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There is growing international interest in mitigating climate change during the early part of this century by reducing emissions of short-lived climate pollutants (SLCPs), in addition to reducing emissions of CO2. The SLCPs include methane (CH4), black carbon aerosols (BC), tropospheric ozone (O3) and hydrofluorocarbons (HFCs). Recent studies have estimated that by mitigating emissions of CH4, BC, and O3 using available technologies, about 0.5 to 0.6 °C warming can be avoided by mid-21st century. Here we show that avoiding production and use of high-GWP (global warming potential) HFCs by using technologically feasible low-GWP substitutes to meet the increasing global demand can avoid as much as another 0.5 °C warming by the end of the century. This combined mitigation of SLCPs would cut the cumulative warming since 2005 by 50% at 2050 and by 60% at 2100 from the CO2-only mitigation scenarios, significantly reducing the rate of warming and lowering the probability of exceeding the 2 °C warming threshold during this century.
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Atmos. Chem. Phys., 13, 6083–6089, 2013
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The role of HFCs in mitigating 21st century climate change
Y. Xu
, D. Zaelke
, G. J. M. Velders
, and V. Ramanathan
Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA
Program on Governance for Sustainable Development, Bren School of Environmental Science & Management,
UC Santa Barbara, CA 93106, USA
National Institute for Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, the Netherlands
Correspondence to: Y. Xu (
Received: 21 November 2012 – Published in Atmos. Chem. Phys. Discuss.: 18 December 2012
Revised: 16 May 2013 – Accepted: 23 May 2013 – Published: 26 June 2013
Abstract. There is growing international interest in mitigat-
ing climate change during the early part of this century by re-
ducing emissions of short-lived climate pollutants (SLCPs),
in additionto reducing emissions of CO
. The SLCPs include
methane (CH
), black carbon aerosols (BC), tropospheric
ozone (O
) and hydrofluorocarbons (HFCs). Recent studies
have estimated that by mitigating emissions of CH
, BC, and
using available technologies, about 0.5 to 0.6
C warm-
ing can be avoided by mid-21st century. Here we show that
avoiding production and use of high-GWP (global warming
potential) HFCs by using technologically feasible low-GWP
substitutes to meet the increasing global demand can avoidas
much as another 0.5
C warming by the end of the century.
This combined mitigation of SLCPs would cut the cumula-
tive warming since 2005 by 50% at 2050 and by 60% at
2100 from the CO
-only mitigation scenarios, significantly
reducing the rate of warming and lowering the probability of
exceeding the 2
C warming threshold during this century.
1 Introduction
The ozone depleting substances (ODSs) (e.g., chloroflu-
orocarbons (CFCs), hydrochlorofluorocarbons (HCFCs)),
halons, and HFCs are part of a family of gases known as
halocarbons. Halocarbons are used as refrigerants, propel-
lants, cleaning and foam blowing agents, and fire extinguish-
ers, etc. Molina and Rowland (1974) identified the potent
stratospheric ozone depleting effects of CFCs. This was fol-
lowed, within a year, by the discovery of the potent green-
house effect of the halocarbons CFC-11 and CFC-12 (Ra-
manathan, 1975). Many studies confirmed this finding and
estimated that the global warming potential (GWP) of CFC-
11 and CFC-12 (using a 100yr time horizon) at 4750 and
10900 respectively, as summarized by the Intergovernmental
Panel on Climate Change Fourth Assessment Report (Forster
et al., 2007). Ramanathan (1975) set the stage for identifying
numerous other non-CO
greenhouse gases (GHGs) in the at-
mosphere such as CH
and O
among others (see Wang et al.,
1976 and Ramanathan et al., 1985a). The first international
assessment of the climate effects of non-CO
gases was con-
ducted in 1985 (Ramanathan et al., 1985b) and it concluded
that CO
was the dominant contributor to greenhouse forcing
until 1950s, and since the 1960s non-CO
gases have begun
to contribute as much as CO
. A more recent list of the non-
GHGs can be found in Pinnock et al. (1995) and Forster
et al. (2007).
Most of HFCs now in use, along with CH
, O
, and BC
(black carbon aerosols), have relatively short lifetimes in the
atmosphere in comparison with long-lived GHGs, such as
and N
O (nitrous oxide) (e.g., see Smith et al., 2012),
and are therefore referred to as short-lived climate pollutants
(SLCPs). The lifetime of BC is several days to weeks, tro-
pospheric O
is a few months, and CH
is about 12yr. The
global average lifetime, weighted by the production of the
various HFCs now in commercial use, is about 15yr, with
a range of 1 to 50yr (Table 1). Because the lifetimes of the
SLCPs are much shorter than that of CO
, a significant por-
tion of which remains in the atmosphere for centuries to mil-
lennia, the radiative forcing by SLCPs will decrease signif-
icantly within weeks to a few decades after their emissions
are reduced.
Motivated by modeling studies (e.g., Ramanathan and Xu,
2010; Shindell et al., 2012), policy makers are showing
Published by Copernicus Publications on behalf of the European Geosciences Union.
6084 Y. Xu et al.: The role of HFCs in mitigating 21st century climate change
Table 1. Indicative applications using HFCs
HFC Indicative applications Lifetime 100yr GWP
UNEP and WMO (2011) WMO (2011) WMO (2011)
HFC-134a Mobile and stationary air conditioning and refrigeration, foams, 13.4 1370
medical aerosols and cosmetic and convenience aerosol products
HFC-32 In blends for refrigeration and air conditioning 5.2 716
HFC-125 In blends for refrigeration and air conditioning 28.2 3420
HFC-143a In blends for refrigeration and air conditioning 47.1 4180
HFC-152a Foams, aerosol products 1.5 133
HFC-227ea Foams, medical aerosols, fire protection 38.9 3580
HFC-245fa Foams 7.7 1050
HFC-365mfc Foams 8.7 842
HFC-43-10mee Solvents 16.1 1660
HFC-23 is not included in the scenarios discussed here. Although it is currently the second most abundant HFC in the atmosphere, it is assumed that the
majority of this chemical is produced as a byproduct of HCFC-22 production and not because of its use as a replacement for CFCs and HCFCs. Hence, the
emissions of HFC-23 depend on a different set of assumptions than the other HFCs (Velders et al. 2009). Miller and Kuijpers (2011) estimated that HFC-23
emissions increase could contribute 0.014Wm
to radiative forcing in 2050. Therefore, the contributed warming due to potential HFC-23 will be only
about 0.01
C by our estimation.
increasing interest in fast-action climate mitigation strategies
that target SLCPs (Wallack and Ramanathan, 2009; Molina
et al., 2009). Ramanathan and Xu (2010) (hereafter RX10)
concluded that as much as 0.6
C warming can be avoided
by mid-21st century using current technologies to reduce
all four SLCPs, with mitigation of HFCs contributing about
20% (0.1
C) to the avoided warming by 2050. Furthermore,
RX10 also showed that exceeding the 2
C warming thresh-
old can be delayed by three to five decades beyond 2050
by these efforts. Based on an international assessment com-
missioned by the United Nations Environment Programme
(UNEP) and the World Meteorological Organization (WMO)
(UNEP and WMO, 2011), Shindell et al. (2012) used a
3-dimensional climate model to account for reductions in
, O
, and BC emissions (but not HFCs) using mitiga-
tion scenarios similar to those employed in RX10. UNEP
and WMO (2011) as well as Shindell et al. (2012) calcu-
lated the avoided warmingto be0.5(± 0.05)
C by 2070. This
estimate is consistent with RX10, which would also yield
C avoided warming if only CH
, O
, and BC were mit-
igated. All three studies calculated that full implementation
of mitigation measures for these three SLCPs can reduce the
rate of global warming during the next several decades by
nearly 50%. Furthermore, Arctic warming can be reduced
by two-thirds over the next 30yr compared to business as
usual (BAU) scenarios (UNEP and WMO, 2011).
However, with the exception of the RX10 study, HFCs
have thus far not been included in analyses of the temper-
ature mitigation benefit from SLCP mitigation. Even RX10
did not recognize the full potential of the radiative forcing
increase, as shown recently by Velders et al. (2012), due to
an unconstrained use of HFCs toward the end of this century.
Therefore, what has been missing in the previous studies is
the potentially large increase in HFC use. The present study
builds upon RX10 to further account for the newly devel-
oped projections of HFC emissions and provides a detailed
analysis of the implication of HFC mitigation on global tem-
2 Methods
2.1 HFC emission projection
Because of their catalytic destruction of stratospheric ozone,
production and consumption of CFCs, HCFCs and other
ODSs are being phased out under the Montreal Protocol (An-
dersen and Sarma, 2002; Andersen et al., 2007). With the
phase-out of CFCs under the Montreal Protocol completed
in 1996 in developed countries and in 2010 in developing
countries (UNEP, 2010), and with the scheduled phase-out
of HCFCs by 2030 in developed countries, and 2040 in de-
veloping countries (UNEP, 2007), HFCs are increasingly be-
ing used as alternatives in applications that traditionally used
CFCs, HCFCs and other ODSs to meet much of the de-
mand for refrigeration, air conditioning, heating and thermal-
insulating foam production (Velders et al., 2012). HFCs do
not destroy the ozone layer (Ravishankara et al., 1994) but
are potent GHGs (Velders et al., 2009).
The demand for HFCs is expected to increase in both de-
veloped and developing countries, especially in Asia, in the
absence of regulations, as is the demand for HCFCs for feed-
stock (Velders et al., 2009). HFCs are the fastest growing
GHGs in the US, where emissions grew nearly 9 % between
2009 and 2010 compared to 3.6% for CO
(EPA, 2012).
Globally, HFC emissions are growing 10 to 15 % per year
and are expected to double by 2020 (WMO, 2011; Velders et
al., 2012). The presence of HFCs in the atmosphere results
almost completely from their use as substitutes for ODSs
(Table 1).
Atmos. Chem. Phys., 13, 6083–6089, 2013
Y. Xu et al.: The role of HFCs in mitigating 21st century climate change 6085
The future HFC projection in this study is estimated us-
ing (1) the growth rates of gross domestic product (GDP)
and populations from the Special Report on Emissions Sce-
narios (SRES) (IPCC, 2000), and (2) the replacement pat-
terns of ODSs with HFCs and not-in-kind technologies as
observed in the past years in Western countries. We assumed
that these replacement patterns will stay constant and will
hold for developing countries. The European Union regu-
lation (842/2006) aimed at moving away from high-GWP
HFCs is also included in the HFC projections used here.
Readers are referred to Velders et al. (2009) for more de-
tails in HFC scenario development (e.g., emissions by sub-
stance, region and years). Because the projected forcing from
HFC-23 is much smaller than that from intentionally pro-
duced HFCs, it is not included in this study. In spite of poten-
tial large increases in HFC-23 from the continued production
of HCFC-22 for feedstock, the HFC-23 forcing in 2050 is
(Miller and Kuijpers, 2011) and the associated
warming is only about 0.01
2.2 Other emission projection
The future emission scenarios of CO
are adopted from the
Representative Concentration Pathway (RCP, van Vuuren et
al., 2011) database. We take RCP 2.6 (van Vuuren et al.,
2007) as mitigation case and RCP 6.0 (Hijioka et al., 2008)
as BAU case for CO
. CO
emissions in the mitigation case
will decline by half in mid-21st century, while the BAU CO
emissions are projected to continue to increase until 2080.
The peak CO
atmospheric concentration is 660 and 440
ppm under BAU and mitigation cases, respectively. We note
that CO
scenarios under RCP 6.5 and 2.6 may have differ-
ent assumptions with regard to emission sectors and there-
fore the difference between those two pathways may not di-
rectly represent the effect of mitigation efforts. The SLCP
projections, except for HFCs, are retained from RX10. Under
a BAU scenario, CH
emissions are predicted to rise by 40%
in 2030, and BC emissions are projected to increase by 15%
by 2015 and then level off. The mitigation scenarios follow
recommendations from studies by the International Institute
for Applied Systems Analysis (IIASA) (Cofala et al., 2007)
and the Royal Society (2008) that maximum feasible reduc-
tions of air pollution regulations can result in reductions of
50% in CO emissions and 30% in CH
emissions by 2030,
as well as reductions of 50% in BC emissions by 2050.
2.3 Models
The model used in RX10 is an integrated carbon and radi-
ant energy balance model. It adopts the Bern CO
istry model (Joos et al., 1996) to estimate the atmospheric
concentration from emissions. The model links emis-
sions of pollutants with their atmospheric concentrations and
the change in the radiative forcing. The carbon-geochemistry
model is then integrated with an energy balance climate
Fig 1. HFC radiative forcing change (W/m2) since the year of 2005. Note we include both upper 423
(red solid line) and lower limit (red dash line) of HFC growth under BAU scenarios. The 424
scenarios previously adopted in RX10 and from various other sources are shown for reference. 425
Fig. 1. HFC radiative forcing change (W m
) since the year of
2005. Note we include both upper (red solid line) and lower limits
(red dash line) of HFC growth under BAU scenarios. The scenar-
ios previously adopted in RX10 and from various other sources are
shown for reference.
model with a 300 m ocean mixed layer and a climate sen-
sitivity of 0.8 (0.5 to 1.2)
) to simulate the tempo-
ral evolution of global mean surface temperature. The model
also accounts for historical variations in the global mean ra-
diative forcing to the system attributable to natural factors,
GHGs and air pollutants including sulfates, nitrates, carbon
monoxide, ozone, BC, and organic carbons. The model is ca-
pable of simulating the observed historical temperature vari-
ations (Fig. 2), as well as the historical CO
and ocean heat content (Box 1 in RX10).
3 Results and discussions
3.1 Large increase of HFC forcing
The radiative forcing of HFCs in 2008 was small at less
than 1% of the total forcing from long-lived GHGs (WMO,
2011). However, without fast action to limit their growth,
the radiative forcing of HFCs could increase from nearly
in 2010 to up to 0.4Wm
in 2050 (BAU high
in Fig. 1). The 0.4 Wm
is equal to nearly 30 to 45% of
forcing increase by 2050 (if CO
follows BAU and mit-
igation scenarios, respectively; see Sect. 2.2 for scenario de-
scriptions), or about the same forcing contributed by current
emissions from the transportation sector (IEA, 2011).
In the scenarios discussed here, the demand for HFCs for the
period 2050 to 2100 is assumed to maintain at the 2050 lev-
els (assuming complete market saturation), which results in
increasing HFC abundances and radiative forcing past 2050,
with HFC forcing possibly reaching as high as 0.8Wm
2100 (BAU high in Fig. 1). Atmos. Chem. Phys., 13, 6083–6089, 2013
6086 Y. Xu et al.: The role of HFCs in mitigating 21st century climate change
Fig 2. Model simulated temperature change under various mitigation scenarios that include CO
and SLCPs (BC, CH
, HFCs). BAU case (red solid line with spread) considers both high and low 429
estimates of future HFC growths (as shown in red solid and dash lines in Fig. 1). Note this 430
uncertainty of temperature projection related to HFC scenarios is around 0.15°C at 2100. The 431
vertical bars next to the curve show the uncertainty of temperature projection at 2100 due to 432
climate sensitivity uncertainty. For simplicity, we only show the cases of CO
mitigation (red 433
dash line) and full mitigation (black line). 434
Fig. 2. Model simulated temperature change under various miti-
gation scenarios that include CO
and SLCPs (BC, CH
, HFCs).
BAU case (red solid line with spread) considers both high and low
estimates of future HFC growths (as shown in red solid and dash
lines in Fig. 1). Note this uncertainty of temperature projection re-
lated to HFC scenarios is around 0.15
C at 2100. The vertical bars
next to the curve show the uncertainty of temperature projection at
2100 due to climate sensitivity uncertainty. For simplicity, we only
show the cases of CO
mitigation (red dash line) and full mitigation
(black line).
We also calculate HFC forcing from emission data pro-
vided by the RCP database and compare them with our forc-
ing projections. Similar comparisons of future emission and
forcing are also shownin Fig. 5.5 of the WMO (2011) assess-
ment. However, a direct comparison is difficult, because with
the exception of RCP 8.0 (Riahi et al., 2007), the scenarios
include various mitigation policies as assumptions and there-
fore cannot be considered as “BAU” scenarios. The Global
Change Assessment Model (GCAM) group that produces
RCP 4.5 (Wise et al., 2009; Thomson et al., 2011) does,
however, make available a “BAU” scenario (GCAM base-
line in Fig. 1), which does not include explicit mitigation ac-
tions (Smith et al., 2011). As a result, HFC forcing is two
times larger in the GCAM baseline scenario than the asso-
ciated RCP 4.5 scenario. The HFC BAU projections used in
this study are substantially higher over the long-term than the
projections of other studies, including RCP 8.0 and GCAM
baseline. In the GCAM baseline, for example, HFC forcing
increase from 2005 is less than 0.2Wm
in 2100, as com-
pared to 0.5 to 0.8Wm
in our BAU scenarios.
There are several reasons for the discrepancies in HFC
projections. (1) HFC scenarios have not received much at-
tention in the development of the RCP database. Individual
integrated assessment modeling groups have adopted vari-
ous assumptions and techniques in developing those RCP
projections and associated reference scenarios. However, de-
tailed descriptions of HFC projection in RCPs and associ-
ated reference scenarios are not available in relevant papers,
which are more focused on long-lived GHGs. (2) Most, if
not all, of the RCP scenarios for HFCs were developed be-
fore 2007. Therefore, they did not take into account the ac-
celerated HCFC phase-out in both developing and developed
countries agreed by the parties at the 19th Meeting of the Par-
ties to the Montreal Protocol in September 2007, which will
lead to lower future HCFC emissions and higher HFC emis-
sions (Meinshausen et al., 2011). (3) At least some RCP sce-
narios did not take into account the large observed growth in
HFC use and atmospheric concentrations since 2000 (WMO,
2011). The linear growth in RCP scenarios (Fig. 1 and also
see Fig. 3.22 of Clarke et al., 2007) is distinctly different
from the assumptions of a growing market in developing
countries, which was the basis of our HFC scenario. (4) Fi-
nally, another recent HFC scenario up to 2050 (Gschreyet al.,
2011), which includes detailed market analysis, also shows
emissions much higher than RCPs, but smaller than ours.
The smaller emissions in Gschrey et al. (2011) compared to
ours are the result of two assumptions: first, a larger frac-
tion of non-fluorocarbon alternatives in several sectors; and
second, and second, the market saturation in several sectors
after about 2030, 10yr earlier than in our scenarios, which
considered consumption saturation for a few sectors at 2040
(Fig. 1b of Velders et al., 2009) and a complete saturation
after 2050. Note that the emission of HFCs will continue in-
creasing for a short time period after the market saturation at
2050, and the mixing ratio and forcing of HFC will further
grow toward end of 21st century (Fig. 1). We acknowledge
that some RCP models project HFC in a detailed method
(e.g., by gas and sector based on the evolution of multiple
drivers over time including vehicle demand, building air-
conditioning use, etc.). Some RCP models and Gschrey et
al. (2011) have also assumed some emission drivers do not
scale with GDP over the long-term due to saturation effects
(e.g., floor space of buildings), which could be even more
important on a century timescale. The differences in consid-
ering saturation effects may be a reason that our projections
yield larger emissions.
In conclusion, differences in HFC scenarios arise from
large differences in their underlying assumptions and to the
level they take into account recent information. HFC projec-
tions insome RCP scenarios do not use themore recent infor-
mation as in Velders et al. (2009) and Gschrey et al. (2011).
The scenarios in Velders et al. (2009) are based on assump-
tions similar to those of IPCC-SRES with respect to growth
rates in GDP and population, but have incorporated new cur-
rent informationon (1) reported recent increases in consump-
tion of HCFCs in Article 5 (developing) countries of about
20% per year (through 2007), (2) replacement patterns of
HCFCs by HFCs as reported in non-Article 5 (developed)
countries, and (3) accelerated phase-out schedules of HCFCs
in Article 5 and non-Article 5 countries (2007 Adjustment of
the Montreal Protocol). We note that this HFC scenario is not
necessarily a more accurate forecast of future HFC emissions
than other scenarios, but a projection of what can happen if
Atmos. Chem. Phys., 13, 6083–6089, 2013
Y. Xu et al.: The role of HFCs in mitigating 21st century climate change 6087
developed countries continue current practices in replacing
ODSs with HFCs and if developingcountries follow this path
as well.
In contrast to the large increase under BAU scenarios, re-
placing those HFCs currently in use with low-GWP HFC
alternatives that have lifetimes of less than one month can
eliminate future HFC forcing increase (Velders et al., 2012).
Under the mitigation scenario, the total HFC radiative forc-
ing in 2050 would be less than its current value (Mitigation
in Fig. 1). Alternatives with no direct impact on climate, in-
cluding ammonia, carbon dioxide, and hydrocarbons, as well
as low-GWP HFCs and not-in-kind alternatives, are already
in commercial use in a number of sectors. For other sectors,
alternatives are being evaluated or further developed (UNEP,
2011). The calculation of climate mitigation assumes that the
selected alternatives do not compromise energy efficiency,
an assumption that appears reasonable in light of the his-
toric trend of increased energy efficiency when chemicals
are phased out under the Montreal Protocol (Andersen and
Morehouse, 1997; Andersen and Sarma, 2002; Andersen et
al., 2007).
3.2 Implication for global temperature
The simulated temperature trends (Fig. 2) agree with the ear-
lier studies (Shindell et al., 2012; UNEP and WMO, 2011)
that combined mitigation of CH
, BC and O
can miti-
gate 0.5
C of warming by the mid-century. It also agrees
with RX10 that HFCs contribute about 0.1
C to the avoided
warming of 0.6
C by 2050 and that SLCPs are critical for
limiting the warming below 2
mitigation, although
begun in 2015, has very little effect for the near-term (see
difference between red solid line and red dash line in Fig. 2).
Focusing on the longer timescale of the end of the century
(Fig. 2), CO
mitigation plays a major role in reducing addi-
tional warming by as much as 1.1
C by 2100. Next, the com-
bined measures (CO
, CH
, BC and O
) considered in UNEP
and WMO (2011) and Shindell et al. (2012) are not suffi-
cient to limit the warming below 2
C (blue line in Fig. 2),
had these studies included the updated projected HFC growth
patterns of Velders et al. (2009) in their BAU scenarios. Miti-
gation of the potentialgrowth of HFCsis shown to play a sig-
nificant role in limiting the warming to below 2
C and could
contribute additional avoided warming of as much as 0.5
by 2100 (blue and black line in Fig. 2). Using the lower lim-
its of BAU increase of HFC (red dash line in Fig. 1), 0.35
warming will be avoided.
The results are consistent with RX10 for the near-term,
but the avoided warming from HFCs towards the end of the
century is 100% higher in this study, due to the updated
forcing scenarios accounting for the high HFC growth rate
(green lines in Fig. 1 for a comparison with RX10 forcing
scenarios). Replacing HFCs with available low-GWP sub-
stitutes that have a lifetime of one month or less, or with
other materials or technologies, can provide up to 0.35 to
C of warming mitigation by 2100 in the scenarios used
here. The important point to note is that assessing the role
of HFCs in climate change depends on what BAU (i.e., ref-
erence/baseline) scenarios the climate models assume for
HFCs in their simulations. Many climate models assume
much smaller growth of HFC emission, because of the im-
plicit assumption that replacements with low impact on cli-
mate for high-GWP HFCs will be adopted extensively dur-
ing this century, an assumption that largely depends on the
extent of policy interventions, as well as technological and
economic developments. Our study, however, shows that if
current growth rates of high-GWP HFCs continue, the addi-
tional warming from HFCs alone will be as much as 0.5
during this century. The potential temperature mitigation by
the end of this century, from HFC replacement, is in addi-
tion to the 1
C potential mitigation from other SLCP re-
ductions (Fig. 2; also see RX10). When mitigation effort to
reduce high-GWP HFCs is combined with that on BC and
, 0.6
C warming can be avoided by 2050 and 1.5
by 2100 (black solid line vs. red dash line in Fig. 2). This
would cut the cumulative warming since 2005 by 50% at
2050 and by 60% at 2100 from the corresponding CO
mitigation scenarios (red dash line in Fig. 2). Based on our
high HFC growth scenarios, the contribution to the avoided
warming at 2100 due to HFC emission control is about 40%
of that due to CO
emission control. Considering the near-
term (2050) timescale, HFC emission is even more effective
(140% of CO
mitigation) in curbing the warming. Given
the limited knowledge regarding climate sensitivity (0.5 to
)), the absolute valueof projected temperature
at the end of 21st century is also uncertain (vertical bars in
Fig. 2), but the relative contribution of HFC to reducing the
warming is still significant and less subject to such uncer-
4 Conclusions
The concept of “short-lived climate pollutants” highlights
the shorter lifetime of those pollutants (including HFCs) as
compared to long-lived GHGs (including CO
and CFCs).
Our paper demonstrates the benefits of replacing high-GWP
HFCs with low-GWP alternatives, so the overall forcing
and associated warming due to HFC growth can be signifi-
cantly reduced. The results presented here could strengthen
the interest of policymakers in promoting fast-action strate-
gies to reduce SLCPs, including HFCs, as a complement
to immediate action to reduce CO
emissions. There are
several policy options for limiting HFC growth, separate
from those for BC and CH
, including using the Mon-
treal Protocol to phase down the production and consump-
tion of HFCs (Molina et al., 2009; UNEP, 2012a, b), which
would preserve the climate benefits the treaty has already
achieved through its success in phasing out nearly 100 sim-
ilar chemicals (Velders et al., 2007, 2012). Without the Atmos. Chem. Phys., 13, 6083–6089, 2013
6088 Y. Xu et al.: The role of HFCs in mitigating 21st century climate change
Montreal Protocol, the projected radiative forcing by ODSs
would have been roughly 0.65Wm
in 2010 (Velders et al.,
2007), and the global temperature would have been higher
(green line in Fig. 2). It is also important to emphasize that
HFC mitigation should not be viewed as an “alternative”
strategy for avoiding the 2
C warming, but rather as a critical
component of a strategy that also requires mitigation of CO
and the other SLCPs. The focus of this study is on near-term
warming over the next several decades to end of the century.
For the longer-term (century and beyond), mitigation of CO
would be essential for a significant reduction in the warming.
Acknowledgements. The study was supported by the National
Science Foundation (ATM07-21142) and University of California,
San Diego Open Access Fund (Pilot). We thank Nathan Borgford-
Parnell, Stephen O. Andersen, and Dennis Clare for reading the
manuscript; and Allison Thomson and Keywan Riahi for sharing
data. We acknowledge two anonymous reviewers and Steven J.
Smith for their constructive comments that greatly improved the
Edited by: D. Shindell
Andersen, S. O. and Morehouse, E. T.: The Ozone Challenge: In-
dustry and Government Learned to Work Together To Protect
Environment, American Society of Heating, Refrigeration and
Air-Conditioning Engineers (ASHRAE) Journal, 33–36, 1997.
Andersen, S. O. and Sarma, K. M.: Protecting the Ozone Layer: the
United Nations History, Earthscan Press, London, 2002.
Andersen, S. O., Sarma, K. M., and Taddonio, K. N.: Technol-
ogy Transfer for the Ozone Layer: Lessons for Climate Change,
Earthscan Press, London, 2007.
Clarke, L., Edmonds, J., Jacoby, H., Pitcher, H., Reilly, J., and
Richels, R.: Scenarios of Greenhouse Gas Emissions and Atmo-
spheric Concentrations. Sub-report 2.1A of Synthesis and As-
sessment Product 2.1 by the US Climate Change Science Pro-
gram and the Subcommittee on Global Change Research. De-
partment of Energy, Office of Biological & Environmental Re-
search, Washington, DC, USA, 154 pp., 2007.
Cofala J., Amann, M., Klimont, Z., Kupiainen, K., and Hoglund-
Isaksson, L.: Scenarios of global anthropogenic emissions of air
pollutants and methane until 2030, Atmos. Environ., 41, 8486–
8499, 2007.
EPA: Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990–2010, EPA 430-R-12-001, US Environmental Protection
Agency, Washington DC, USA, 2012.
Forster, P. and Ramaswamy, V.: Changes in atmospheric con-
stituents and in radiative forcing. Climate Change 2007: The
Physical Sciences Basis. Contribution of Working Group I to
the Fourth Assessment Report of the Intergovernmental Panel on
Climate Change, edited by: Solomon, S., Qin, D., Manning, M.,
Chen, Z., Marquis, M., Averyt, K. B., Tignor, M., and Miller, H.
L., 129–234, Cambridge Univ. Press, Cambridge, UK, 2007.
Gschrey, B., Schwarz, W., Elsner, C., and Engelhardt, R.: High in-
crease of global F-gas emissions until 2050, Greenhouse Gas
Measurement Management, 1, 85–92, 2011.
Hijioka, Y., Matsuoka, Y., Nishimoto, H., Masui, M., and Kainuma,
M.: Global GHG emissions scenarios under GHG concentration
stabilization targets. J. Global Environ. Eng., 13, 97–108, 2008.
IPCC: Special report on emissions scenarios, Intergovernmental
Panel on Climate Change, Cambridge Univ. Press, Cambridge,
UK and New York, 2000.
emissions from fuel combustion: Highlights, Interna-
tional Energy Agency, Paris, France, 2011.
Joos, F., Bruno, M., Fink, R., Siegenthaler, U., Stocker, T., Le
e, C., and Sarmiento J.: An efficient and accurate representa-
tion of complex oceanic and biospheric models of anthropogenic
carbon uptake, Tellus B Chem. Phys. Meteorol., 48, 397–417,
Meinshausen, M., Smith, S. J., Calvin, K., Daniel, J. S., Kainuma,
M. L. T., Lamarque,J.-F., Matsumoto, K.,Montzka, S. A., Raper,
S. C. B., Riahi, K., Thomson, A., Velders, G. J. M., van Vu-
uren, D. P. P.: The RCP Greenhouse Gas Concentrations and
their Extensions from 1765 to 2500, Clim. Change, 109, 213–
241, doi:10.1007/s10584-011-0156-z, 2011.
Miller, B. R. and Kuijpers, L. J. M.: Projecting future HFC-23 emis-
sions, Atmos. Chem. Phys., 11, 13259–13267, doi:10.5194/acp-
11-13259-2011, 2011.
Molina, M. and Rowland, F. S.: Stratospheric Sink for Chloroflu-
oromethanes: Chlorine Atom-Catalyzed Destruction of Ozone,
Nature, 249, 810–814, 1974.
Molina M., Zaelke, D., Sarma, K. M., Andersen, S. O., Ra-
manathan, V., and Kaniaru, D.: Reducing abrupt climate change
risk using the Montreal Protocol and other regulatory actions to
complement cuts in CO
emissions, Proc. Natl. Acad. Sci., 106,
20616–20621, 2009.
Pinnock, S., Hurley, M. D., Shine, K. P., Wallington, T. J., and
Smyth, T. J.: Radiative forcing of climate by hydrochlorofluoro-
carbons and hydrofluorocarbons, J. Geophys. Res., 100, 23227–
23238, 1995.
Ramanathan V.: Greenhouse Effect Due to Chlorofluorocarbons:
Climatic Implications, Science, 190, 50–52, 1975.
Ramanathan V. and Xu, Y.: The Copenhagen Accord for limit-
ing global warming: Criteria, constraints, and available avenues,
Proc. Natl. Acad. Sci., 107, 8055–8062, 2010.
Ramanathan, V., Cicerone, R. J., Singh, H. B., and Kiehl, J. T.:
Trace gas trends and their potential role in climate change, J.
Geophys. Res., 90, 5547–5566, 1985a.
Ramanathan, V., Callis, L., Cess, R., Hansen, J., Isaksen, I., Kuhn,
W., Lacis, A., Luther, F., Mahlman, J., Reck, R., and Schlesinger,
M.: Trace Gas Effects on Climate, Assessment of our under-
standing of the processes controlling its present distribution and
change, WMO, Global Ozone Research and Monitoring Project,
Report, no. 16. Report commissioned by NASA/Federal Avia-
tion Administration, NOAA, WMO, UNEP, Commission of the
European Communities and Bundesminisiterium Fur Forschung
Technologie, Chapter 16, Volume III of Atmospheric Ozone
1985, 821–863, 1985b.
Ravishankara, A. R., Turnipseed, A. A., Jensen, N. R., Barone, S.,
Mills, M., Howard, C. J., and Solomon, S.: Do hydrocarbons de-
stroy stratospheric ozone?, Science, 263, 71–75, 1994.
Atmos. Chem. Phys., 13, 6083–6089, 2013
Y. Xu et al.: The role of HFCs in mitigating 21st century climate change 6089
Riahi, K., Gruebler, A., and Nakicenovic, N.: Scenarios of long-
term socio-economic and environmental development under cli-
mate stabilization, Technol. Forecast. Soc. Change, 74, 887–935
Royal Society: Ground-level ozone in the 21st century: Future
trends, impacts and policy implications, The Royal Society, Lon-
don, UK, 23–54, 2008.
Shindell, D., Kuylenstierna, J. C. I., Vignati, E., van Dingenen, R.,
Amann, M., Klimont, Z., Anenberg, S. C., Muller, N., Janssens-
Maenhout, G., Raes, F., Schwartz, J., Faluvegi, G., Pozzoli, L.,
Kupiainen, K., H
oglund-Isaksson, L., Emberson, L., Streets, D.,
Ramanathan, V., Hicks, K., Oanh, N. T. K., Milly, G., Williams,
M., Demkine, V., and Fowler, D.: Simultaneously Mitigating
Near-Term Climate Change and Improving Human Health and
Food Security, Science, 335, 183–189, 2012.
Smith, S. J., West, J. J., and Kyle, P.: Economically Consistent
Long-Term Scenarios for Air Pollutant and Greenhouse Gas
Emissions, Clim. Change, 108, 619–627, 2011.
Smith, S. M., Lowe, J. A., Bowerman, N. H. A., Gohar, L. K., Hunt-
ingford, C., and Allen, M. R.: Equivalence of greenhouse-gas
emissions for peak temperature limits, Nature Clim. Change 2,
535–538, 2012.
Thomson A. M., Calvin, K. V., Smith, S. J., Kyle, G. P., Volke, A.
C., Patel, P. L., Delgado Arias, S., Bond-Lamberty, B., Wise, M.
A., Clarke, L. E., and Edmonds, J. A.: RCP4.5: A Pathway for
Stabilization of Radiative Forcing by 2100, Clim. Change, 109,
77–94, doi:10.1007/s10584-011-0151-4, 2011.
UNEP: Adjustments agreed by the Nineteenth Meeting of the Par-
ties relating to the controlled substances in group I of An-
nex C of the Montreal Protocol (hydrochlorofluorocarbons), in
Report of the Nineteenth Meeting of the Parties to the Mon-
treal Protocol on Substances that Deplete the Ozone Layer,
UNEP/OzL.Pro.19/7, United Nations Environment Program
Ozone Secretariat, Nairobi, Kenya, 2007.
UNEP: Report of the Twenty-Second Meeting of the Parties to
the Montreal Protocol on Substances that Deplete the Ozone
Layer, UNEP/Ozl.Pro.22/9, United Nations Environment Pro-
gram Ozone Secretariat, Nairobi, Kenya, 2010.
UNEP: HFCs: A Critical Link In Protecting Climate and the Ozone
Layer, United Nations Environment Programme, Nairobi, Kenya,
UNEP: Proposed amendment to the Montreal Protocol submitted by
the Federated States of Micronesia, UNEP/OzL/Pro.WG.1/32/5,
United Nations Environment Program, Nairobi, Kenya. 2012a.
UNEP: Proposed amendment to the Montreal Protocol submit-
ted by Canada, Mexico and the United States of America,
UNEP/OzL.Pro.WG.1/32/6, United Nations Environment Pro-
gram, Nairobi, Kenya, 2012b.
UNEP and WMO: Integrated Assessment of Black Carbon and
Tropospheric Ozone, United Nations Environment Program and
World Meteorological Organization, Nairobi, Kenya, 2011.
van Vuuren, D., den Elzen, M., Lucas, P., Eickhout, B., Strengers,
B., van Ruijven, B., Wonink, S., and van Houdt, R.: Stabiliz-
ing greenhouse gas concentrations at low levels: an assessment
of reduction strategies and costs, Clim. Change, 81, 119–159,
doi:10.1007/s/10584-006-9172-9, 2007.
van Vuuren, D. P., Edmonds, J., Kainuma, M., Riahi, K., Thomson,
A., Hibbard, K., Hurtt, G. C., Kram, T., Krey, V., Lamarque, J.-
F., Masui, T., Meinshausen, M., Nakicenovic, N., Smith, S. J.,
and Rose, S. K.: TheRepresentativeConcentration Pathways: An
Overview, Clim. Change, 109, 5–31, 2011.
Velders, G. J. M., Andersen, S. O., Daniel, J. S., Fahey, D. W., and
McFarland, M.: The Importance of the Montreal Protocol in Pro-
tecting the Climate, Proc. Natl. Acad. of Sci., 104, 4814–4819,
Velders, G. J. M., Fahey, D. W., Daniel, J. S., McFarland, M., and
Andersen, S. O.: The LargeContributionofProjectedHFCEmis-
sions to Future Climate Forcing, Proc. Natl. Acad. of Sci., 106,
10949–10954, 2009.
Velders, G. J. M., Ravishankara, A. R., Miller, M. K., Molina, M.
J., Alcamo, J., Daniel, J. S., Fahey, D. W., Montzka, S. A., and
Reimann, S.: Preserving Montreal Protocol Climate Benefits by
Limiting HFCs, Science, 335, 922–923, 2012.
Wallack, J. and Ramanathan, V.: The other climate changers, why
black carbon also matters, Foreign Aff., 88, 105–113, 2009.
Wang, W. C., Yung, Y. L., Lacis, A. A., Mo, T., and Hansen, J. E.:
Greenhouse effect due to manmade perturbations of trace gases,
Science, 194, 685–690, 1976.
Wise, M. A., Calvin, K. V., Thomson, A. M., Clarke, L. E., Bond-
Lamberty, B., Sands, R. D., Smith, S. J., Janetos, A. C., and Ed-
monds, J. A.: Implications of Limiting CO
Concentrations for
Land Use and Energy, Science, 324, 1183–1186, 2009.
WMO: Report No. 52: Scientific Assessment of Ozone De-
pletion: 2010, World Meteorological Organization Global
Ozone Research and Monitoring Project, Geneva, Switzerland,
available at Panels/SAP/
Scientific Assessment 2010/00-SAP-2010-Assement-report.
pdf, 2011. Atmos. Chem. Phys., 13, 6083–6089, 2013
... In this study, the environmental impact of HFC-134a emissions was analysed from two perspectives: climate impact and the production of the degradation product TFA. First, the global radiative forcing increase and global surface temperature increase caused by HFC-134a emissions are used to analyse their climate impact, and the estimation methods [27]. The specific formulae are as follows: ...
... Here, ∆RF is the radiative forcing changes of HFC-134a emissions (W m −2 ) in the North China Plain. C i−1,E and RF j,E are the global average mixing ratio and radiative forcing when the HFC-134a emissions in the North China Plain are E i,N and C i−1,0 , and RF j,0 are the global average mixing ratios and radiative forcing when the HFC-134a emissions in the North China Plain are 0. τ and RE represent life (years) and radiation effi- [27]. ...
... the methods used byFang et al., (2016) [13] andXu et al., (2013) ...
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1,1,1,2-tetrafluoroethane (HFC-134a) is a potent greenhouse gas that can be degraded to produce trifluoroacetic acid (TFA), a degradation product that has an impact on aquatic ecology, so its emission has been a continuous concern worldwide. Existing studies mainly estimate the global- or national-scale emissions of HFC-134a, and there are relatively few studies on regional emissions, all of which used the top-down method. By establishing a regional-scale bottom-up emission inventory and comparing it with the regional-scale top-down estimation results, regional emissions can be verified and their emission characteristics and environmental impacts can be analysed. HFC-134 emissions were estimated for the first time in the North China Plain using the emission factor method, and spatiotemporal characteristics and environmental impacts were analysed for the period of 1995 to 2020. The results showed that the cumulative HFC-134a emissions were 88 (73–103) kt (126 Mt CO2-eq), which have led to an increase in global radiative forcing of 1.1 × 10−3 (0.9 × 10−3–1.3 × 10−3) W m−2, an increase in global surface temperature of 8.9 × 10−4 °C, and a cumulative TFA production of 7.5 (6.2–8.9) kt as of 2020. The major sources of HFC-134a emissions are the refrigeration and air conditioning sector, which involves the automotive air conditioning (MAC), industrial and commercial refrigeration, and air conditioning (ICR) sub-sectors. China joined the Kigali Amendment in 2021 to phase down HFCs and proposed the goal of carbon neutrality by 2060. The North China Plain is a region undergoing rapid economic development, with a relatively high proportion of GDP (29%) and car ownership (23%) in 2020. Additionally, HFC-134a emissions accounted for about 20% of the total emissions in China. Therefore, HFC-134a emissions and their environmental impact on the North China Plain should not be ignored.
... These fluids are characterized, among other things, by being low-GWP refrigerants. According to Xu et al. (2013), replacing HFCs with low-GWP substances could avoid an increase in temperature of 0.6 • C by 2050. Therefore, it is essential to consider the use of alternative refrigerants to conventional ones to contribute to the reduction of global warming. ...
... The phaseout of high global warming potential (GWP) 1 refrigerants, comprised of low and high GWP hydrofluorocarbons (HFCs) [4][5][6], has been recently mandated by US law [7,8] and international agreements [9,10]. For example, the commonly used refrigerant R-410a (GWP = 2088), comprised of an equimass mixture of the relatively low GWP HFC-32 (difluoromethane, GWP = 674) and the high GWP HFC-125 (pentafluoroethane, GWP = 3500), is scheduled for phaseout [11]. ...
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The Kigali Amendment introduced a new family of chemical compounds, which do not contribute to stratospheric ozone depletion but present a high global warming potential, under the watch of the Montreal Protocol in 2016. Earlier this year, a press note from the World Meteorological Organization entitled “Ozone layer recovery is on track, helping avoid global warming by 0.5°C” caught our attention because of the wrong conclusions that can be potentially drawn by laypersons due to an apparent linkage of ozone depletion and global warming problems. Public communication of the Montreal Protocol since the Kigali Amendment should be more careful than ever to avoid lessening the social perception of the threat of climate change, particularly considering that society already has a distorted representation of these problems, assuming causal relations between ozone depletion and climate change, that could lead to unfounded optimism towards the climate crisis.
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China is the largest greenhouse gas emitter in the world and has committed to mitigating global warming through achieving carbon neutrality by 2060. However, detailed information on China’s historical and projected emissions of fluorinated greenhouse gases, with high global warming potentials, is lacking. Here we establish a comprehensive and up-to-date inventory of China’s fluorinated greenhouse gas emissions and find that they show an accelerating growth rate, increasing from 5.5 to 221 million tons CO2-equivalent per year from 1990 to 2019. China has become the world’s largest emitter of fluorinated greenhouse gases and contributed 93% of the global emission increase during the period 1990−2019. We find that total emissions of fluorinated greenhouse gases from China are projected to increase to 506–1356 million tons CO2-equivalent per year in 2060 if there is no regulation, which is larger than the projected CO2 emissions under China’s carbon neutrality commitment for 2060.
Ozone-depleting substances (ODSs), which also contribute to global warming, have been controlled by the Montreal Protocol (MP) since 1987. China joined the MP in 1991 and began reducing production and consumption of ODSs in the country, leading to a decrease in emissions of ODSs. Based on the Intergovernmental Panel on Climate Change guidelines, the latest emission factors and actual consumption in China (MP scenario), both the historical banks and the historical emissions of ODSs and substitute hydrofluorocarbons (HFCs) during 1980-2020 were calculated. To understand the reduction in ODS and HFC emissions by implementing the MP, we also estimated China's virtual emissions (NMP, i.e., the amount of ODS emissions without the MP) over the same period. The avoided cumulative ODS consumption and emission values of 10.8 and 5.8 (4.8-6.9) million tonnes (Mt) of CFC-11-equivalent (eq), respectively, were estimated by comparing the two scenarios. Furthermore, 26 (22-33) giga tonnes (Gt) of CO2-eq emissions, equivalent to an increase of 0.031 W m-2 radiative forcing, were estimated to be avoided by 2020, which will prevent an additional 0.025 °C increase in temperature. The MP implemented by China has resulted in substantial environmental benefits over the last 30 years. However, owing to the massive use of HFCs as substitutes, the cumulative emissions reached 2286 Mt. CO2-eq during 1990-2020, and it will be challenging to phase down HFCs in the environment after China ratified the Kigali Amendment in 2021.
Global hydrofluorocarbon (HFC) cumulative emissions will be more than 20 Gt CO2-equiv during 2020-2060 and have a non-negligible impact on global warming even in full compliance with the Kigali Amendment (KA). Fluorochemical manufacturers (including multinationals) in China have accounted for about 70% of global HFC production since 2015, of which about 60% is emitted outside China. This study built an integrated model (i.e., DECAF) to estimate both territorial and exported emissions of China under three scenarios and assess the corresponding climate effects as well as abatement costs. Achieving near-zero territorial emissions by 2060 could avoid 23 ± 4 Gt CO2-equiv of cumulative territorial emissions (compared to the 2019 Baseline scenario) during 2020-2060 at an average abatement cost of 9 ± 6 USD/t CO2-equiv. Under the near-zero emission (including territorial and abroad) pathway, radiative forcing from HFCs will peak in 2037 (60 ± 6 mW/m2) with a 33% peak reduction and 8 years in advance compared to the path regulated by the KA, and the radiative forcing by 2060 will be lower than that in 2019. Accelerated phase-out of HFC production in China could provide a possibility for rapid global HFC abatement and achieve greater climate benefits.
Full-text available
A Reference Case (RC) scenario for emissions of HFC-23 from co-production during HCFC-22 manufacture over the next 25 years is presented. Offered as a template rather than a prediction, this model projects current production practices and existing abatement frameworks to yield insights into how atmospheric composition and radiative forcing might change with and without additional efforts to constrain HFC-23 emissions. Assuming that no additional abatement measures are implemented, emissions for year 2035 in this Reference Case would rise to 24 ktonnes yr<sup>−1</sup>, (cf., 8.6 ktonnes yr<sup>−1</sup> in 2009), the atmospheric abundance of HFC-23 would rise to 50 ppt, which is a 121 % increase over the 2009 observed abundance, and HFC-23 would be expected to contribute a radiative forcing of 9 mW m<sup>−2</sup> (cf., 4 mW m<sup>−2</sup> in 2009). Under such a scenario, the HFC-23 emission growth rate would be a continuation of the historical trend of ∼0.2 ktonnes yr<sup>−2</sup> until 2030, after which the growth is projected to quadruple as the Montreal Protocol phase-out of HCFC production for dispersive use concludes and HFC-23 thermal decomposition in the projects of the Clean Development Mechanism (CDM) comes to a scheduled end while growth in the production of HCFC-22 for feedstock use continues to climb with projected GDP growth. Two opposite variations regarding the future renewal of CDM projects are examined for their impact on projected emissions and abundance, relative to the Reference Case scenario.
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Climate policies address emissions of many greenhouse gases including carbon dioxide, methane, nitrous oxide and various halogen-containing compounds. These are aggregated and traded on a CO2-equivalent basis using the 100-year global warming potential (GWP100); however, the GWP100 has received scientific and economic criticism as a tool for policy. In particular, given international agreement to limit global average warming to 2°C, the GWP100 does not measure temperature and does not clearly signal the need to limit cumulative CO2 emissions. Here, we show that future peak temperature is constrained by cumulative emissions of several long-lived gases (including CO2 and N2O) and emission rates of a separate basket of shorter-lived species (including CH4). For each basket we develop an emissions-equivalence metric allowing peak temperature to be estimated directly for any emissions scenario. Today's emissions of shorter-lived species have a lesser impact on ultimate peak temperature than those nearer the time of peaking. The 2°C limit could therefore be met by setting a limit to cumulative long-lived CO2-equivalent emissions while setting a maximum future rate for shorter-lived emissions.
'Imagine the pride of earning the Nobel Prize for warning that CFCs were destroying the ozone layer. Then imagine that citizens, policymakers, and business executives heeded the warning and transformed markets to protect the earth. This book is the story of why we can all be optimistic about the future if we are willing to be brave and dedicated world citizens.' MARIO MOLINA, Nobel Laureate in Chemistry and Professor, University of California This book tells how the Montreal Protocol, the most successful global environmental agreement so far, stimulated the development and worldwide transfer of technologies to protect the ozone layer. Technology transfer is the crux of the 230 international environmental treaties and is essential to fighting climate change. While debate rages about obstacles to technology transfer, until now there has been no comprehensive assessment of what actually works to remove the obstacles. The authors, leaders in the field, assess over 1000 technology transfer projects funded under the Montreal Protocol?s Multilateral Fund and the Global Environment Facility, and identify lessons that can be applied to technology transfer for climate change.
Stabilization scenario analysis revealed that when a low GHG stabilization level is set, the GHG emission peak needs to be reached as soon as possible and efforts should be made to reduce GHG emissions drastically by 2050 and thereafter. Furthermore, sensitivity analysis revealed two important results. First, the results of simulations using different discount rates for two different stabilization levels indicated that the more stringent the constraints, the more limited the choice of emission paths will be. In particular, to achieve a 2.0°C increase in the global mean temperature above the preindustrial level using 2-10% discount rates, a 15% emission range in 2020 and a 4% emission range in 2050 could be permitted for Kyoto Protocol gas. Second, the results of simulations using different climate sensitivities indicated that to achieve the goal of a 2.0°C global mean temperature increase with 50% or 66.6% probability, Kyoto Protocol gas emissions need to be reduced by 78% and 83%, respectively.