Special Report on Emissions Scenarios

Special Report on Emissions Scenarios

Ask a question about 'Special Report on Emissions Scenarios'
Start a new discussion about 'Special Report on Emissions Scenarios'
Answer questions from other users
Full Discussion Forum
The Special Report on Emissions Scenarios (SRES) was prepared by the Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 (IPCC) in 2000, based on data developed at the Earth Institute at Columbia University
Columbia University
Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...

. The emissions scenarios
Climate change scenario
This article is about climate change scenarios. Socioeconomic scenarios are used by analysts to make projections of future greenhouse gas emissions and to assess future vulnerability to climate change...

 described in the Report have been used to make projections of possible future climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

. The SRES scenarios, as they are often called, were used in the IPCC Third Assessment Report
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 (TAR), published in 2001, and in the IPCC Fourth Assessment Report
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

 (AR4), published in 2007.

The SRES scenarios were designed to improve upon some aspects of the IS92 scenarios, which had been used in the earlier IPCC Second Assessment Report
IPCC Second Assessment Report
The Second Assessment Report of the Intergovernmental Panel on Climate Change , published in 1996, is an assessment of the then available scientific and socio-economic information on climate change...

 of 1995. At the time they were developed, the range of global emissions projected across all forty of the SRES scenarios covered the 5th to 95th percentile range of the emission scenarios literature.


The four SRES scenario families of the Fourth Assessment Report vs. projected global average surface warming until 2100
(Summary; PDF)

More economic focus

More environmental focus
(homogeneous world)
rapid economic growth
(groups: A1T; A1B; A1Fl)
1.4 - 6.4 °C
global environmental sustainability 
1.1 - 2.9 °C
Regionalization is the tendency to form regions, or the process of doing so.Regionalization can be observed in various disciplines:*In geography, it has two ways: the process of delineating the Earth, its small areas or other units into regions and a state of such a delineation.*In globalization...

(heterogeneous world)
regionally oriented
economic development

2.0 - 5.4 °C
local environmental sustainability
1.4 - 3.8 °C

Because projections of climate change depend heavily upon future human activity, climate models are run against scenarios. There are 40 different scenarios, each making different assumptions for future greenhouse gas pollution, land-use and other driving forces. Assumptions about future technological development as well as the future economic development are thus made for each scenario. Most include an increase in the consumption of fossil fuels; some versions of B1 have lower levels of consumption by 2100 than in 1990 http://www.grida.no/climate/ipcc_tar/wg1/figspm-5.htm. Overall global GDP will grow by a factor of between 5-25 in the emissions scenarios.

These emissions scenarios are organized into families, which contain scenarios that are similar to each other in some respects. IPCC assessment report projections for the future are often made in the context of a specific scenario family.

Scenario families

Scenario families contain individual scenarios with common themes. The six families of scenarios discussed in the IPCC's Third Assessment Report
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 (TAR) and Fourth Assessment Report
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

 (AR4) are A1FI, A1B, A1T, A2, B1, and B2.

Scenario descriptions are based on those in AR4, which are identical to those in TAR.


The A1 scenarios are of a more integrated world. The A1 family of scenarios is characterized by:
  • Rapid economic growth.
  • A global population that reaches 9 billion in 2050 and then gradually declines.
  • The quick spread of new and efficient technologies.
  • A convergent world - income and way of life converge between regions. Extensive social and cultural interactions worldwide.

There are subsets to the A1 family based on their technological emphasis:
  • A1FI - An emphasis on fossil-fuels (Fossil Intensive).
  • A1B - A balanced emphasis on all energy sources.
  • A1T - Emphasis on non-fossil energy sources.


The A2 scenarios are of a more divided world. The A2 family of scenarios is characterized by:
  • A world of independently operating, self-reliant nations.
  • Continuously increasing population.
  • Regionally oriented economic development.
  • Slower and more fragmented technological changes and improvements to per capita income.


The B1 scenarios are of a world more integrated, and more ecologically friendly. The B1 scenarios are characterized by:
  • Rapid economic growth as in A1, but with rapid changes towards a service and information economy.
  • Population rising to 9 billion in 2050 and then declining as in A1.
  • Reductions in material intensity and the introduction of clean and resource efficient technologies.
  • An emphasis on global solutions to economic, social and environmental stability.


The B2 scenarios are of a world more divided, but more ecologically friendly. The B2 scenarios are characterized by:
  • Continuously increasing population, but at a slower rate than in A2.
  • Emphasis on local rather than global solutions to economic, social and environmental stability.
  • Intermediate levels of economic development.
  • Less rapid and more fragmented technological change than in A1 and B1.

SRES scenarios and climate change initiatives

While some scenarios assume a more environmentally friendly world than others, none include any climate-specific initiatives, such as the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...



The SRES scenarios were criticised by Ian Castles
Ian Castles
Ian Castles, AO OBE was Secretary of the Australian Government Department of Finance , the Australian Statistician , and a Visiting Fellow at the Asia Pacific School of Economics and Government at the Australian National University, Canberra.Castles was born in Kyneton, Victoria and educated at...

, and David Henderson
David Henderson (economist)
David Henderson is an economist. He was the Head of the Economics and Statistics Department at the OECD in 1984–1992. Before that he worked as an academic economist in Britain, first at Oxford and later at University College London ; as a British civil servant David Henderson (born 1927)...

. The core of their critique was the use of market exchange rates (MER) for international comparison, in lieu of the theoretically favoured PPP exchange rate
Geary-Khamis dollar
The Geary-Khamis dollar, more commonly known as the international dollar, is a hypothetical unit of currency that has the same purchasing power that the U.S. dollar had in the United States at a given point in time. It is widely used in economics. The years 1990 or 2000 are often used as a...

 which corrects for differences in purchasing power. The IPCC rebutted this criticism

The positions in the debate can be summarised as follows. Using MER, the SRES scenarios overstate income differences in past and present, and overestimate future economic growth in developing countries. This, Castles and Henderson argue, leads to an overestimate of future greenhouse gas emissions. The IPCC would have made climate change more dramatic than it is.

However, the difference in economic growth is offset by a difference in energy intensity. Some say these two opposite effects fully cancel, some say this is only partial. Overall, the effect of a switch from MER to PPP is likely to have a minimal effect on carbon dioxide concentrations in the atmosphere.

But even if global climate change is not affected, it has been argued that the regional distribution of emissions and incomes is very different between an MER and a PPP scenario. This would influence the political debate: In a PPP scenario, China and India have a much smaller share of global emissions. It would also affect vulnerability to climate change: in a PPP scenario, poor countries grow slower and would face greater impacts.

Availability of fossil fuels

As part of the SRES, IPCC authors assessed the potential future availability of fossil fuels for energy use. The issue of whether or not the future availability of fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s would limit future carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 emissions was considered in the Third Assessment Report; it concluded that limits on fossil fuel resources would not limit carbon emissions in the 21st century. Their estimate for conventional coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 reserves was around 1,000 gigatonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s of carbon (GtC), with an upper estimate of between 3,500 and 4,000 GtC. This compares with cumulative carbon emissions up to the year 2100 of about 1,000 GtC for the SRES B1 scenario, and about 2,000 GtC for the SRES A1FI scenario.

The carbon in proven conventional oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

 and gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 reserves was estimated to be much less than the cumulative carbon emissions associated with atmospheric stabilization of CO2 concentrations at levels of 450 ppmv or higher. The Third Assessment Report suggested that the future makeup of the world's energy mix would determine whether or not greenhouse gas concentrations were stabilized in the 21st century. The future energy mix might be based more on the exploitation of unconventional oil and gas (e.g., tar sands
Tar sands
Bituminous sands, colloquially known as oil sands or tar sands, are a type of unconventional petroleum deposit. The sands contain naturally occurring mixtures of sand, clay, water, and a dense and extremely viscous form of petroleum technically referred to as bitumen...

, shale oil
Shale oil
Shale oil, known also as kerogen oil or oil-shale oil, is an unconventional oil produced from oil shale by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock into synthetic oil and gas...

, shale gas
Shale gas
Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...

), or more on the use of non-fossil energy sources, like renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...



Hook et al. (2009, abstract) criticized the SRES scenarios for being biased towards “exaggerated resource availability” and making “unrealistic expectations on future production outputs from fossil fuels.” Patzek and Croft (2010, p. 3113) made a prediction of future coal production and carbon emissions. In their assessment, all but the lowest emission SRES scenarios projected far too high levels of future coal production and carbon emissions (Patzek and Croft, 2010, pp. 3113–3114). In a discussion paper, Aleklett (2007, p. 17) viewed SRES projections between the years 2020 and 2100 as “absolutely unrealistic”. In Aleklett's analysis, emissions from oil and gas were lower than all of the SRES projections, with emissions from coal much lower than the majority of SRES projections (Aleklett, 2007, p. 2).

Select Committee report

In 2005, the UK Parliament's House of Lords
House of Lords
The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

 Economics Affairs Select Committee produced a report on the economics of climate change. As part of their inquiry, they took evidence on criticisms of the SRES. Among those who gave evidence to the Committee were Dr Ian Castles, a critic of the SRES scenarios, and Prof Nebojsa Nakicenovic, who co-edited the SRES. IPCC author Dr Chris Hope commented on the SRES A2 scenario, which is one of the higher emissions scenarios of the SRES. Hope assessed and compared the marginal damages of climate change using two versions of the A2 scenario. In one version of the A2 scenario, emissions were as the IPCC projected. In the other version of A2, Hope reduced the IPCC's projected emissions by a half (i.e., 50% of the original A2 scenario). In his integrated assessment model
Integrated assessment modelling
Integrated assessment modelling is a type of scientific modelling that is increasingly common in the environmental sciences and environmental policy analysis. The modelling is integrated because environmental problems do not respect the borders between academic disciplines. Integrated assessment...

, both of these versions of the A2 scenario lead to almost identical estimates of marginal climate damages (the present-day value of emitting one tonne of CO2 into the atmosphere). Based on this finding, Hope argued that present day climate policy was insensitive to whether or not you accepted the validity of the higher emission SRES scenarios.

IPCC author Prof Richard Tol
Richard Tol
Richard S. J. Tol is a Research Professor at the Economic and Social Research Institute, Dublin, Ireland, where he works in the research areas of energy economics and environmental economics...

 commented on the strengths and weaknesses of the SRES scenarios. In his view, the A2 SRES marker scenario was, by far, the most realistic. UK Government departments Defra and HM Treasury
HM Treasury
HM Treasury, in full Her Majesty's Treasury, informally The Treasury, is the United Kingdom government department responsible for developing and executing the British government's public finance policy and economic policy...

 argued that case for action on climate change was not undermined by the Castles and Henderson critique of the SRES scenarios. They also commented that unless effective action was taken to curb emissions growth, other bodies, like the International Energy Agency
International Energy Agency
The International Energy Agency is a Paris-based autonomous intergovernmental organization established in the framework of the Organisation for Economic Co-operation and Development in 1974 in the wake of the 1973 oil crisis...

, expected greenhouse gas emissions to continue to rise into the future.

Comparison with a “no policy” scenario

In a report published by the MIT Joint Program on the Science and Policy of Global Change, Webster et al. (2008) compared the SRES scenarios with their own “no policy” scenario. Their no-policy scenario assumes that in the future, the world does nothing to limit greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

 emissions. They found that most of the SRES scenarios were outside of the 90% probability range of their no-policy scenario (Webster et al., 2008, p. 1). Most of the SRES scenarios were consistent with efforts to stabilize greenhouse gas concentrations in the atmosphere. Webster et al. (2008, p. 54) noted that the SRES scenarios were designed to cover most of the range of future emission levels in the published scientific literature
Scientific literature
Scientific literature comprises scientific publications that report original empirical and theoretical work in the natural and social sciences, and within a scientific field is often abbreviated as the literature. Academic publishing is the process of placing the results of one's research into the...

. Many such scenarios in the literature presumably assumed that future efforts would be made to stabilize greenhouse gas concentrations.

Observed emissions rates

Between the 1990s and 2000s, the growth rate in CO2 emissions from fossil fuel burning and industrial processes increased (McMullen and Jabbour, 2009, p. 8). The growth rate from 1990-1999 averaged 1.1% per year. This increased to an average of 3.5% per year for the time period 2000-2007. The emissions growth rate since 2000 was greater than that projected in the most fossil-fuel intensive SRES A1FI emissions scenario (McMullen and Jabbour, 2009, p. 8; Raupach et al., 2007, fig.1).

Human-caused greenhouse gas emissions set a record in 2010, a 6% jump on 2009 emissions, exceeding even the worst case scenario cited in the IPCC Fourth Assessment Report
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...


Post-SRES projections

As part of the IPCC Fourth Assessment Report, the literature on emissions scenarios was assessed. Baseline emissions scenarios published since the SRES were found to be comparable in range to those in the SRES. IPCC (2007) noted that post-SRES scenarios had used lower values for some drivers for emissions, notably population projection
Population projection
Population projection, in the field of demography, is an estimate of a future population. In contrast with intercensal estimates and censuses, which usually involve some sort of field data gathering, projections usually involve mathematical models based only on pre-existing data. A projection may...

s. However, of the assessed studies that had incorporated new population projections, changes in other drivers, such as economic growth
Economic growth
In economics, economic growth is defined as the increasing capacity of the economy to satisfy the wants of goods and services of the members of society. Economic growth is enabled by increases in productivity, which lowers the inputs for a given amount of output. Lowered costs increase demand...

, resulted in little change in overall emission levels.

Individual studies

In the reference scenario of World Energy Outlook
World Energy Outlook
The annual World Energy Outlook is the International Energy Agency's flagship publication and it is widely recognised as the most authoritative energy source for global energy projections and analysis. It represents the leading source for medium to long-term energy market projections, extensive...

(IEA, 2004, p. 74), the International Energy Agency projected future energy-related CO2 emissions. Emissions were projected to increase by 62% between the years 2002 and 2030. This lies between the SRES A1 and B2 scenario estimates of +101% and +55%, respectively (Sims et al., 2007). As part of the IPCC Fourth Assessment Report, Sims et al. (2007) compared several baseline and mitigation scenarios
Climate change mitigation scenarios
Climate change mitigation scenarios are possible futures in which global warming is reduced by deliberate actions, such as a comprehensive switch to energy sources other than fossil fuels...

 out to the year 2030. The baseline scenarios included the reference scenario of IEA's World Energy Outlook 2006 (WEO 2006), SRES A1, SRES B2, and the ABARE reference scenario. Mitigation scenarios included the WEO 2006 Alternative policy, ABARE Global Technology and ABARE Global Technology + CCS
Carbon capture and storage
Carbon capture and storage , alternatively referred to as carbon capture and sequestration, is a technology to prevent large quantities of from being released into the atmosphere from the use of fossil fuel in power generation and other industries. It is often regarded as a means of mitigating...

. Projected total energy-related emissions in 2030 (measured in GtCO2-eq) were 40.4 for the IEA WEO 2006 reference scenario, 58.3 for the ABARE reference scenario, 52.6 for the SRES A1 scenario, and 37.5 for the SRES B2 scenario. Emissions for the mitigation scenarios were 34.1 for the IEA WEO 2006 Alternative Policy scenario, 51.7 for the ABARE Global Technology scenario, and 49.5 for the ABARE Global Technology + CCS scenario.

Garnaut et al. (2008, p. 392) made a projection of fossil-fuel CO2 emissions for the time period 2005-2030. Their “business-as usual” annual projected growth rate was 3.1% for this period. This compares to 2.5% for the fossil-fuel intensive SRES A1FI emissions scenario, 2.0% for the SRES median
In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...

 scenario (defined by Garnaut et al. (2008) as the median for each variable and each decade of the four SRES marker scenarios), and 1.6% for the SRES B1 scenario. Garnaut et al. (2008) also referred to projections over the same time period of the: US Climate Change Science Program (2.7% max, and 2.0% mean), International Monetary Fund
International Monetary Fund
The International Monetary Fund is an organization of 187 countries, working to foster global monetary cooperation, secure financial stability, facilitate international trade, promote high employment and sustainable economic growth, and reduce poverty around the world...

's 2007 World Economic Outlook
World Economic Outlook
World Economic Outlook is basically a survey conducted and published by International Monetary Fund. It is published twice and partly updated 3 times in an year. It portrays the world economy in the near and medium context...

(2.5%), Energy Modelling Forum (2.4% max, 1.7% mean), US Energy Information Administration
Energy Information Administration
The U.S. Energy Information Administration is the statistical and analytical agency within the U.S. Department of Energy. EIA collects, analyzes, and disseminates independent and impartial energy information to promote sound policymaking, efficient markets, and public understanding of energy and...

 (2.2% high, 1.8% medium, and 1.4% low), IEA's World Energy Outlook 2007 (2.1% high, 1.8 base case), and the base case from the Nordhaus model (1.3%).

As has already be stated in the section on fossil fuel availability, several authors have made emissions projections lower than those of the SRES scenarios.

External links