Content uploaded by Tom Kram
Author content
All content in this area was uploaded by Tom Kram
Content may be subject to copyright.
PERSPECTIVES
The next generation of scenarios for climate
change research and assessment
Richard H. Moss
1
, Jae A. Edmonds
1
, Kathy A. Hibbard
2
, Martin R. Manning
3
, Steven K. Rose
4
, Detlef P. van Vuuren
5
,
Timothy R. Carter
6
, Seita Emori
7
, Mikiko Kainuma
7
, Tom Kram
5
, Gerald A. Meehl
2
, John F. B. Mitchell
8
,
Nebojsa Nakicenovic
9,10
, Keywan Riahi
9
, Steven J. Smith
1
, Ronald J. Stouffer
11
, Allison M. Thomson
1
,
John P. Weyant
12
& Thomas J. Wilbanks
13
Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of
Earth’s climate system and its likely response to human and natural influences. The implications of climate change for the
environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on
how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in
future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential
consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such
as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information
among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate
some of the most challenging and important questions about climate change confronting the global community.
To improve understanding of the complex interactions of the
climate system, ecosystems, and human activities and condi-
tions, the research community develops and uses scenarios.
These scenarios provide plausible descriptions of how the
future might unfold in several key areas—socioeconomic, technological
and environmental conditions, emissions of greenhouse gases and
aerosols, and climate. When applied in climate change research,
scenarios help to evaluate uncertainty about human contributions to
climate change, the response of the Earth system to human activities, the
impacts of a range of future climates, and the implications of different
approaches to mitigation (measures to reduce net emissions) and
adaptation (actions that facilitate response to new climate conditions).
Traditionally, model-based scenarios used in climate change
research have been developed using a sequential process focused on a
step-by-step and time-consuming delivery of information between
separated scientific disciplines. Now, climate change researchers from
different disciplines have establisheda new coordinatedparallel process
for developing scenarios. This starts with four scenarios of future radi-
ative forcings (the change in the balance between incoming and out-
going radiation to the atmosphere caused by changes in atmospheric
constituents, such as carbon dioxide). Using this starting point, the
parallel process will encourage research that will characterize a broad
range of possible futureclimate conditions, taking into account recent
climate observations and new information about climate system pro-
cesses. Studies will give more attention to evaluating adaptation needs
and strategies, exploring mitigation options, and improving under-
standing of potentially large feedbacks (that is, impacts of climate
change such as melting of permafrost or dieback of forests that cause
further changes in climate).
Central to the new parallel process is the concept that the four
radiative forcing pathways can be achieved by a diverse range of socio-
economic and technological development scenarios. Among other
issues, the parallel process facilitates exploration of the question
‘What are the ways in which the world could develop in order to reach
a particular radiative forcing pathway?’ An immediate consequence of
this new approach will be heightened collaboration between impacts,
adaptation and vulnerability research, and climate and integrated
assessment modelling (Box 1). This will improve the analysis of com-
plex issues, such as the costs, benefits and risks of different policy
choices and climate and socioeconomic futures. The parallel process
will reduce the time lags between the creation of emissions scenarios,
their use in climate modelling, and the application of the resulting
climate scenarios in research on impacts, adaptation and vulnerability.
This Perspective provides an overview of how scenarios are used in
climate change research, and summarizes the new process initiated
with ‘representative concentration pathways’ (RCPs) that will pro-
vide a framework for modelling in the next stages of scenario-based
research. Additional information can be found in refs 1–4.
Alternative futures
The use of scenarios originated in military planning and gaming, and
in the early 1960s was extended into strategic planning in businesses
and other organizations where decision makers wanted to analyse, in
a systematic way, the implications of investment and other strategic
decisions with long-term consequences
5–8
. The goal of working with
scenarios is not to predict the future, but to better understand un-
certainties in order to reach decisions that are robust under a wide
range of possible futures
9
.
1
Joint Global Change Research Institute, Pacific Northwest National Laboratory/University of Maryland, 5825 University Research Court, Suite 3500, College Park, Maryland 20740,
USA.
2
National Center for Atmospheric Research, Climate and Global Dynamics Division, 1850 Table Mesa Drive, Boulder, Colorado 80305, USA.
3
New Zealand Climate Change
Research Institute, Victoria University of Wellington, PO Box 600, Wellington, New Zealand.
4
Electric Power Research Institute, 2000 L Street NW, Suite 805, Washington DC 20036,
USA.
5
Netherlands Environmental Assessment Agency, Postbus 303, 3720 AH Bilthoven, The Netherlands.
6
Finnish Environment Institute, Box 140, Mechelininkatu 34a, Helsinki
00251, Finland.
7
National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba 305-8506, Japan.
8
Met Office, Fitzroy Road, Exeter, Devon EX1 3PB, UK.
9
International Institute
for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria.
10
Vienna University of Technology, Karlsplatz 13, A-1040 Vienna, Austria.
11
Geophysical Fluid Dynamics
Laboratory, National Oceanic and Atmospheric Administration, Princeton, New Jersey 08542, USA.
12
Stanford University, Stanford, California 94305, USA.
13
Environmental Sciences
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Vol 463j11 February 2010jdoi:10.1038/nature08823
747
Macmillan Publishers Limited. All rights reserved
©2010
In climate change research, scenarios describe plausible trajectories
of climate conditions and other aspects of the future. A variety of
techniques have been used, including temporal and spatial analogues
of future climates and model-based scenarios, which are the focus of
this Perspective
10
. The earliest model-based ‘scenarios’ were stylized
representations of increases in the atmospheric concentrations of
carbon dioxide (a greenhouse gas that retains energy radiating from
the Earth’s surface). Initially a doubling or quadrupling of carbon
dioxide was used as an input to ‘force’ early climate models. These
scenarios provided a coherent basis for using climate models to
address the question, ‘If carbon dioxide concentrations increased by
a specified amount or rate, how might the climate system respond?’
Over time, an increasingly broad array of scenarios has been
developed to address different components of the issue
11
; we show
in Fig. 1 an historical perspective on the development of scenarios,
some notable applications, and some context. Today, scenarios
represent major driving forces, processes, impacts (physical, eco-
logical and economic) and potential responses important for inform-
ing climate change policy (Fig. 2). Within the overall category of
scenarios, several types are prominent in climate change research.
Emissions scenarios. Emissions scenarios are descriptions of potential
future discharges to theatmosphere of substances that affect the Earth’s
radiation balance, such as greenhouse gases and aerosols. Along with
information on other related conditions such as land use and land
cover, emissions scenarios provide inputs to climate models. They
are produced with integrated assessment models (Box 1) based on
assumptions about driving forces, such as patterns of economic and
population growth, technology development, and other factors. Over
time, the information provided by integrated assessment models and
used in climate models has become increasingly comprehensive,
including time-dependent emissions of radiatively significant gases
and particles, precursor pollutant compounds, and land cover and use.
In addition to their use as inputs to climate models, emissions
scenarios are used to explore alternative energy and technology
futures. This allows exploration of what changes in technologies,
economic development, policy, or other factors would be required
to shift emissions from a baseline to a lower path—for example,
keeping greenhouse gas concentrations (or global average surface air
temperature increases) below a specified level. They can be used to
analyse the need for and the value of technology, and the implications
of choices to limit radiative forcing to prescribed limits. Although
scenario outputs include emissions and land use/cover, they also
include drivers of change, such as patterns and rates of economic
growth, demographic change, technology, policy and other factors
that are important for the assessment of the impacts of climate
change
12
.
Emissions scenarios for climate change research are not forecasts
or predictions, but reflect expert judgments regarding plausible
future emissions based on research into socioeconomic, environ-
mental, and technological trends represented in integrated assess-
ment models. Emissions scenarios for climate change research do
not track ‘short-term’ fluctuations, such as business cycles or oil
market price volatility. Instead, they focus on long-term (decades
to centuries) trends in energy and land-use patterns. The long-term
focus is necessary for evaluating the slow response of the climate
system (centuries) to changing concentrations of greenhouse gases.
The long-term focus also reflects the long time horizon for retiring
and replacing many components of energy and economic infrastruc-
ture. Uncertainty in emissions scenarios results from the inherent
uncertainty of future socioeconomic and technology conditions,
uncertainty in the policy environment, and differences in representa-
tions of processes and relationships across integrated assessment
models, among other factors. An underlying key issue is whether
probabilities can be usefully associated with scenarios or different
Context/institutional
development
Notable applications
1896 Arrhenius’
estimates CO2-
induced
warming 64
1960 Keeling
shows
atmospheric
CO2 is
increasing 65
1967 Modelled
estimates of
climate
sensitivity 62
1969 Coupled
ocean–atmosphere
GCM 63
1970s Scenarios
used to explore
natural resource
sustainability 23–26
1980s Scenarios
become
mainstream in
futures
research 27–29
1980 World
Climate
Research
Program
established
1988 GCM
simulations using
time-dependent
(transient) scenarios
indicate the signal of
anthropogenic climate
warming would soon
emerge from natural
variability 66
1983 Villach
Conference
reviews
agricultural
and ecosystem
impacts with
scenarios 67
1985 Second
Villach Conference
estimates mid 21st
century rise of
global mean
temperature
greater than any in
human history 68
1990 IPCC
SA90
emissions
scenarios 36
1990 IPCC First
Assessment Report
uses analogue and
equilibrium climate
scenarios for
impact assessment
1988 IPCC
established
1992 IPCC IS92
scenarios 30
1991 Impact
studies
published
based on
transient
climate
scenarios 66, 69
1994 IPCC
impact
assessment
guidelines 70
Scenario development
Figure 1
|
Timeline highlighting some notable developments in the creation and use of emissions and climate scenarios. The entries are illustrative of the
overall course of model-based scenario development (blue) and application (beige) described in this Perspective, and also give some context (green); they do
PERSPECTIVES NATUREjVol 463j11 February 2010
748
Macmillan Publishers Limited. All rights reserved
©2010
levels of radiative forcing; for example, the probability that concen-
trations will stabilize above or below a specified level
13–15
.
Climate scenarios. Climate scenarios are plausible representations
of future climate conditions (temperature, precipitation and other cli-
matological phenomena). They can be produced using a variety
of approaches including: incremental techniques where particular cli-
matic (or related) elements are increased by plausible amounts; spatial
and temporal analogues in which recorded climate regimes that may
resemble the future climate are used as example future conditions; other
techniques, such as extrapolation and expert judgment; and techniques
that use a variety of physical climate and Earth system models, including
regional climate models
10
. All of these techniques continue to play a
useful role in development of scenarios, with the appropriate choice of
method depending on the intended use of the scenario
16
,butmost
major advances are expected with model-based approaches. There is
a notable increase in interest in regional-scale climate scenarios and
projection methods, especially for impact and adaptation assessment
17
.
Environmental scenarios. Analysis of the potential impact of a par-
ticular climate scenario requires environmental scenarios of eco-
logical and physical conditions at greater detail than is included in
climate models. These scenarios focus on changes in environmental
conditions other than climate that may occur regardless of climate
change. Such factors include water availability and quality at basin
levels (including human uses), sea level rise incorporating geological
and climate factors, characteristics of land cover and use, and local
atmospheric and other conditions affecting air quality. Climate
change merges with these factors, and in many cases, the potential
impact of climate change and effectiveness of adaptation options
cannot be understood without examining these interactions
16,18
.
Vulnerability scenarios. Finally, scenarios of factors affecting vul-
nerability, such as demographic, economic, policy, cultural and insti-
tutional characteristics are needed for different types of impact
modelling and research. This information is crucial for evaluating
the potential of humankind to be affected by changes in climate, as
well as for examining how different types of economic growth and
social change affect vulnerability and the capacity to adapt to potential
impacts. Although some of these factors can be modelled and applied
at regional or national scales
19
, for the most part data at finer spatial
resolution are required. An increasing body of literature, including
some using integrated assessment models, is exploring alternative
methods for the quantitative and qualitative ‘downscaling’ of these
vulnerability factors in a way that is consistent with the socioeconomic
assumptions underlying global emissions scenarios
20–22
.
Earlier scenario work. Antecedents of contemporary global scenarios
were developed in ‘futuresstudies’ that exploredthe long-term sustain-
ability of natural resources
23–26
and the implications of global energy
needs for future CO
2
emissions and concentrations
27–29
. The Inter-
governmental Panel on Climate Change (IPCC) has used emissions
and climate scenarios as a central component of its work of assessing
climate change research. It stimulated development of the field by
commissioning several sets of emissions scenarios for use in its reports.
In earlier emissions scenario exercises, the IPCC convened authors and
modellers, provided terms of reference, and approved the scenarios
through an intergovernmental process that took several years. The
1990 IPCC scenario A (SA90)
30
set explored four emissions pathways,
including a ‘business as usual’ future and three policy scenarios. They
were followed by the 1992 IPCC scenarios (IS92)
31
that played out the
implications of uncertainties in economic growth, population and tech-
nology in a number of business as usual energy and economic futures.
The latest set of scenarios from the IPCC, contained in the Special
Report on Emissions Scenarios (SRES)
32
, investigated the uncertainty
of future greenhouse gas and short-lived pollutant emissions given a
wide range of driving forces. Some of the cases explored the implica-
tions of economic convergence between developed and developing
1995
Scenario
generator for
non-specialists 71
1995
Comparison of
global vegetation
model results
using equilibrium
GCM 2 × CO2 72
1995 IPCC
Second
Assessment
Report uses
equilibrium
climate
scenarios in
impact report
1996 Country
studies of
impacts 73
1998
Emissions
scenarios
database
published 74
1998 IPCC
regional impacts
assessment
(using IS92) 75
1999 SRES,
no climate policies
included 32
2000 Pattern
scaling of IS92-
based climate
projections to
emulate SRES 76 2001
Comprehensive
multi-model
assessment of
mitigation
scenarios 77
2001 IPCC
Third
Assessment
Report impact
results using
IS92 scenarios
2001 Socio-
economic
‘vulnerability’
scenarios 78
2004 Regional
projections of
seasonal
temperature and
precipitation based
on SRES 79
2005 Scenarios
and model
comparison of
mitigation
options for non-
CO2 GHGs 80
2005
Millennium
Ecosystem
Assessment
2007 IPCC ‘new
scenarios’ expert
meeting 3 and model
comparison of
economic and
technological pathways
to stabilize radiative
forcing at several
levels 48
2007 IPCC Fourth
Assessment
Report uses SRES
and IS92 scenarios
for impacts
2007 IAMC founded
2009 RCPs
released, starting
‘parallel phase’ of
new scenario
process
2009 UK
probabilistic
national climate
projections 81
and extension
of methodology
for probabilistic
climate
projections 82
2009 World
Climate
Conference 3
discusses
development
of capacity to
respond to the
needs of users
of climate
information
worldwide.
not provide a comprehensive account of all major scenarios and significant studies or assessments that have used them. See Supplementary Information for
details. GCM, general circulation model; GHG, greenhouse gas; IAMC, Integrated Assessment Modelling Consortium.
NATUREjVol 463j11 February 2010 PERSPECTIVES
749
Macmillan Publishers Limited. All rights reserved
©2010
countries. Unlike previous emissions scenarios, the quantitative SRES
projections were complemented by ‘storylines’ or narratives of the
future, which facilitated the interpretation of the scenarios. Unlike
previous scenarios that were developed using only one or two models,
the SRES scenarios were produced through an ‘open process’ involving
many different modellingteams. The IS92 and SRES scenarios assumed
there were no policy actions to mitigate climate change.
Many other organizations have developed scenarios that include
greenhouse gas emissions and their interactions with other socio-
economic and environmental systems (for example, the International
Energy Agency
33
and the Millennium Ecosystem Assessment
34
)orhave
played a substantial role in shaping the scenario development process
(the Energy Modelling Forum). Overviews of scenario development in
climate change research are available
32,35,36
(see also timeline in Fig. 1).
Motivations for new scenarios
Although the previous IPCC scenarios and process have been produc-
tive, new scenarios and a new process for selecting and using them are
needed. Nearly a decade of new economic data, information about emer-
ging technologies, and observations of environmental factors such as
land use and land cover change should be reflected in new scenarios
37,87
.
End users,including policymakers, have new information needsthat
require changes in scenario focus. For example, there is a high level of
interest in climate scenarios that explore different approaches to miti-
gation in addition to the traditional ‘no climate policy’ scenarios. As a
result, an increasing number of scenarios are being developed to
explore conditions consistent with managed long-run climate out-
comes, including a 2 uC maximum global average surface temperature
increase over pre-industrial levels, as well as ‘overshoot’ scenarios in
which radiative forcing peaks and then declines to a target level
38–42
.In
addition, increasing attention to the impacts of climate change and the
need for adaptation has spawned an interest in climate scenarios that
focus on the next two to three decades with higher spatial and temporal
resolution and improved representation of extreme events. Analysis of
adaptation also requires development of socioeconomic scenarios suit-
able to support analysis of vulnerability.
Box 1 jModels and frameworks
Scenarios are generated and used by three broad types of models and
analytic frameworks in climate change research: integrated assessment
models, climate models, and models and other approaches used to help
assess impacts, adaptation and vulnerability.
(1) Integrated assessment models represent key features of human
systems, such as demography, energy use, technology, the economy,
agriculture, forestry and land use. They also incorporate simplified
representations ofthe climatesystem, ecosystems, andin some cases,climate
impacts
12
. These simplified representations are calibrated against more
complex climate and impact models. Because of their breadth, these models
integrate information needed to study the interactions of human systems
(including potential climate policies) and environmental processes that affect
climate change and its impacts. Integrated assessment models typically
disaggregate the world into a dozen or more regions with time steps of about a
decade. Integrated assessment models are used to develop emissions
scenarios, estimate the potential economic impacts of climate change and the
costs and benefits of mitigation, simulate feedbacks, and evaluate
uncertainties. Because they are increasingly comprehensive and include more
detail about air pollutant emissions and land use, these models are increasingly
important for research on the interaction of climate change with other policy
objectives (such as air-pollution control and biodiversity protection).
(2) Climate models
44,84
are numerical representationsof the Earth’s natural
systems used to study how climate responds to changes in natural and
human-induced perturbations. There are a wide variety and complexity of
climate models. Atmosphere
–
ocean general circulation models are the most
complex physical climate models, and include components that simulate
interactions of the atmosphere, ocean, land and sea ice. They divide the
atmosphere and oceans into thousands of grid cells, and include interactive
land-surface and biophysical processes. Regional climate models focus on
subcontinental scale geographies at finer resolution. Earth system models are
based on physical climate models, and include additional ecological and
chemical processes, such as the land and ocean carbon cycle, vegetation and
atmospheric chemistry,which respondto changes in climate simulated by the
model. Earth system models of intermediate complexity represent many of
the key systems and processes, but with simplified equations and reduced
spatial resolution. These models are useful for sensitivity experiments,
questions involving long timescales (hundreds to thousands of years), or when
a large number of simulations are required. Simple climate models incorporate
fewer detailed processes in the atmosphere
–
ocean system and at coarser
spatial scales. They are useful for exploring key uncertainties and have been
incorporated into many integrated assessment models.
(3) Assessing impacts, adaptation and vulnerability to climate change
depends on a widearray of methods and tools that includes both quantitative
and qualitative approaches. Prominent approaches include observations,
modelling, assessment techniques that engage stakeholders in participatory
processes, economic evaluation methods and decision analysis
85
.The
models and frameworks span the range from biophysical to economic, and
explore the consequences of changes in climate for climate-sensitive
resources and activities, such as agriculture, water resources, human health,
ecosystems and coastal infrastructure. These frameworks inform decision
makers of the potential risks and opportunities presented by climate change,
and provide a means of evaluating the impacts associated with different
magnitudes of climate change and the comparative effectiveness of various
response strategies and management options. When impact models include
representations of changes in fluxes ofgreenhouse gases tothe atmosphere
from natural and managed systems, they are useful for studying climate
system ‘feedbacks’; for example, from forest dieback or permafrost melting.
The figure depicts the domains of the three sets of models and
frameworks
86
, and illustrates that the models increasingly are covering
overlapping substantive domains, which underscores the importance of
coordination and consistency in using scenarios.
Energy The economy
Agriculture and
forestry
Health
Human
settlement and
infrastructure
Sea level rise
Integrated assessment
models
Imapacts, adaptation and
vulnerability
Climate models
Water
Ecosystems
Atmospheric
processes
Cryosphere
Oceans
Terrestrial
carbon
cycle
PERSPECTIVES NATUREjVol 463j11 February 2010
750
Macmillan Publishers Limited. All rights reserved
©2010
Scientific advances also motivate interest in new scenarios within
the scientific community. Interest in modelling future climate condi-
tions nearer to a long-term equilibrium across components of the
climate system, such as the oceans and the ice sheets, has created a
demand for emissions scenarios to extend well beyond the conven-
tional 2100 end-point
2,43
. Simultaneously, climate models are becom-
ing more comprehensive and incorporating the oceanic and terrestrial
carbon cycle, aerosols, atmospheric chemistry, ice sheets and dynamic
vegetation
44–46
. As more physical processes are simulated, more
detailed emissions scenarios are required, along with higher resolution
and more consistent land-use and land-cover data and projections.
Finally, increasing the overlap in the substantive domains of climate,
impact and integrated assessment models (Box 1) creates a demand for
harmonization of assumptions and data on some initial conditions,
within the limits posed by historical and observational uncertainties.
Apart from responding to new opportunities and information
needs, a new process for developing scenariosis needed in part because
the IPCC decided at its twenty-fifth session in 2006 not to commission
another set of emissions scenarios, leaving new scenario development
to the research community. IPCC instead limited its role to catalysing
and assessing the large and growing scenario literature. The research
community responded by, among other things, creating this new
process to provide cross-disciplinary coordination. Finally, a new
process that shortens development time and leads to greater coordi-
nation will facilitate additional scientific advances, including
increased understanding of different types of feedbacks and improved
synthesis of research on adaptation, mitigation and damages incurred
and avoided by different policy options.
Redesigned scenario process
The earlier sequential approach. Until now, scenarios were
developed and applied sequentially in a linear causal chain that
extended from the socioeconomic factors that influence greenhouse
gas emissions to atmosphericand climate processes to impacts (Fig. 3).
This sequential process involved developing emissions scenarios
based on different socioeconomic futures, estimating concentrations
and radiative forcing from emissions, projecting the ensuing climate,
and then using those scenarios in impact research. The process led to
inconsistency because of delays between the development of the
emissions scenarios, their use in climate modelling, and the availabil-
ity of the resulting climate scenarios for impact research and assess-
ment. For example, work on the SRES scenarios
32
started in 1997 and
took approximately three years to complete (Fig. 1). The first climate
model results using these scenarios as inputs were assessed in the 2001
IPCC Third Assessment Report, but not until 2007, when the IPCC
published its Fourth Assessment Report, was a more complete set of
SRES-driven climate scenarios available and impact, adaptation and
vulnerability research using these scenarios assessed by IPCC. By this
time, results from a new generation of climate models were being
assessed in the same report, thus creating inconsistencies between the
new climate scenarios and the older ones used in the impact studies.
This complicated the synthesis of results on issues such as costs and
benefits, and created challenges when comparing feedbacks from
different models.
The parallel approach. To shorten the time between the development
of emissions scenarios and the use of the resulting climate scenarios in
impact research, as well as to address the key information needs of
users more effectively, the integrated assessment, climate and impact
research communities have cooperated to devise an alternative ‘par-
allel’ approach for creating and using scenarios (Fig. 4). Rather than
starting with detailed socioeconomic storylines to generate emissions
and then climate scenarios, the parallel process begins with the iden-
tification of important characteristics for scenarios of radiative
forcings for climate modelling, the most prominent of which is the
level of radiative forcing in the year 2100. These radiative forcing
trajectories are not associated with unique socioeconomic or emissions
scenarios, and instead can result from different combinations of eco-
nomic, technological, demographic, policy and institutional futures
Climate variability
and change
Solar
radiation
Atmospheric
composition
H2O, CO2, CH4, N2O, O3, etc.
Aerosols
Volcanoes
Clouds
Atmosphere–
ice interaction
Heat
exchange
Evaporation
precipitation
Terrestrial
radiation
Water
cycle Carbon
cycle
Ecosystems
Human
contributions
and responses
Industries
Agriculture
Cities
Transportation
Land surface
Vegetation–soil
interaction
Vegetation
Atmosphere–
biosphere
interaction
Sea ice
Oceans
Ocean circulation, sea levels,
biogeochemistry
Land-use/land-cover change
Ice
sheet
Glaciers
Rivers
Figure 2
|
Major natural and anthropogenic processes and influences on
the climate system addressed in scenarios. The climate system consists of
five interacting components: the atmosphere, the hydrosphere, the
cryosphere, the land surface and the biosphere. Scenarios of emissions and
other drivers are used to assess the impact of a range of human activities on
these components. Changes in climate described in climate scenarios are
major drivers of changes in both natural and human systems. Impacts on
ecosystems, natural resources, economic activities and infrastructure, and
human well-being, depend not only on climate change, but also on other
changes in the environment (depicted in environmental scenarios) and the
capacity of societies and economies to buffer and adapt to impacts
(addressed in scenarios of vulnerability and adaptive capacity). Closer
integration of scenarios is required to address feedback loops and other
issues, such as the ecological and economic implications of different sets of
adaptation and mitigation policies. Figure from ref. 83.
NATUREjVol 463j11 February 2010 PERSPECTIVES
751
Macmillan Publishers Limited. All rights reserved
©2010
(for comparisons of how different emissions scenarios generated with
different integrated assessment models stabilize at specified target
levels, see refs 47, 48).
Climate models require data on the time-evolving emissions or
concentrations of radiatively active constituents, and some have
additional requirements for information about the time-evolving
paths for land use and land cover. The research community identified
a specific emission scenario (including data on land use and land
cover) from the peer-reviewed literature as a plausible pathway
towards reaching each target radiative forcing trajectory (Table 1;
the selection process and criteria are described more fully below).
These were given the label ‘representative concentration pathways’
(RCPs). The word ‘representative’ signifies that each RCP provides
only one of many possible scenarios that would lead to the specific
radiative forcing characteristics. The term ‘pathway’ emphasizes that
not only the long-term concentration levels are of interest, but also
the trajectory taken over time to reach that outcome. In summary, the
new parallel process starts with the selection of four RCPs, each of
which corresponds to a specific radiative forcing pathway.
In the ‘parallel phase’ of the process, climate and integrated assess-
ment modellers will work simultaneously rather than sequentially.
The climate modellers will conduct new climate model experiments
and produce new climate scenarios using the time series of emissions
and concentrations from the four RCPs. The focus on a few, well-
spaced RCPs will produce discernible climate change outcomes from
one RCP to another, save computational resources, and thus make it
possible to conduct additional new types of experiments.
At the same time as the climate modellers are preparing simula-
tions with the RCPs, the integrated assessment modellers will develop
an ensemble of new socioeconomic and emissions scenarios. Because
this work is done in parallel rather than sequentially, the process is
shortened by the time previously devoted to up-front development of
emissions scenarios. The new ensemble of integrated assessment
model scenarios will constitute an important complement to the
RCPs, because they will help to identify the range of different tech-
nological, socioeconomic and policy futures that could lead to a
particular concentration pathway and magnitude of climate change.
This will encourage new research into novel approaches to meet
Integration of climate
and socio-economic
scenarios
• Integrated
scenarios
• Pattern scaling
(climate)
• Downscaling of
climate and
socio-economic
scenarios
• …
Radiative forcing
New research
and assessments
• Impact,
adaptation,
and
vulnerability
studies
• Climate
change
feedbacks
• Model
development
• …
General
characteristcs
•
Broad range
of
forcing in 2100
•
Shape of radiative
forcing over time
Representative
concentration
pathways (RCPs)
(four pathways from
existing literature)
• Greenhouse gases
• Short-lived gases
and aerosols
• Land cover/use
New socio-economic and
emissions scenarios;
vulnerability storylines
• Adaptation
• Mitigation
• Stabilization
• Overshoots
• …
Climate scenarios
• Near-term (2035)
• Long-term (2100+)
• Regional climate
modelling
• Pattern scaling methods
2008 2009 2010 2011 2012 2013
Consistent
with RCPs
Independent
of the RCPs
Year
Figure 4
|
The parallel process. This figure depicts the process of
developing new scenarios that will be used in future climate change research
and impacts assessments. The process began with identification of radiative
forcing characteristics that support modelling of a wide range of possible
future climates. Representative concentration pathways (RCPs) were
selected from the published literature to provide needed inputs of emissions,
concentrations and land use/cover for climate models. In parallel with
development of climate scenarios based on the RCPs, new socio-economic
scenarios (some consistent with the radiative forcing characteristics used to
identify the RCPs and some developed to explore completely different
futures and issues) will be developed to explore important socio-economic
uncertainties affecting both adaptation and mitigation. Using a variety of
tools and methods, such as pattern scaling, the new socio-economic
scenarios will be integrated with the new climate scenarios. New research
using the integrated scenarios will explore adaptation, mitigation and other
issues such as feedbacks, using consistent assumptions. This research will
provide insights into the costs, benefits and risks of different climate futures,
policies and socio-economic development pathways.
Socio-
economic
scenarios
• Population
• GDP
• Energy
• Industry
•
Transportation
• Agriculture
• …
Emissions
scenarios
• Greenhouse
gases (CO2,
CH4, N2O, …
• Aerosols and
chemically
active gases
(SO2, BC, OC,
CO, NOx,
VOCs
)
• Land use and
land cover
Radiative
forcing
scenarios
• Atmospheric
concentrations
•
Carbon cycle –
including ocean
and terrestrial
uxes
• Atmospheric
chemistry
Climate
model
scenarios
• Temperature
• Precipitation
• Humidity
• Soil moisture
• Extreme
events
• …
Impact,
adaptation,
vulnerability
studies
•
Coastal zones
•
Hydrology and
water resources
• Ecosystems
• Food security
• Infrastructure
• Human health
• …
Figure 3
|
Sequential approach. This figure depicts the simple linear chain
of causes and consequences of anthropogenic climate change. Scenarios were
developed on the basis of this sequence, and handed from one research
community to the next in a lengthy process that led to inconsistencies. GDP,
gross domestic product; BC, black carbon; OC, organic carbon; VOCs,
volatile organic compounds. Figure adapted from ref. 11.
PERSPECTIVES NATUREjVol 463j11 February 2010
752
Macmillan Publishers Limited. All rights reserved
©2010
targets identified by policy makers. In addition, the integrated assess-
ment modellers will develop entirely new scenarios with different
radiative forcing pathways to explore additional issues and un-
certainties. For example, new reference scenarios will be developed
to explore alternative demographic, socioeconomic, land use, and
technology scenario backgrounds. Scenarios will becreated to explore
alternativestabilization levels, including higher overshoot pathways, as
well as the technology, institutional, policy and economic conditions
associated with these pathways. Other scenarios will be developed to
explore uncertainties in processes such as the terrestrial carbon cycle,
the ocean carbon cycle and the atmospheric chemistry of aerosols. A
variety of new regionally based scenarios will be developed using
regional models by research teams in developing and transition-
economy countries. The process by which new scenarios will be pro-
duced and the nature of coordination across research teams is not
specified here and remains to be determined.
The socioeconomic assumptions underlying the new emissions
scenarios (along with information about the spatial distribution of
these characteristics, when possible) will be used to develop scenarios
of factors affecting vulnerability, and will then be paired with climate
model results to provide consistent inputs for impact, adaptation and
vulnerability research. It is an open research question how wide a
range of socioeconomic conditions could be consistent with a given
forcing pathway, including its ultimate level, pathway over time and
spatial pattern; however, the range of underlying socioeconomic
scenarios that are consistent is potentially very wide (carbon cycle
uncertainties are among the major unknowns affecting scenario
development
46
).
A significant portion of the new research anticipated to result from
the RCPs and the subsequent process will be assessed in the IPCC’s
Fifth Assessment Report, now under way and scheduled for release
during 2013 and 2014.
Selection process for the RCPs
A careful selection process was used to identify the RCPs, using
criteria that reflected the needs of both climate scenario developers
and users
3
. As a user of the RCPs and the ensuing research, the IPCC
requested the development of new scenarios compatible with the
literature of reference and mitigation scenarios and helped catalyse
the selection process. The criteria established by the research com-
munity included compatibility ‘with the full range of stabilization,
mitigation, and reference emissions scenarios available in the current
scientific literature’
43
; a manageable and even number of scenarios (to
avoid the inclination with an odd number of cases to select the central
case as the ‘best estimate’); an adequate separation of the radiative
forcing pathways in the long term in order to provide distinguishable
forcing pathways for the climate models; and the availability of model
outputs for all relevant forcing agents and land use. The scientific
community used these criteria to identify four radiative forcing path-
ways, and a new Integrated Assessment Modelling Consortium
(IAMC), comprising 45 participating organizations (http://www.
iamconsortium.org), then assembled a list of candidate scenarios
for each radiative forcing level from the peer-reviewed literature.
The selection process relied on previous assessment of the literature
conducted by IPCC Working Group III during development of the
Fourth Assessment Report
49
. Of the 324 scenarios considered, 32 met
the selection criteria and were able to provide data in the required
format. An individual scenario was then selected for each RCP
(Table 1). The final RCP selections (RCP2.6, RCP4.5, RCP6.0 and
RCP8.5) were made on the basis of discussions at an IPCC expert
Table 1
|
The four RCPs
Name Radiative forcing Concentration
(p.p.m.)
Pathway Model providing RCP*Reference
RCP8.5.8.5Wm
22
in 2100 .1,370 CO
2
-equiv. in 2100 Rising MESSAGE
55,56
RCP6.0,6Wm
22
at stabilization after 2100 ,850 CO
2
-equiv. (at stabilization after 2100) Stabilization without
overshoot
AIM
57,58
RCP4.5,4.5Wm
22
at stabilization after 2100 ,650 CO
2
-equiv. (at stabilization after 2100) Stabilization without
overshoot
GCAM
48,59
RCP2.6Peak at ,3Wm
22
before 2100 and
then declines
Peak at ,490 CO
2
-equiv. before 2100 and
then declines
Peak and decline IMAGE
60,61
*MESSAGE, Model for Energy Supply Strategy Alternatives and their General Environmental Impact, International Institute for Applied Systems Analysis, Austria; AIM, Asia-Pacific Integrated
Model, National Institute for Environmental Studies, Japan; GCAM, Global Change Assessment Model, Pacific Northwest National Laboratory, USA (previously referred to as MiniCAM); IMAGE,
Integrated Model to Assess the Global Environment, Netherlands Environmental Assessment Agency, The Netherlands.
0
1
2
3
4
5
6
7
8
9
10
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Radiative forcing (W m–2)
GCAM 4.5
IMAGE 2.6
AIM 6.0
MESSAGE 8.5
–20
0
20
40
60
80
100
120
Emissions (Gt CO2)
GCAM 4.5
IMAGE 2.6
AIM 6.0
MESSAGE 8.5
Year
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Year
ab
Figure 5
|
Representative concentration pathways. a, Changes in radiative
forcing relative to pre-industrial conditions. Bold coloured lines show the
four RCPs; thin lines show individual scenarios from approximately 30
candidate RCP scenarios that provide information on all key factors
affecting radiative forcing from ref. 47 and the larger set analysed by IPCC
Working Group III during development of the Fourth Assessment Report
49
.
b, Energy and industry CO
2
emissions for the RCP candidates. The range of
emissions in the post-SRES literature is presented for the maximum and
minimum (thick dashed curve) and 10th to 90th percentile (shaded area).
Blue shaded area corresponds to mitigation scenarios; grey shaded area
corresponds to reference scenarios; pink area represents the overlap between
reference and mitigation scenarios.
NATUREjVol 463j11 February 2010 PERSPECTIVES
753
Macmillan Publishers Limited. All rights reserved
©2010
meeting in September 2007, a subsequent open review of proposed
selections involving many modelling teams and users, and the re-
commendation of an ad hoc committee convened to review alterna-
tives for the lowest RCP
50
.
The IAMC coordinated preparation of the RCP data in consultation
with the climate modelling and impact research communities
4,51
.The
regional and spatial RCP data for the climate simulations is publicly
available through the IAMC-RCP database (http://www.iiasa.ac.at/
web-apps/tnt/RcpDb)
Figure 5 illustrates how the selected RCPs represent the literature in
terms of radiative forcing (Fig. 5a) and energy and industry CO
2
emissions (Fig. 5b). The selected set of RCPs spans the range of radi-
ative forcing scenarios in the published literature at September 2007.
For energy and industry CO
2
emissions, RCP8.5 represents the 90th
percentile of the reference emissions range, while RCP2.6 represents
pathways below the 10th percentile of mitigation scenarios. They are
also similarly representative of emissions of greenhouse gases and
particles other than CO
2
(refs 3, 47, 49 and 51).
The RCPs provide a starting point for new and wide-ranging
research. However, it is important to recognize their uses and limits.
They are neither forecasts nor policy recommendations, but were
chosen to map a broad range of climate outcomes. The RCPs cannot
be treated as a set with consistent internal logic. For example, RCP8.5
cannot be used as a no-climate-policy reference scenario for the other
RCPs because RCP8.5’s socioeconomic, technology and biophysical
assumptions differ from those of the other RCPs.
New products and collaborations
Two sets of climate projections will be developed using the RCPs, one
focusing on the near term (to 2035) and the other extending to 2100
and beyond (the Coupled Model Intercomparison Project, Phase 5
(CMIP5) was used to coordinate the experimental design for climate
modelling leading to the Fifth Assessment Report
43
). The near-term
climate projections (mainly comprising ‘decadal predictions’
52
) will
use the single mid-range RCP4.5, because the radiative forcing in the
different RCPs does not diverge appreciably until after this time
period (Fig. 5a). Because multiple scenarios do not need to be run
to span radiative forcing uncertainties, it is possible to run the models
at higher resolution and to prepare larger ensembles (a group of
model experiments used to analyse uncertainty) to improve under-
standing of likely extremes, thereby aiding evaluation of impacts and
adaptation needs for the coming decades. Another set of runs will
provide long-term climate projections to the year 2100, with some
pathways extended to 2300. These extended pathways will be used
for comparative analysis of the long-term climate and environmental
implications of different mitigation scenarios or pathways. ‘Pattern-
scaling’ methods, which use the outcomes of simple climate models
to scale the patterns of climate change produced by complex climate
models to correspond to different emissions scenarios, will be further
evaluated and developed
53,54
.
The new process will increase collaboration among researchers
working on impacts, adaptation and vulnerability with climate and
integrated assessment modellers. One area of collaboration is prepara-
tion of narrative storylines and quantitative vulnerability scenarios
that are coordinated with emissions scenarios, thus encouraging
more impact research that is coordinated explicitly with emissions
and climate scenarios. This will extend the use of socioeconomic
scenarios, which previously have been used more to project green-
house gas emissions than to assess adaptive capacity and vulnerability.
The narratives will provide an interpretative tool for relating the
scenarios to conditions that affect vulnerability at the local and
regional scales at which many impact studies are undertaken. In addi-
tion, downscaled socioeconomic data for consistent, comparable
research on impacts, adaptation and vulnerability will be developed
and evaluated. Results from impact studies using the RCPs will feed
back into climate and integrated assessment modelling.
New climate-policy-intervention scenarios will provide insights
on reducing or stabilizing concentrations of greenhouse gases. For
example, it is anticipated that scenarios will consider land-use and
land-cover choices that include bioenergy production in a world that
is also adapting to climate change. Much work is expected to focus on
low stabilization levels and overshoot scenarios in response to grow-
ing policy interest (Table 1 and Fig. 5a).
Another anticipated advance is the development of integrated
Earth system models that incorporate integrated assessment models,
climate models and impact models. Whereas integrated Earth system
models will not replace the three existing classes of models, they will
bring them closer together than ever before and enable new insights
into the challenge of integrating adaptation and mitigation in climate
change risk management.
Concluding comments
This new generation of scenarios will improve society’s understand-
ing of plausible climate and socio-economic futures. The importance
of the new scenarios is matched by the importance of the increased
level of communication and collaboration across different groups of
researchers.
The new process is only a first step toward the goal of integrating
the now separate tasks of developing scenarios, making projections
and evaluating the impact of the projections. Next steps for further
strengthening the process include establishing mechanisms for
ongoing coordination and information exchange, integrating data
and information systems, and improving support for users. Institu-
tions for coordination and knowledge management across groups
working on impacts, adaptation and vulnerability need to be
strengthened. In addition, the scenario process will need to continue
to evolve to increase the involvement of researchers and users from
developing countries to focus additional attention on crucial inter-
actions among development strategies, adaptation and mitigation.
These steps will improve the climate change impact and response
knowledge base, contribute to the development of socioeconomic
scenarios as a tool for assessing climate change risks and vulner-
abilities, and increase the use of climate scenarios as one starting
point for impact and response analysis.
Realizing the potential benefits of the new process also depends on
a number of scientific advances. Improvement in the representation
of the terrestrial carbon cycle in climate and integrated assessment
models is necessary to reconcile how human use of land resources
interacts with potential climate change impacts on, for instance,
vegetation and carbon cycling. If decadal prediction is to become
skilful, progress in understanding the physical climate system and
new approaches for data assimilation and initialization of models are
needed. Communicating decadal predictions in a way that is useful to
society at large is also a great challenge. Developing new approaches
for making socioeconomic scenarios more useful for research on
adaptive capacity and vulnerability is essential to improving our
ability to compare the consequences of adaptation and mitigation
strategies. Managing the cascade of uncertainties that span different
types of scenarios and improving characterization of uncertainties
and probabilities for ranges of future forcing and climate change is
necessary to make scenarios more useful to decision makers.
Although scenarios do not offer a crystal ball for the future, the new
coordinated approach for developing and applying them in climate
change research will yield valuable insights into the interaction of
natural and human-induced climate processes, and the potential costs
and benefits of different mixes of adaptation and mitigation policy.
1. Meehl, G. A. & Hibbard, K. A. A Strategy for Climate Change Stabilization
Experiments with AOGCMs and ESMs (WCRP Informal Report No. 3/2007, ICPO
Publication No. 112, IGBP Report No. 57, World Climate Research Programme,
Geneva, 2007).
2. Hibbard, K. A., Meehl, G. A., Cox, P. & Friedlingstein, P. A strategy for climate
change stabilization experiments. Eos 88,217, 219, 221 (2007).
PERSPECTIVES NATUREjVol 463j11 February 2010
754
Macmillan Publishers Limited. All rights reserved
©2010
3. Moss, R. H. et al. Towards New Scenarios for Analysis of Emissions, Climate Change,
Impacts,and ResponseStrategies (IPCC Expert M eeting Report, IP CC, Geneva, 200 8).
4. van Vuuren, D. P. et al. Work plan for data exchange between the integrated
assessment and climate modeling community in support of phase-0 of scenario
analysis for climate change assessment (representative community pathways).
Æhttp://www.aimes.ucar.edu/docs/RCP_handshake.pdfæ(6 October 2008).
5. Bradfield, R., Wright, G., Burta, G., Carnish, G. & Van Der Heijden, K. The origins
and evolution of scenario techniques in long range business planning. Futures 37,
795
–
812 (2005).
6. Jefferson, M. in Beyond Positive Economics? (ed. Wiseman, J.) 122
–
159
(Macmillan, 1983).
7. Kahn, H. & Weiner, A. The Year 2000: A Framework for Speculation on the Next
Thirty-three Years (Macmillan, 1967).
8. World Energy Council. Energy for Tomorrow’s World (Kogan Page, London, 1993).
9. Schwartz, P. The Art of the Long View: Planning for the Future in an Uncertain World
(Doubleday, 1996).
10. Mearns, L. O. et al. in Climate Change 2001: The Physical Science Basis (eds
Houghton, J. T., Ding, Y. & Griggs, D. J.) 739
–
768 (Cambridge Univ. Press, 2001).
11. Parson, E. A. et al. Global Change Scenarios: Their Development and Use (Sub-report
2.1B of Synthesis and Assessment Product 2.1, US Climate Change Science
Program and the Subcommittee on Global Change Research, Department of
Energy, Office of Biological & Environmental Research, Washington DC (2007).
12. Weyant, J. et al. in Climate Change 1995: Economic and Social Dimensions of Climate
Change (eds Bruce, J. P., Lee, H. & Haites, E. F.) 367
–
398 (Cambridge Univ. Press,
1996).
13. Schneider, S. H. What is ‘‘dangerou s’’ climate change? Nature 411, 17
–
19 (2001).
14. Grubler, A. & Nakicenovic, N. Identifying dangers in an uncertain climate. Nature
412, 15 (2001).
15. Pittock, A. B., Jones, R. N. & Mitchell, C. D. Probabilities will help us plan for
climate change. Nature 413, 249 (2001).
16. Carter, T. R. et al. General Guidelines on the Use of Scenario Data for Climate Impact
and Adaptation Assessment (Task Group on Data and Scenario Support for Impact
and Climate Assessment (TGICA), IPCC, Geneva, 2007).
17. Christensen, J. H. et al. in Climate Change 2007: The Physical Science Basis (eds
Solomon, S., Qin, D. & Manning, M.) 847
–
940 (Cambridge Univ. Press, 2007).
18. Carter, T. R. et al. in Climate Change 2001: Impacts, Adaptation and Vulnerability
(eds McCarthy, J. J., Canziani, O. F., Leary, N. A., Dokken, D. J. & White, K. S.)
145
–
190 (Cambridge Univ. Press, 2001).
19. Malone, E. L. & Brenkert, A. L. in The Distributional Effects of Climate Change: Social
and Economic Implications (eds Ruth, M. & Ibarraran, M.) 8
–
45 (Elsevier Science,
2009).
20. Gaffin, S. R., Rosenzweig, C., Xing, X. & Yetman, G. Downscaling and geo-spatial
gridding of socio-economic projections from the IPCC Special Report on
Emissions Scenarios (SRES). Glob. Environ. Change 14, 105
–
123 (2004).
21. Grubler, A. et al. Regional, national, and spatially explicit scenarios of
demographic and economic change based on SRES. Technol. Forecast. Soc. Change
74, 980
–
1029 (2006).
22. Van Vuuren, D. P., Lucas, P. & Hilderink, H. Downscaling drivers of global
environmental change. Enabling use of global SRES scenarios at the national and
grid levels. Glob. Environ. Change 17, 114
–
130 (2007).
23. Meadows, D. et al. The Limits to Growth (Universe Books, 1972).
24. Leontief, W. The Future of the World Economy: A Study on the Impact of Prospective
Economic Issues and Policies on the International Development Strategy (United
Nations, New York, 1976).
25. Herrera, A. et al. Catastrophe or New Society? A Latin American World Model (IDRC,
Ottawa, 1976).
26. Mesarovic, M. & Pestel, E. Mankind at the Turning Point (Dutton, 1974).
27. Ha
¨fele, W., Anderer, J., McDonald, A. & Nakicenovic, N. Energy in a Finite World:
Paths to a Sustainable Future (Ballinger, 1981).
28. Robertson, J. The Sane Alternative
–
A Choice of Futures (River Basin, 1983).
29. Svedin, U. & Aniansson, B. Surprising Futures: Notes From an International Workshop
on Long-term World Development (Swedish Council for Planning and Coordination
of Research, Stockholm, 1987).
30. Response Strategies Working Group. in Climate Change: The IPCC Scientific
Assessment (eds Houghton, J. T., Jenkins, G. J. & Ephraums J. J.) 329
–
341
(Cambridge Univ. Press, 1990).
31. Leggett, J., Pepper, W. J. & Swart, R. J. in Climate Change 1992: The Supplementary
Report to the IPCC Scientific Assessment (eds Houghton, J. T., Callander, B. A. &
Varney, S. K.) 69
–
95 (Cambridge Univ. Press, 1992).
32. Nakic
´enovic
´,N.,et al. Special Report on Emissions Scenarios: A Special Report of
Working Group III of the Intergovernmental Panel on Climate Change (Cambridge
Univ. Press, 2000).
33. World Energy Outlook (International Energy Agency, Paris, 2009).
34. Millennium Ecosystem Assessment. Ecosystems and Human Well-being: Scenarios,
Vol. 2 (eds Carpenter, S. R. et al.) xix
–
551 (Island Press, 2005).
35. Alcamo, J. et al. in Climate Change 1994: Radiative Forcing of Climate Change and an
Evaluation of the IPCC IS92 Emission Scenarios (eds Houghton, J. T. et al.) 247
–
304
(Cambridge Univ. Press, 1995).
36. Carter, T. R. et al. in Climate Change 2007: Impacts, Adaptation and Vulnerability
(eds Parry, M. L., Canziani, O. F., Palutikof, J. P., van der Linden, P. J. & Hanson, C.
E.) 133
–
171 (Cambridge Univ. Press, 2007).
37. Hurtt, G. C. et al. Harmonization of global land-use scenarios for the period1500-
2100 for IPCC-AR5. iLEAPS Newsl. 7, 6
–
8 (2009).
38. Clarke, L. & Weyant, J. Introduction to the EMF Special Issue on climate change
control scenarios. Energy Econ. 31, S63
–
S81 (2009).
39. Huntingford, C. & Lowe, J. Overshoot scenarios and climate change. Science 316,
829 (2007).
40. Wigley, T. M. L., Richels, R. & Edmonds, J. in Human-Induced Climate Change: An
Interdisciplinary Perspective (eds Schlesinger, M. et al.)84
–
92 (Cambridge Univ.
Press, 2007).
41. Calvin, K. et al. Limiting climate change to 450 ppm CO
2
equivalent in the 21st
century. Energy Econ. 31, S107
–
S120 (2009).
42. Rao, S. et al. IMAGE and MESSAGE Scenarios Limiting GHG Concentration to Low
Levels (IIASA Interim Report IR-08-020, International Institute for Applied
Systems Analysis, Laxenburg, Austria, 2008).
43. Taylor, K. E., Stouffer, R. J. & Meehl, G. A. A summary of the CMIP5 experimental
design. Æhttp://cmip-pcmdi.llnl.gov/cmip5/experiment_design.html?
submenuheader51æ(18 December 2009).
44. Randall, D. A. et al. in Climate Change 2007: The Physical Science Basis (eds
Solomon, S., Qin, D. & Manning, M.) 589
–
662 (Cambridge Univ. Press, 2007).
45. Cox, P. M. et al. Acceleration of global warming due to carbon-cycle feedbacks in a
coupled climate model. Nature 408, 184
–
187 (2000).
46. Friedlingstein, P. et al. Climate-carbon cycle feedback analysis: results from the
(CMIP)-M-4 model intercomparison. J. Clim. 19, 3337
–
3353 (2006).
47. van Vuuren, D. P. et al. Temperature increase of 21st century mitigation scenarios.
Proc. Natl Acad. Sci. USA 105, 15258
–
15262 (2008).
48. Clarke, L. et al. Scenarios of Greenhouse Gas Emissions and Atmospheric
Concentrations (Sub-report 2.1A of Synthesis and Assessment Product 2.1, US
Climate Change Science Program and the Subcommittee on Global Change
Research, Department of Energy, Office of Biological & Environmental Research,
Washington DC, 2007).
49. Fisher, B. S. et al. in Climate Change 2007: Mitigation (eds Metz, B., Davidson, O. R.,
Bosch, P. R., Dave, R. & Meyer, L. A.) 169
–
250 (Cambridge Univ. Press, 2007).
50. Weyant, J. et al. Report of 2.6 versus 2.9 Watts/m
2
RCP evaluation panel Æhttp://
www.ipcc.ch/meetings/session30/inf6.pdfæ(31 March 2009).
51. Lamarque, J.-F. et al. Gridded emissions in support of IPCC AR5. IGAC Newsl. 41,
12
–
18 (2009).
52. Meehl, G. A. et al. Decadal prediction: can it be skillful? Bull. Am. Meteorol. Soc. 90,
1467
–
1485 (2009).
53. Mitchell, T. D. Pattern scaling
–
an examination of the accuracy of the technique
for describing future climates. Clim. Change 60, 217
–
242 (2003).
54. Huntingford, C. & Cox, P. M. An analogue model to derive additional climate
change scenarios from existing GCM simulations. Clim. Dyn. 16, 575
–
586 (2000).
55. Rao, S. & Riahi, K. The role of non-CO
2
greenhouse gases in climate change
mitigation: Long-term scenarios for the 21st century. Multigas mitigation and
climate policy. Energy J. 3(Special Issue), 177
–
200 (2006).
56. Riahi, K., Gruebler, A. & Nakicenovic, N. Scenarios of long-term socio-economic
and environmental development under climate stabilization. Technol. Forecast.
Soc. Change 74, 887
–
935 (2007).
57. Fujino, J. et al. Multigas mitigation analysis on stabilization scenarios using AIM
global model. Multigas mitigation and climate policy. Energy J. 3(Special Issue),
343
–
354 (2006).
58. Hijioka, Y., Matsuoka, Y., Nishimoto, H., Masui, M. & Kainuma, M. Global GHG
emissions scenarios under GHG concentration stabilization targets. J. Glob.
Environ. Eng. 13, 97
–
108 (2008).
59. Smith, S. J. & Wigley, T. M. L. Multi-gas forcing stabilization with the MiniCAM.
Multigas mitigation and climate policy. Energy J. 3(Special Issue), 373
–
391
(2006).
60. van Vuuren, D. P., Eickhout, B., Lucas, P. L. & den Elzen, M. G. J. Long-term multi-
gas scenarios to stabilise radiative forcing — Exploring costs and benefits within
an integrated assessment framework. Multigas mitigation and climate policy.
Energy J. 3(Special Issue), 201
–
234 (2006).
61. van Vuuren, D. P. et al. Stabilizing greenhouse gas concentrations at low levels: an
assessment of reduction strategies and costs. Clim. Change 81, 119
–
159 (2007).
62. Manabe, S. & Wetherald, R. T. Thermal equilibrium of the atmosphere with a
given distribution of relative humidity. J. Atmos. Sci. 24, 241
–
259 (1967).
63. Manabe, S. et al. A global ocean-atmosphere climate model: Part I. The
atmospheric circulation. J. Phys. Oceanogr. 5, 3
–
29 (1975).
64. Arrhenius, S. On the influence of carbonic acid in the air upon the temperature of
the ground. Lond. Edinb. Dublin Phil. Mag. J. Sci. (5th ser.) 41, 237
–
275 (1896).
65. Keeling, C. D. The concentration and isotopic abundance of carbon dioxide in the
atmosphere. Tellus 12, 200
–
203 (1960).
66. Hansen, J. et al. Global climate changes as forecast by Goddard Institute for Space
Studies three-dimensional model. J. Geophys. Res. 93, 9341
–
9364 (1988).
67. WMO/UNEP/ICSU. Report of the Study Conference on Sensitivity of Ecosystems and
Society to Climate Change (WCP-83, UNESCO, Geneva, 1984).
68. WMO/UNEP/ICSU. Report of the International Conference on the Assessment of the
Role of Carbon Dioxide and of other Greenhouse Gases in Climate Variations and
Associated Impacts (WMO No. 661, UNESCO, Geneva, 1986).
69. Carter, T. R., Parry, M. L. & Porter, J. H. Climatic change and future agroclimatic
potential in Europe. Int. J. Climatol. 11, 251
–
269 (1991).
70. Carter, T. R., Parry, M. L., Harasawa, H. & Nishioka, S. (eds) IPCC Technical
Guidelines for Assessing Climate Change Impacts and Adaptations (Dept of
Geography, University College London, UK, and Center for Global Environmental
Research, National Institute for Environmental Studies, Tsukuba, Japan, 1994).
NATUREjVol 463j11 February 2010 PERSPECTIVES
755
Macmillan Publishers Limited. All rights reserved
©2010
71. Hulme, M., Raper, S. C. B. & Wigley, T. M. L. An integrated framework to address
climate change (ESCAPE) and further developments of the global and regional
climate modules (MAGICC). Energy Policy 23, 347
–
355 (1995).
72. Melillo, J. M. et al. Vegetation/Ecosystem Modeling and Analysis Project
(VEMAP): comparing biogeography and biogeochemistry models in a
continental-scale study of terrestrial ecosystem responses to climate change and
CO
2
doubling. Glob. Biogeochem. Cycles 9, 407
–
437 (1995).
73. Smith, J. B., et al. Vulnerability and Adaptation to Climate Change. Interim Results
from the U.S. Country Studies Program (Kluwer Academic, 1996).
74. Nakic
´enovic
´, N., Victor, N. & Morita, T. Emissions scenarios database and review
of scenarios. Mitig. Adapt. Strategies Glob. Change 3, 95
–
120 (1998).
75. Watson, R. T., Zinyowera, M. C. & Moss, R. H. (eds) The Regional Impacts of
Climate Change: An Assessment of Vulnerability (Cambridge Univ. Press, 1998).
76. Carter, T. R. et al. Climate Change in the 21st Century
–
Interim Characterizations
Based on the New IPCC Emissions Scenarios (The Finnish Environment 433, Finnish
Environment Institute, Helsinki, 2000).
77. Morita, T. et al. in Climate Change 2001: Mitigation (eds Metz, B., Davidson, O.,
Swart, R. & Pan J.) 115
–
166 (Cambridge Univ. Press, 2007).
78. United Kingdom Climate Impacts Programme. Socio-economic Scenarios for
Climate Change Impact Assessment: A Guide to Their Use in the UK Climate Impacts
Programme (United Kingdom Climate Impacts Programme, Oxford, 2001).
79. Ruosteenoja, K., Carter, T. R., Jylha
¨, K. & Tuomenvirta, H. Future Climate in World
Regions: An Intercomparison of Model-based Projections for the New IPCC Emissions
Scenarios (The Finnish Environment 644, Finnish Environment Institute, Helsinki,
2003).
80. Weyant, J. P., De La Chesnaye, C. F. & Blenford, J. Overview of EMF21: multi-
greenhouse gas mitigation and climate policy. Energy J. 27 (Special Issue), 1
–
33
(2006).
81. Murphy, J. M. et al. UK Climate Projections Science Report: Climate Change
Projections (Met Office Hadley Centre, Exeter, UK, 2009).
82. van der Linden, P. & Mitchell, J. F. B. (eds) ENSEMBLES: Climate Change and its
Impacts: Summary of research and results from the ENSEMBLES project (Met Office
Hadley Centre, Exeter, UK, 2009).
83. U.S. Climate Change Science Program. Strategic Plan for the Climate Change
Science Program, Final Report (eds Subcommittee on Global Change Research)
Figure 2.5 19 (US Climate Change Science Program, Washington DC, 2003).
84. Le Treut, H. et al. in Climate Change 2007: The Physical Science Basis (eds Solomon,
S. et al.) 93
–
127 (Cambridge Univ. Press, 2007).
85. Ahmad, Q. K. et al. in Climate Change 2001: Impacts, Adaptation and Vulnerability
(eds McCarthy, J. J., Canziani, O. F., Leary, N. A., Dokken, D. J. & White, K. S.)
105
–
143 (Cambridge Univ. Press, 2001).
86. US Department of Energy. Science Challenges and Future Directions: Climate Change
Integrated Assessment Research (Report of the Workshop on Integrated
Assessment, November 2008, US Department of Energy, Office of Science,
Washington DC, 2009).
87. van Vuuren, D. P. & Riahi, K. Do recent emission trends imply higher emissions
forever? Clim. Change 91, 237
–
248 (2008).
Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements The authors acknowledge the following individuals for their
contributions: L. Arris, M. Babiker, F. Birol, P. Bosch, O. Boucher, S. Brinkman,
E. Calvo, I. Elgizouli, L. Erda, J. Feddema, A. Garg, A. Gaye, M. Ibarraran, E. La
Rovere, B. Metz, R. Jones, J. Kelleher, J. F. Lamarque, B. Matthews, L. Meyer, B.
O’Neill, S. Nishioka, R. Pichs, H. Pitcher, P. Runci, D. Shindell, P. R. Shukla,
A. Snidvongs, P. Thornton, J. P. van Ypersele, V. Vilarin
˜o and M. Zurek.
Author Contributions R.H.M. is coordinating lead author of the paper. J.A.E.,
K.A.H., M.R.M., S.K.R. and D.P.v.V. are principal co-authors of the paper. All others
are co-authors. Authors are drawn from the integrated assessment modelling and
climate modelling communities, and from the impacts, adaptation and vulnerability
research communities; all contributed important inputs to the process.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial interests.
Correspondence and requests for materials should be addressed to R.H.M.
(rhm@pnl.gov).
PERSPECTIVES NATUREjVol 463j11 February 2010
756
Macmillan Publishers Limited. All rights reserved
©2010
