What are Emissions Scenarios?
In order to determine the impact of climate change in the future, we need to have an idea of the concentrations of greenhouse gases and other pollutants in the atmosphere to which climate is sensitive, in the years to come. These concentrations depend on their emissions from various sources, natural as well as man-made.
Emissions scenarios describe future releases into the atmosphere of greenhouse gases, aerosols, and other pollutants and, along with information on land use and land cover, provide inputs to climate models. They are based on assumptions about driving forces such as patterns of economic and population growth, technology development, and other factors. Levels of future emissions are highly uncertain, and so scenarios provide alternative images of how the future might unfold. They provide an appropriate tool with which to analyse how driving forces may influence future emission outcomes and to assess the associated uncertainties. They assist in climate change analysis, including climate modelling and the assessment of impacts, adaptation, and mitigation. The possibility that any single emissions path will occur as described in scenarios is highly uncertain.
The following emissions scenarios have been used by researchers and other analysts to project future climate change and develop mitigation strategies.
Background to Emissions Scenarios
A set of scenarios was developed to represent the range of driving forces and emissions in the scenario literature so as to reflect current understanding and knowledge about underlying uncertainties. They exclude only outlying “surprise” or “disaster” scenarios in the literature.
Any scenario necessarily includes subjective elements and is open to various interpretations. No judgment is offered by the IPCC as to the preference for any of the scenarios and they are not assigned probabilities of occurrence, neither should they be interpreted as policy recommendations. The Special Report on Emissions Scenarios (SRES), published by the IPCC in 2000, describes the emissions scenarios that have been used to make projections of possible future climate change, for the IPCC Third Assessment Report (TAR), published in 2001, and in the IPCC Fourth Assessment Report (AR4), published in 2007. The projected CO2 emissions for these scenarios are shown below.
Carbon emissions for four emission scenarios (Image: IPCC)
The SRES Scenarios
There are 40 different scenarios, each making different assumptions for future greenhouse gas pollution, land-use and other driving forces. These emissions scenarios are organized into families, which contain scenarios that are similar to each other in some respects. The following are the major families of SRES emissions scenarios:
[Further information] about how these Scenarios are used can be found in the climate projections webpage.
[Technical information] on SRES can be found in the IPCC’s special report on emission scenarios
Representative Concentration Pathways
The Representative Concentration Pathways (RCP) are based on selected scenarios from four modelling teams/models working on integrated assessment modelling, climate modelling, and modelling and analysis of impacts. The RCPs are not new, fully integrated scenarios (i.e., they are not a complete package of socioeconomic, emissions, and climate projections). They are consistent sets of projections of only the components of radiative forcing (the change in the balance between incoming and outgoing radiation to the atmosphere caused primarily by changes in atmospheric composition) that are meant to serve as input for climate modelling. Conceptually, the process begins with pathways of radiative forcing, not detailed socioeconomic narratives or scenarios. Central to the process is the concept that any single radiative forcing pathway can result from a diverse range of socioeconomic and technological development scenarios. Four RCPs were selected, defined and named according to their total radiative forcing in 2100 (see table below). Climate modellers will conduct new climate model experiments using the time series of emissions and concentrations associated with the four RCPs, as part of the preparatory phase for the development of new scenarios for the IPCC's Fifth Assessment Report (expected to be completed in 2014) and beyond.
Table 1.1: Overview of Representative Concentration Pathways (RCPs)
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