
35 MW. ACMMO estimates that around 300
disused coal mines have the potential to generate
electricity from CMM, which would result in an
installed capacity of around 400 MW.
147
The purity of the methane extracted varies
depending on its source. Gob gas is of medium
quality, typically containing 30-90% methane,
which is a sufficiently high concentration to
utilise abatement technologies similar to those
employed in landfill.
Ventilation air methane and vent well
methane are of lower purity (less than 1%
methane), but more sophisticated technologies
now exist that are capable of utilising this gas
directly.
148
Flow reversal reactors use a bed of
silica gravel or ceramic as a heat exchange
medium. The bed is preheated to 1000ºC to
initiate methane oxidation and the VAM is passed
into the bed. As the methane combusts, the
temperature rises and the excess heat can be
recovered from the exhaust gas. This process also
causes the far side of the bed to heat up, so the
direction is reversed periodically to ensure that
the combustion hotspot remains in the centre of
the reactor bed (Figure 22).
Figure 21: Recovery of methane from abandoned mines
Source: The Coal Authority, 2001
145
Figure 22: Thermal flow reversal reactor
Source: US EPA Coalbed Methane Outreach Program, 2003
149

68 Chapter 8: Coal mine methane
Ventilation air methane may also be utilised as
combustion air – in other words it is used as a
‘primed’ air mix for the combustion of other fuels.
In this way, the calorific value of the VAM is not
lost. Such a process requires an alternate source
of fuel on site.
8.3 Current policy
Coal mine methane emissions
The UK’s current policy on coal mine methane has
recently been laid out by the DTI.
33, 143
The DTI
assessed a total of 18 different policy instruments
on the basis of cost effectiveness, ease of
implementation and political acceptability.
Environmental best-practice was not considered
as one of the criteria. The most important factor
in deciding which policy to utilise was the
assumption that the methane resource from
abandoned mines is small and will reduce over
time through natural processes. However, as
noted earlier, this is a highly contentious
statement.
The favoured policy instrument was a series of
competitive bidding rounds amongst Production
Exploration and Development Licence (PEDL)
holders across relevant sites for the most cost-
effective bids to control methane emissions. The
UK Coal Authority will be responsible for
overseeing this process, thereby extending its
environmental duties from mine water alone to
include greenhouse gases. In most cases, given
the lack of financial support for electricity
generation, it is likely that simple flaring will be
the most cost-effective choice. This policy will
work alongside existing mechanisms, including
the Climate Change Levy (CCL) and emissions
trading.
Of the other policies considered, neither of the
other two ‘front-runners’ – do nothing or
incorporation into the Renewables Obligation –
were deemed acceptable or consistent with
current Government policy. Whilst ‘do nothing’ is
the lowest cost option, it is inconsistent with
Government environmental objectives and runs
contrary to the commitments made on coal mine
methane within the Energy White Paper.
8
Incorporation into the Renewables Obligation was
rejected on the grounds that coal mine methane
is not a renewable resource and that it would
infringe EU rules on state aid. Development of an
‘Alternative Obligation’ for encouraging non-
renewable, yet beneficial, low-carbon
technologies was rejected for fear of raising the
‘nuclear question’.
Whilst the proposal for a competitive grant
scheme is still at an early stage, it is clear that the
emphasis is on control options, rather than
electricity generation. Many proposed methane
mining schemes are to be scrapped due to
insufficient Government incentives.
150
Alkane, a
major CMM company, has dropped proposals for
50 MW of electricity generating capacity in
Ayrshire and is likely to take its operations abroad
to Germany where economic conditions are more
favourable.
Climate Change Levy
Since April 2002, electricity generated from coal
mine plants has been exempt from the Climate
Change Levy (CCL).
151
This full exemption was
incorporated in the 2002 Finance Act, which
accorded CMM renewable status for the purposes
of exempting it from the CCL.
152
The Government
claims that the exemption was granted on the
basis that electricity generated from CMM offers
both environmental gains and employment
opportunities.
151
This creates a policy
inconsistency where coal mine methane is eligible
for Levy Exemption Certificates (LECs) but not
ROCs.
Exemption from the CCL was expected to
boost electricity generation from CMM with a
consequent reduction in GHG emissions.
However, the price of LECs is low at approximately
£4/MWh; an order of magnitude smaller than
ROCs. As a stand-alone policy, the Climate
Change Levy will not provide a sufficient
economic driver for investment in electricity
generation technologies.

69 Chapter 8: Coal mine methane
Emissions trading
In order for the industry to continue to reduce
emissions throughout the UK, the Government
has offered support through other policies such
as the UK Emissions Trading Scheme (UK ETS).
Under the UK ETS, coal mine methane has been
incorporated and rewarded for its environmental
benefits through trading by UK Coal. However,
trading is only allowed for emissions credits
generated from active mines (either through
flaring or electricity generation). Emissions from
abandoned mines do not qualify for carbon
credits since there is no baseline measure for
these emissions and therefore no way for
reductions to count.
DEFRA has commissioned studies to determine
a baseline for abandoned CMM emissions that
could enable it to qualify for this scheme,
64, 141
although so far only a protocol for methane from
working coal mines has been developed.
153
8.4 Recommendations
The key factor in determining the importance of
this sector lies in the debate around abandoned
coal mines, which could shift the current policy
focus. In terms of capturing CMM from both
active and abandoned mines, the technology is
available and ultimately it depends on the policy
emphasis as to how the captured gas is then
dealt with.
Abandoned coal mines
At present, only methane from active mines is
recognised by international targets. As a
consequence, emissions from abandoned mines
are not given the same policy priority as methane
emissions that actively help the UK achieve these
targets. It could be that emissions from
abandoned mines represent both a significant
problem and resource in the UK, but there is a
great deal of uncertainty surrounding current
estimates. Not only does this represent a major
environmental issue, in terms of possible
methane emissions which are currently
unchecked, it is also a potential missed
Capture of coal mine
methane results in both
safety and environmental
benefits

70 Chapter 8: Coal mine methane
opportunity – an unexploited resource which
could provide both financial and environmental
benefits as well as employment opportunities.
An essential first step in addressing this issue
would be to quantify these emissions accurately.
This would involve developing an internationally
agreed methodology for estimating emissions
from abandoned mines, which currently does not
exist. These emissions could then be included in
the UK inventory for the UNFCCC. This would
affect both current and historic estimates of
emissions and therefore the contribution towards
the Kyoto target. Improved data quality would
provide a firmer foundation on which to build
policy and may require a change in policy
direction. The development of a reliable baseline
for abandoned mines would also be required to
enable trading of these emissions. Until
estimates are improved, the debate and
conjecture will persist and methane will continue
to be released into the atmosphere.
Policy
Methane capture
Current policy addresses capture at active sites
but not from abandoned mines. Until emissions
from abandoned mines are better quantified,
there is unlikely to be any change in this
situation.
Electricity generation
Following the recent DTI review, the emphasis in
current policy is on control, most likely in the form
of flaring, rather than energy recovery. Whilst this
is successful in reducing methane emissions and
usually the most cost-effective option, it does not
maximise the environmental benefits of
capturing the gas. Because methane from both
active and abandoned mines is a non-renewable
resource, the economic incentives are not in place
to encourage the implementation of best-practice
technologies. Apart from the Climate Change
Levy, there are no other policies or incentives for
Over 27 Mt of coal was
produced in the UK in
2003

71 Chapter 8: Coal mine methane
energy recovery and the Levy Exemption
Certificates do not have a high enough market
value to encourage energy generation. Fiscal
policies such as trading will encourage flaring
rather than electricity generation, as the most
cost-effective option. Other policies such as feed-
in-tariffs (as in Germany) and incorporation into
the Renewables Obligation have been rejected by
the DTI as inconsistent with existing Government
policy.
Given the lack of financial incentives, if
electricity generation is to be encouraged it will
require some support from the Government. This
could be in the form of grants or subsidies to
encourage the implementation of best-practice
technology, or through legislation, similar to the
EU Landfill Directive. This could have implications
for trading since emissions reductions required or
supported in this way may not then be eligible to
trade.
New technology
There is still room for improvement in current
methane capturing technology, but investment in
increasing efficiency is likely to require some form
of incentive. Similar to energy recovery
technologies, if there are no strong financial
incentives to encourage improved capture,
support may be need through grants and
subsidies or legislation.
Methane trading
The successful trading of methane from active
coal mines on the UK Emissions Trading Scheme
demonstrates the feasibility of this approach for
this sector. Inclusion of emissions from
abandoned mines could potentially double the
size of this market, but first requires the
establishment of a reliable baseline. The two year
gap between the closing of UK ETS and entry of
methane into the EU ETS provides a timely
opportunity to establish this baseline and
investigate the potential of this market. As in the
oil and gas sector, with this gap in trading, the UK
Government faces a choice between legislating to
underpin the savings made to date or putting the
process on hold for two years until trading can
recommence. Similarly, any mandatory
requirements will impact on the viability of the
future trading market.
The current political situation in the UK means
that whilst trading will aid the economics of
installing capturing capacity it will only
encourage capture and flaring rather than
electricity generation. Other policy measures
need to be put in place to promote the adoption
of energy recovery, which could then be
supported through trading.

72 Chapter 9: Discussion and conclusions
9.1 Importance of methane
Methane is a powerful greenhouse gas, twenty-
three times more potent than carbon dioxide
(over a 100 year lifetime) and with a relatively
short atmospheric lifetime of just 12 years,
meaning that emissions reductions are rapidly
translated into atmospheric concentration
reductions. Therefore mitigating methane is
highly cost-effective, particularly in the short
term. Despite this, there is currently a lack of
policy specifically targeted at methane.
There is also a climate change imperative for
reductions in methane emissions to be achieved
sooner rather than later – the higher the
concentration of methane in the atmosphere, the
more slowly it is removed by natural processes
due to feedback loops in the atmospheric
chemistry of the gas. Therefore it is more
effective to reduce emissions in the short term;
failure to do so will increase the lifetime of
methane in the atmosphere and make it an even
more potent greenhouse gas.
Controlled properly, methane represents a
valuable resource – it is a combustible fuel with a
high calorific value. Once captured, combustion
of methane produces the less potent carbon
dioxide and energy, which can then be used for
heating or electricity generation. Production of
electricity from methane will offset electricity
production from the more polluting national
energy mix.
Hence, the chemistry and physical properties
of methane make it an attractive option for
emissions reductions within the framework of the
basket of six greenhouse gases, providing both
environmental and economic benefits. The
question is how best to secure these reductions –
what policies and technologies would be most
effective?
9.2 Disparity of methane sources
This report has focused on the four major sources
of methane in the UK: landfill, agriculture, gas
pipes and coal mines. These are disparate in
nature, differing in the way in which the methane
is generated, control options available and the
overall policy context.
Sources may be either biogenic (agriculture,
landfill) or fossil fuel derived (gas leakage and
coal mines). This has implications for how
methane is classified (renewable or non-
renewable) and therefore its eligibility for
financial rewards such as ROCs. Furthermore, the
source may be a single point and therefore
inherently capturable (landfill, coal mines) or
essentially diffuse (agriculture, gas leakage). To a
certain extent, this determines whether the policy
emphasis is on capture or reduction and whether
the resource can be further exploited.
Each sector also has its own political history,
with different players and sensitivities, and
particular policy focus. All these factors together
make identifying a single unifying methane policy
a major challenge.
9.3 Methane trading
Although there are policies in place that will have
the effect of reducing methane, these are not
uniform across the four major sectors and are
often focused on a different goal (e.g. diverting
waste from landfill). Methane trading was a key
option considered in this report as a possible
means of unifying policy into a single coherent
abatement mechanism. According to the main
criteria necessary for an effective emissions
trading scheme (Chapter 3), there are a number of
drawbacks to implementing a UK methane
trading scheme:
• Commodity to trade. This requires
quantification of the methane available for
trading which is most easily achieved through
capture, but this is only possible in certain
sectors.
• A liquid market. The methane market alone is
too small to function efficiently since the
volumes involved are too low. For methane to
be traded it must be incorporated into a multi-
gas trading scheme.
Discussion and conclusions

• Suitable mix of players. There is a wide
variation in the size of players across the
different sectors, from big oil companies to
individual farmers, with a large number of
small players, which would result in an
inefficient market.
• Additionality. Mandatory requirements for
methane reductions are already in place in
several sectors so future reductions could not
be considered additional and are therefore not
tradable.
• Monitoring, reporting and verification. In the
sectors where methane is capturable (landfill
and coal mines) data quality is poor with no
reliable baseline to provide certainty and allow
for verification.
• Conflicting policies. Where methane is captured
and used to generate electricity, it is financially
advantageous to accrue alternative
environmental rewards such as ROCs due to
their high market value, rather than carbon
credits. Since the savings cannot be counted
twice, this undermines any potential trading
market.
It is apparent that a separate methane market
does not represent a viable option for the UK, nor
would methane trading work as the sole
approach to cover all sectors. However, trading
methane certainly has potential for some sectors,
as demonstrated by the successful trading in the
UK Emissions Trading Scheme (UK ETS) by the coal
and gas industry.
The possibilities for trading vary between
sectors, as detailed below and summarised in
Table 16.
• Landfill. Methane is capturable, but does not
count as additional since capture is already
required for safety reasons and also covered at
new sites by the Landfill Directive. A reliable
baseline is difficult to define, partly due to the
lack of data on landfill sites and partly due to
the change in levels of methane emissions that
occurs naturally over time. Any electricity
generated from the captured methane will be
eligible for ROCs, removing the incentive to
trade.
• Agriculture – livestock. Livestock emissions are
diffuse, with no easy means of capture and no
accurate method for estimating a baseline. As
small players, individual farmers would find it
hard to compete effectively in a trading scheme
– some form of aggregation would be necessary
but this would introduce further complexity.
• Agriculture – manure. With appropriate
management, emissions from manure are
capturable, although there is little data
currently available to determine a baseline of
emissions. The methane captured would be
additional since there are no other policies in
this area, but the availability of ROCs may
undermine the potential for trading.
73 Chapter 9: Discussion and conclusions
Table 16: Potential for methane trading in each sector
Is methane
capturable & Reliable Is methane Policy
quantifiable? baseline? additional? conflict? Trading?
Landfill Yes No No ROCs No
Agriculture
– livestock No No Yes No No
–manure Yes No Yes ROCs Possible
Oil & gas rigs Yes Yes Yes No Yes
Gas pipeline No No Some No Possible
Coal mines Yes No Yes No Yes

74 Chapter 9: Discussion and conclusions
• Oil & gas rigs. Methane is capturable, additional
and quantifiable with no policy conflicts,
resulting in a high trading potential.
• Gas pipelines. In a sense, emissions from
pipeline leaks are (re)captured by repairing the
leak, since the methane is already captured
within the pipe, but these emissions reductions
are not easily quantified. For trading to be
possible, a reliable baseline, through improved
monitoring, needs to be established to enable
quantification. Only those emissions not
covered by Health and Safety legislation would
count as additional.
• Coal mines. Trading potential for this sector is
high, capture of emissions being reasonably
straightforward and additional, with no policy
conflicts. Methane from active mines has been
successfully traded. However, there is huge
uncertainty regarding emissions from
abandoned mines, which could double the
market size. Better quantification is required
before any trading of these emissions can
commence.
Given the forthcoming closure of the UK ETS in
2006, the future of methane trading is somewhat
uncertain, awaiting the review of the EU ETS in
2006. It is essential that methane is incorporated
into the European scheme in 2008, given its
importance as a greenhouse gas. Even limited
trading should be encouraged because of the
potency of the gas. In addition, some
consideration needs be given to the two year gap
following the end of the UK ETS in 2006. The UK
Government is faced with a choice of putting the
process of methane reductions from trading on
hold for this period or underpinning the savings
achieved to date through legislation. Any policies
must ensure that the methane reductions can
still be classed as additional to allow trading of
these emissions in the future.
Although the opportunities for methane
trading in the UK are limited, mainly due to the
presence of ROCs, there may be greater scope for
trading in other countries. Under the EU ETS, the
Joint Implementation and Clean Development
Mechanism of the Kyoto Protocol open up the
possibility of trading reductions secured through
projects in other countries, which could help
boost the market in the UK.
Despite the fact that methane trading does
not represent the ultimate solution in terms of
single coherent approach for reducing methane
emissions, it still has a role to play as part of a
synergistic policy package. However, the future of
the market is dependent on inclusion in the EU
ETS. Until this is certain, the potential of this
policy option will be left hanging.
9.4 Recommendations
Based on the likely future emissions from each
sector and the effect of planned policies and
measures, annual methane emissions are
expected to decrease by 16.5% by 2020.
136
However, additional policy measures have the
potential to reduce this yet further, with a suite of
policies to address the different requirements in
each sector; these are illustrated in Table 17 and
discussed on a sector by sector basis below.
Landfill
Reductions in methane emissions from landfill
sites can be achieved by two routes: capturing
any methane produced as a result of anaerobic
decomposition of biodegradable waste and
reducing the amount of biodegradable waste sent
to landfill in the first place, as laid out in the EU
Landfill Directive.
One of the key issues for this sector is data
quality. There is uncertainty about the exact
number of landfill sites in the UK and extent of
capture at many of these sites, particularly older
and closed sites. It could be that a significant
source of methane emissions is being overlooked.
A detailed inventory of all landfill sites is
essential, providing information on the capture
technologies employed at each site to give an
indication of where further reductions could be
made.
Methane trading is
unlikely to be an option
for reducing livestock
emissions

75 Chapter 9: Discussion and conclusions
In modern landfills, 85% of the methane can be
captured
25
although the capture rate could be
increased still further. Older landfill sites with
less advanced capping technology have lower
rates of capture. If such sites are found to be a
significant source of emissions, investment will be
needed to find solutions to improve capture at
these sites. The prime economic policy
instrument for improved methane capture at
present is eligibility for ROCs through the
generation of electricity from landfill gas.
The success, or otherwise, of the Landfill
Directive will depend on effective alternative
methods for the disposal of biodegradable waste.
Whilst there is no lack of such options –
composting, recycling, incineration – the main
obstacle appears to be their implementation. An
increase in composting or recycling requires
individuals to change their waste disposal habits
and, although composting and recycling rates
have increased, it is unclear whether these are
capable of increasing to the levels required by the
Directive. Incineration is also unpopular amongst
the UK public, with health concerns about dioxins
and other emissions from waste incineration
plants. Furthermore, electricity generation from
incineration of waste does not qualify for ROCs.
Anaerobic digesters offer the best alternative
at present, particularly as part of a mechanical
biological separation scheme, with close to 100%
methane capture and no atmospheric emissions.
The gate fees for accepting the waste are a key
economic driver for this technology. In addition,
electricity generated from the methane is eligible
for the strong financial rewards of ROCs.
However, in order to encourage the initial uptake
of this technology, it may be necessary to provide
additional support in the form of grants and
subsidies, since it is a relatively unproven
technology in the UK.
The effectiveness of the Landfill Directive in
achieving significant reductions in landfill
methane emissions remains to be seen. There is
some incompatibility with the UK Renewables
Obligation, since a reduction in biodegradable
waste going to landfill will reduce the
profitability of methane capture and could
theoretically make capture and use unviable.
However, substantial amounts of methane will be
produced from the biodegradable waste already
present in landfill for many years to come,
minimising any potential conflict.
Agriculture
The agricultural sector is the largest source of
methane within the UK, but the hardest one in
which to achieve emissions reductions, reflected
in the lack of polices that target this source.
Table 17: Disparity of methane sources and appropriate mitigation measures
Collectable Non-collectable Possible measures
Landfill
Agricultural manure
management
Biogenic Divert from landfill
Societal trends
Agriculture
livestock
Coal mine methaneFossil fuel Carbon trading
Direct policy measures
Gas pipe leakage
Flare
Revenue streams:
– use as heating fuel
– generate electricity
– ROCs or carbon trading
Possible measures Reduce at source
Carbon trading
(if quantifiable)
Direct policy measures

76 Chapter 9: Discussion and conclusions
Livestock emissions
Some 90% of emissions are from ruminant
mammals such as cows and sheep. These sources
of methane are a multitude of mobile point
sources rendering capture of the methane
unfeasible. Reduction of methane at source is
therefore the only sensible mitigation measure.
However, the policy options available to achieve
this are fraught with difficulty. Enforcing a
reduction in livestock numbers would alienate the
farming community whereas increasing
productivity or reducing emissions per animal
through dietary adjustments or genetic
engineering is likely to be unpopular amongst the
public.
Some decrease in the number of animals may
occur as a result of reforms to the EU Common
Agricultural Policy (CAP). The current societal
trends towards organic produce and
vegetarianism may also help reduce livestock
numbers, but not by any significant amounts and
this is also an area that would be difficult to
legislate. Supporting moves towards more
sustainable methods of farming could be of
benefit over the longer term by reducing livestock
densities.
It seems that it may be necessary to accept a
certain level of methane emissions from
agriculture if the UK is to retain a livestock
farming industry.
Manure management
Options for reducing methane emissions from
animal manure are more straightforward, the
most favourable being the use of anaerobic
digesters. A strong economic driver is already
available through eligibility for ROCs. The main
focus here needs to be on raising awareness
about this technology amongst the farming
community and encouraging its uptake through
grants and subsidies and the formation of
farming co-operatives with shared digester
facilities.
Oil and gas industry
Natural gas leakage
Once again, poor data quality is a key issue for
this sector. At present, estimates of methane
emissions from pipeline leaks are very poorly
quantified, with errors of ±40%. This represents
one of the main barriers to trading at present,
with a risk of trading apparent reductions due to
statistical error rather than ‘real’ savings.
Improved monitoring and data collection are
required to establish the extent of this problem.
Due to the relatively low price of gas, there is
little economic incentive to repair leaks and
reduce emissions. Programmes such as the USA’s
Natural Gas STAR programme help to reduce
emissions through market-based activities that
benefit both the industry and the environment.
However, stronger measures are needed to
achieve significant reductions, with Ofgem
overseeing tighter regulation on pipeline leakage
and the setting of mandatory standards. Any
such legislation would remove the possibility of
trading from this sector, but it is questionable as
to whether the industry should be rewarded for
carrying out necessary repairs anyway.
Venting from rigs
Reducing methane emitted as a result of rig
flushing is straightforward through flaring or
Strong regulation is
required to reduce leakage
from gas pipes

77 Chapter 9: Discussion and conclusions
sequestration of the captured methane. The
primary economic incentive for achieving these
reductions to date has been through the trading
of methane on the UK ETS. This raises the
question of what will happen once the UK ETS is
closed. Clearly, it is not desirable to have
technologies ready to be implemented in the UK,
yet no policy or financial drivers to encourage this
until methane can be traded on the EU ETS in
2008. An interim policy measure is required to
reward any greenhouse gas emission abatement
that occurs in the period to 2008. However, if
trading of these emissions is to continue in the
future, any measures must ensure that the
methane reductions can still be classed as
additional.
Coal mine methane
A major issue for this sector is emissions from
abandoned mines. Estimates of these emissions
vary by a factor of 10 and so could represent a
significant, but unrecognised, source of methane
emitting to the atmosphere. Reliable inventory
information and international agreement on how
to classify methane from abandoned coal mines
are a priority to put this source into perspective
and assist in future policy decisions on its status.
Once a source is identified, coal mine methane
is straightforward to capture and therefore easily
quantified, making it an ideal candidate for
trading, as demonstrated by successful trading in
the UK ETS. Methane from both active and
abandoned mines should be traded. The value of
carbon credits should provide a sufficient driver
for investment in the capital equipment required
to capture the coal mine methane. Without ROCs,
there is currently little incentive to use the
captured methane to generate electricity since
flaring is the cheapest option and all that is
required for trading (the trading value
determined by offsetting the methane saved
against the carbon dioxide produced). Flaring is
also the method favoured by present policy, which
focuses on the most cost-effective control of
emissions from active mines. Environmentally,
energy recovery is the preferred choice, but this
requires more active support from the
Government.
As with emissions from oil and gas rigs, once
the UK ETS has closed, it is recommended that
interim support policies are introduced to support
emissions reductions until methane trading is
incorporated into the EU ETS. Once again, these
measures must ensure that any methane
reductions can still be classed as additional if
trading is to occur in the future.
9.5 Conclusions
Reductions in methane emissions represent a
rapid and cost-effective option for lowering
greenhouse gas emissions. It is essential that
these reductions are realised now, before
atmospheric concentrations of methane rise and
its potency increases.
Although methane trading is at first sight a
highly attractive option for mitigating methane
emissions, in practice most methane generating
sectors are excluded due to other policy
instruments (no additionality), other economic
drivers (more attractive), small players (reduces
liquidity) and poor quantification of emissions
(introduction of hot air). Only coal mine methane
and emissions from oil and gas rigs are currently
viable sectors for exploiting the methane trading
opportunity and this is dependent on
incorporation into the European Emissions
Trading Scheme in 2008.
A synergistic package of polices is required in
each sector to secure the significant potential
reductions and in nearly all cases improved data
collection is necessary. Technological
development and social and economic policy all
have an integrated role to play. Methane
abatement has been overlooked in the past, but it
is a crucial component in mitigating climate
change and should be an early focus of any
strategy to reduce greenhouse gas emissions.

78 Glossary
Abandoned coal mines Mines which are no longer being mined for coal
Abatement A reduction in the amount or intensity of emissions
Active coal mines Mines which are still operative and producing coal, either deep mines or
open cast
Additionality A requirement that emissions reductions associated with a greenhouse
gas mitigation project must exceed those that would have occurred in the
absence of the project
Aerobic In the presence of, or requiring, oxygen
Allowances The right to emit a quantity of a pollutant under an emissions trading
scheme
Anaerobic In the absence of oxygen
Anthropogenic Made by humans or resulting from human activity
Baseline-and-credit system A market-based approach which allocates a pre-determined emissions
profile to each participant and allows trade in the unused portion of that
profile
Bedrock The solid rock that underlies soil and other loose material
Biodegradable Material that can be broken down by micro-organisms into simpler
compounds
Biogas A combustible gas created by the anaerobic decomposition of organic
material, composed primarily of methane, carbon dioxide and hydrogen
sulphide. This can be produced at landfill sites, wastewater treatment
facilities and animal waste treatment facilities
Biogasification The breakdown of complex biological materials by anaerobic bacteria to
more useful forms of fuel: carbon dioxide and methane
Biogenic Produced by the action of living organisms or biological processes
Biomass Plant-based materials that can be burned to produce energy or converted
into a gas and used for fuel
BSE Bovine Spongiform Encephalopathy is a chronic progressive degenerative
disease affecting the central nervous system of adult cattle, also known
as Mad Cow Disease
Calorific value The heat produced by the complete combustion of a given quantity of
fuel under specific conditions, measured in calories. The calorific value of
household waste is about one-third that of coal
Cap-and-trade system A market-based approach where a cap, or maximum limit, is set on
emissions and sources covered by the system receive authorisations to
emit in the form of emissions allowances, with the total amount of
allowances limited by the cap
Capping layer An impermeable layer of clay or artificial membrane near the surface of a
landfill site forming a barrier between the contaminated material and the
atmosphere.The cap is designed to keep water out (to prevent leachate
formation) and also helps to capture landfill gas
Glossary

79 Glossary
Carbon credits An amount of carbon that has been mitigated by a project that can then
be used as a tradable commodity to offset greenhouse gas emissions
Carbon cycle The exchange of carbon in various forms (carbon dioxide, carbonates,
organic compounds etc.) between the atmosphere, ocean, terrestrial
biosphere and geological deposits
CDM The Clean Development Mechanism is a market mechanism defined in
the Kyoto Protocol (Article 12) as a project between a developed country
and a developing country that provides the latter with the financing and
technology for sustainable development, and assists in achieving
compliance with its emission reduction commitments
Clear Skies Programme UK capital grant scheme for promoting renewable energy technologies
including solar thermal, biomass boilers and heat pumps
Climate change A long-term change in temperature, precipitation, wind and all other
aspects of the earth’s climate due to natural or human activity. Climate
change is defined by the United Nations Framework Convention on
Climate Change as “a change of climate which is attributed directly or
indirectly to human activity that alters the composition of the global
atmosphere and which is in addition to natural climate variability
observed over comparable time periods”
Co-firing The use of two or more different fuels (e.g. wood and coal)
simultaneously in the combustion chamber of a power plant
Composting Biological decomposition of organic materials in the presence of oxygen
by bacteria, fungi and other organisms into a soil-like product called
humus
Condensate A light liquid hydrocarbon produced when hydrocarbon vapours are
cooled
Digesta Intestinal contents
Digestate The solid residue produced in an anaerobic digester, similar to compost.
The digestate usually requires stabilisation by composting before a
saleable product can be produced
Dioxins Highly toxic compounds that are a by-product of incineration of plastics.
Also generated by bush fires, volcanoes and vehicle emissions
Direct emissions Greenhouse gas emissions by an entity from sources owned or controlled
by that entity
Energy recovery The process of extracting useful energy from waste, typically electricity or
heat (or both)
Enhanced greenhouse effect The increase in the natural greenhouse effect through increased
concentrations of greenhouse gases as a result of human activities
Enteric fermentation A digestive process of some mammals by which carbohydrates are broken
down by micro-organisms into simple molecules to aid absorption into
the bloodstream

80 Glossary
Eutrophication The process by which water becomes enriched with plant nutrients, most
commonly phosphates and nitrates. This promotes algae growth which,
when it dies, can lead to the depletion of dissolved oxygen, killing fish and
other aquatic organisms. While eutrophication is a natural, slow-aging
process for a body of water, human activities can greatly accelerate the
process
Feed-in tariffs A form of support for electricity generated from renewable sources.
Typically a premium price is paid to generators of green electricity
Financial derivatives A risk-shifting agreement, the value of which is derived from the value of
an underlying asset. The underlying asset could be a physical commodity,
an interest rate, a company’s stock, a stock index, a currency, or virtually
any other tradable instrument upon which two parties can agree
Flange A device to connect a pipe to another pipe, a valve or other piece of
equipment, and maintain a seal
Foot and Mouth disease An acute contagious viral disease of cloven-footed animals (e.g. cattle,
sheep, goats, pigs) marked by ulcers in the mouth and around the hoofs
Fossil fuel Naturally occurring carbon or hydrocarbon fuel (e.g. coal, natural gas and
oil) formed by the decomposition of ancient animal and plant remains
formed over millions of years
Gate fee The fee, usually quoted in £ per tonne, for processing waste at a
treatment and/or disposal facility
Global warming The rise in temperature of the earth’s surface due to the enhanced
greenhouse effect
Global Warming Potential A measure of the relative strengths of different greenhouse gases.
Defined as the cumulative radiative forcing of the gas compared to
carbon dioxide over a specified time horizon (usually 100 years)
Grandfathering A method of centrally allocating emissions allowances, usually based on
historical emissions
Greenhouse effect An increase in the earth’s temperature caused when the atmosphere
transmits incoming solar radiation but blocks outgoing thermal radiation,
primarily due to the presence of carbon dioxide and water vapour in the
atmosphere
Greenhouse gas An atmospheric gas that has the ability to absorb infrared radiation,
contributing to the greenhouse effect (e.g. water vapour, carbon dioxide,
methane)
Heat exchange The transfer of energy between two substances at different temperatures,
providing required heating or cooling
Heavy metals Metallic elements with high atomic weights that can damage living
things at low concentrations and tend to accumulate in the food chain
(e.g. mercury, chromium, cadmium, arsenic, and lead)
Hot air Emissions reductions against a target that occur without any dedicated
abatement actions (e.g. due to economic downturn or prior legislation)

81 Glossary
Hydrolysis Reaction of a chemical compound with water
Hydroxyl radical A highly reactive molecule containing one oxygen and one hydrogen
atom responsible for the removal of many trace pollutants from the
atmosphere
Indirect emissions Emissions that result from the activity of an entity but are produced by a
source external to the entity. For example, emissions occur because
households use electricity, but the source of the emissions is a power
station, not the house
JI Joint Implementation is a mechanism of the Kyoto Protocol where a
developed country can receive carbon credits when it helps to finance
projects that reduce net emissions in another developed country
(including countries with economies in transition)
Leachate A liquid that results from water collecting contaminants as it trickles
through wastes, agricultural pesticides or fertilizers and may result in
hazardous substances entering surface water, groundwater or soil
Lifetime The approximate amount of time a gas is present in the atmosphere
before being removed from the atmosphere by conversion to another
chemical compound or via a sink
Liquid market A market where buying and selling can be accomplished with ease due to
the presence of a large number of interested buyers and sellers prepared
to trade substantial quantities at small price differences
Liquidity The ease with which an asset can be converted to cash
Methanogenesis The production of methane and carbon dioxide by biological processes
carried out by single-celled micro-organisms called methanogens
Methanogenic Methanogenic micro-organisms produce methane and carbon dioxide by
the fermentation of simple organic compounds or the oxidation of
hydrogen under anaerobic conditions
Methanotroph An aerobic bacterium with the ability to utilise methane as sole carbon
and energy source
Mitigation Steps taken to avoid or minimise a negative environmental impact. This
might include minimising, rectifying, reducing or compensating for the
impact
Montreal Protocol An international agreement to limit further damage to the ozone layer by
drastically reducing the production and consumption of ozone-depleting
substances (e.g. chlorofluorocarbons, halons, carbon tetrachloride). The
treaty was signed in 1987 and substantially amended in 1990
Natural Gas STAR Programme A USA voluntary initiative which aims to encourage natural gas
companies to adopt ‘best management practices’ that can profitably
reduce emissions of methane
Perturbation lifetime A measure of the lifetime of a gas that includes its influence on other
atmospheric species that occurs during its physical lifetime.

82 Glossary
Potency (of a greenhouse gas) The capacity of a gas to absorb and radiate heat energy over a specified
period of time
Radiative forcing A change, over time, in the balance between incoming solar radiation and
outgoing infrared radiation, due to natural or anthropogenic causes.
Positive radiative forcing warms the earth’s surface whilst negative
forcing cools
Recycling The series of activities by which waste materials are collected, sorted,
processed and converted into raw materials for use in the manufacture of
new products
Renewable energy Energy obtained from sources which are essentially inexhaustible.
Renewable sources include hydroelectric power, wood (biomass),
geothermal, wind, photovoltaic and some waste
Ruminant An animal that chews its cud, has even-toed hooves and a multi-
chambered stomach (e.g. cattle, sheep, goats, deer)
Ter mite A soft-bodied ant-like insect which feeds on wood
Volatile organic compounds Hydrocarbon based compounds that evaporate rapidly at ambient
temperatures. These chemicals are often used as solvents and many are
hazardous air pollutants such as benzene
Wetlands Areas that are inundated or saturated by surface water or ground water
at a frequency and duration sufficient enough to support vegetation
adapted for life in saturated soil conditions. Wetlands generally include
swamps, marshes, fens, bogs and similar areas

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89 Appendix 1
Tropospheric oxidation
The predominant mechanism for removal of
methane from the earth’s atmosphere is
oxidation within the troposphere by the hydroxyl
(OH) radical. The hydroxyl radical is responsible
for the breakdown and removal of a host of trace
gases, including methane, and for this reason is
known as the ‘cleanser of the atmosphere’. In
essence, atmospheric OH effects a low
temperature combustion of ‘fuels’, such as
methane and other hydrocarbon species, by
oxidising CH
4
to CO
2
, as would happen if methane
were burned.
The chemistry of methane in the troposphere
is very simple as it only reacts with the hydroxyl
radical and no other species. Methane is
moderately chemically inert and even the
reaction with OH is slow compared to other
related hydrocarbons. However, whilst the
reaction of CH
4
and OH is in itself simple, the
network of inter-related chain reactions makes
the bigger picture somewhat more complex. The
removal of CH
4
from the atmosphere is
intrinsically tied up with the chemistry of other
species, notably the hydroxyl radical, carbon
monoxide (CO), ozone (O
3
) and oxides of nitrogen
(NO & NO
2
, termed NO
x
). Carbon monoxide and
the nitrogen oxides are known as ‘indirect’
greenhouse gases because, although they are not
active greenhouse gases in themselves, they
strongly affect the concentrations of the major
greenhouse gases, such as CH
4
,by either
increasing their lifetimes or controlling O
3
and OH
concentrations.
The process of tropospheric oxidation of
methane is complex, with numerous feedback
loops, as shown in Figure 23. Methane reacts with
hydroxyl to form the methyl radical (CH
3
) and
water. The methyl radical undergoes further
reactions to form either methyl hydroperoxide
(CH
3
OOH) or formaldehyde (HCHO). Both these
species are soluble in water vapour and can be
removed from the atmosphere as rain.
Formaldehyde can also decompose in light to
produce carbon monoxide (CO).
The slowest step of the reaction overall, and
therefore the step that governs the speed of the
entire reaction scheme, is the initial reaction
between CH
4
and OH. The rate of removal of
methane from the atmosphere is dependent on
both the concentration of methane in the
atmosphere and the concentration of the
hydroxyl radical. An increase in methane
concentration results in an increased rate of
removal from the atmosphere, assuming OH
concentration remains constant. However,
because of feedbacks in the above reaction
Appendix 1: The atmospheric chemistry of
methane
Figure 23: Oxidation of methane in the
troposphere

90 Appendix 1
scheme and other reactions, the OH concentration
does not remain constant.
The initial reaction between CH
4
and OH
removes one OH radical from the atmosphere for
every CH
4
oxidised. Further steps in the reaction
sequence generate NO
2
, which can create OH
radicals, and CO, which can remove them. Overall,
the influence of CO is the more important and so
the reaction scheme results in a net removal of
OH radicals. An increase in CH
4
concentration will
therefore remove OH from the atmosphere and
thereby slow its own removal. This increases the
atmospheric lifetime and subsequent
environmental impact of CH
4
.With methane
emissions predicted to continue increasing, the
lifetime of CH
4
in the atmosphere and therefore
its Global Warming Potential (GWP) is predicted
to increase over the coming years.
Role of the hydroxyl radical
The lifetime of methane is strongly tied to the
chemistry and abundance of the hydroxyl radical,
OH. Whilst feedback loops in the oxidation of CH
4
affect the concentration of OH in the atmosphere,
the influence of the so-called indirect greenhouse
gases CO and NO
x
is much more pronounced. The
chemistry of these species and their influence on
OH concentrations in the troposphere is a major
factor in the rate of removal of CH
4
from the
atmosphere. Sources and sinks of the hydroxyl
radical are shown in Figure 24.
Ozone is the main precursor of the hydroxyl
radical and is the ultimate source of all oxidising
reactions in the troposphere. Approximately 10%
of ozone in the atmosphere resides in the
troposphere, generated by the action of light on
NO
2
and molecular oxygen (O
2
), or transferred
from the stratosphere. The relative importance of
these two formation pathways is still a matter of
some debate, although it is now generally agreed
that the two sources are approximately equal.
27
Increased anthropogenic NO
x
emissions will
increase tropospheric ozone concentrations and
therefore reduce CH
4
concentrations in the
troposphere, at the expense of air quality.
Depletion of the ozone layer in the stratosphere
will reduce the amount of ozone transferred into
the troposphere but will also allow more light
through, thereby increasing O
3
production in the
troposphere from NO
2
.
Ozone decomposes in light (and in doing so
absorbs harmful uv radiation) and splits into
molecular oxygen and an oxygen atom. The
oxygen atom is electronically excited and hence
highly reactive (denoted by O*). This species can
abstract a hydrogen atom from water yielding
two hydroxyl radicals. It is important to note that
this process requires light and so OH
concentration in the atmosphere shows daily,
seasonal and spatial variations in concentration.
The rate of hydroxyl production is also dependent
on atmospheric water vapour concentration.
As well as the important role OH plays in
initiating oxidation chains that remove methane
from the atmosphere, it similarly removes other
volatile organic compounds (VOCs) and nitrogen
dioxide from the atmosphere. Other trace
Figure 24: Sources and sinks of the hydroxyl
radical

91 Appendix 1
species, such as HO
2
, can also be removed by
reaction with the OH radical. However, the main
reaction that affects the concentration of OH in
the atmosphere is the reaction with carbon
monoxide, CO. This reaction is much more rapid
than the reaction between CH
4
and OH, and CO
concentrations are comparatively high. This
pathway is a significant mechanism for reducing
OH concentrations in the atmosphere and
subsequently reducing the rate of methane
removal from the troposphere. Approximately
50% of CO in the troposphere is derived from
oxidation of methane and other VOCs, so an
increase in methane concentration causes an
increase in CO concentration which will in turn
decrease the rate at which OH removes methane.
These feedback loops are accounted for in the
perturbation lifetime of 12 years for CH
4
.
However, increased anthropogenic production
rates of CO have the potential to throw this
system out of balance.
Stratospheric oxidation
Some of the methane present in the troposphere
passes into the stratosphere. Approximately 40
Mt of CH
4
are oxidised in the stratosphere,
representing around 7% of all CH
4
removal. The
chemistry of methane in the lower stratosphere is
identical to that in the troposphere, with OH
radicals oxidising CH
4
in the same manner.
Indeed, oxidation of methane to CO
2
and water is
the source of approximately 50% of stratospheric
water vapour.
In the upper stratosphere, methane
decomposition can be initiated in two other ways;
by reaction with chlorine radicals or excited
oxygen atoms. Ultraviolet light, which has high
intensities in the stratosphere, causes the
dissociation of a carbon chlorine bond, releasing a
chlorine radical.
CH
3
Cl CH
3
+ Cl
The chlorine radical may then react with
methane forming a methyl radical and hydrogen
chloride.
Cl CH
4
CH
3
+ HCl
Alternatively, uv light also causes the
dissociation of ozone to yield an oxygen molecule
and an electronically excited (highly reactive)
oxygen atom (O*).
O
3
O
3
+ O*
The excited oxygen atom can also initiate the
oxidation of methane, yielding a methyl radical
and a hydroxyl radical.
O* CH
3
+ OH
The reaction of CH
4
with either Cl or O* yields a
methyl radical, which undergoes subsequent
reactions to form CO
2
and H
2
O in the same
manner as in the troposphere (Figure 23). The
only difference between the chemistry of
methane in the upper stratosphere compared to
the troposphere and lower stratosphere lies in the
possibility of different chain initiation steps that
do not rely on the hydroxyl radical.
The main sources of chlorine radicals are
methyl chloride (CH
3
Cl), trichlorofluoromethane
(CFCl
3
), dichlorodifluoromethane (CF
2
Cl
2
), carbon
tetrachloride (CCl
4
) and 1,1,1–trichloroethane
(CH
3
CCl
3
). Of these, only methyl chloride is of
natural origin, the others are all man-made
compounds. These CFCs are responsible for the
thinning of the ozone layer in polar regions and
emissions are now strictly controlled under the
Montreal Protocol. However, these species are
long lived in the atmosphere and will continue to
exist in relatively high concentrations over the
course of the next century.
Uptake by soils
Approximately 30 Mt of CH
4
are removed from
the atmosphere annually through uptake by soils.
Soils contain populations of methanotrophic
bacteria that can oxidise methane. These bacteria
are of two sorts: those that carry out high affinity
oxidation and those that carry out low affinity
oxidation.
‘High affinity oxidation’ is where
Light
Light

92 Appendix 1
methanotrophic bacteria consume methane that
is in low concentrations, close to that of the
atmosphere (<12ppm). It is this process that acts
as an atmospheric sink for CH
4
from the global
atmospheric burden. The bacteria favour upland
soils, in particular forest soils. The bacteria
responsible for high affinity oxidation processes
remain largely unknown. It is known, however,
that high ammonium concentrations in soils lead
to a loss of methanotrophic bacteria and a
subsequent reduction in the rate of methane
oxidation. The use of artificial fertilisers
containing ammonia is therefore detrimental to
the uptake of CH
4
.
‘Low affinity oxidation’ occurs where
methanotrophic bacteria operate under methane
concentrations considerably higher than in the
atmosphere. These bacteria exist in wetlands,
paddy fields and landfill site caps where there are
high methane concentrations due to the presence
of methanogenic bacteria. Low affinity oxidation
does not remove CH
4
from the atmosphere and is
not included in the value of 30 Mt CH
4
taken up
by soils annually. However, because
methanotrophic bacteria working under low
affinity oxidation conditions absorb up to 90% of
the CH
4
produced by methanogenic bacteria in
the same environment, they significantly reduce
CH
4
emissions from these sources. These bacteria
are also highly susceptible to anthropogenic
influences on their habitat, like land and water
management, use of chemical fertilisers and
pesticides and soil acidity. Changes in CH
4
emissions from paddy fields and other wetlands
may be due to changes in the balance between
methanogenic and methanotrophic bacteria in
the environment.
Increases in atmospheric CH
4
concentrations
may inhibit the microbial uptake of CH
4
in soils
via a process that couples soil methane and
ammonia. However, the effect is expected to be
small, since the global sink strength for microbial
uptake of CH
4
by soils is only 30 Mt/yr.

Notes

Notes

Notes

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