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Emissions scenarios

Greenhouse gas emissions contribute to the warming of the earth's atmosphere and affect how the climate might change in the future. It is impossible to predict exactly how much greenhouse gas emissions will be released in the future. In light of this climate projections are given for a number of different plausible scenarios for greenhouse gas emissions.

These scenarios are based on a set of assumptions about factors such as socio-economic development and technological change. The emissions scenarios used in UKCP09 were developed by the Intergovernmental Panel on Climate Change (IPCC).

Three emissions scenarios are used in UKCP09:

1. Low emissions (also known as B1);

2. Medium emissions (also known as A1B); and

3. High emissions (also known as A1FI).

UKCP09 treats these scenarios as equally plausible. When presenting UKCP09 projections you may want to present findings for a range of scenarios to show the range of possible outcomes.

In detail

Modelling of future climate change requires estimation of future levels of emissions of greenhouse gases and other substances such as aerosols and aerosol precursors. Future emissions are the product of complex dynamic systems, determined by factors such as population change, socio-economic development, and technological advances. Uncertainty about future emissions is one source of uncertainty associated with the modelling of future climate change.

In the IPCC Special Report on Emissions Scenarios (SRES) (Nakićenović et al. 2000), new emissions scenarios - the so-called SRES scenarios - were published.

In UKCP09, projections are developed under three different emissions scenarios, two of which come from the A1 'storyline', and one from the B1 'storyline' developed by the IPCC Special Report on Emissions Scenarios. Within UKCP09 the emission scenarios are labelled based on their relative greenhouse gas emissions levels - High (SRES A1FI), Medium (SRES A1B) and Low (SRES B1) - and comprise a wide range but not the full set of SRES emissions scenarios. 

An emissions scenario is one of the elements required when building a request in the UKCP09 User Interface.

The implications of user choices are discussed in section 4.4 of the Climate change projections report.

More information about the emissions scenarios that were used in the preparation of the UKCP09 projections is given in Section 3.2.13 and Annex 1 of the UKCP09 Climate change projections report. Further details about the uncertainties associated with emissions scenarios are provided in secton 2.4 of the UKCP09 Climate change projections report.

One of the advances in UKCP09 is that realisations of time-dependent climate changes for the 21st century were obtained for all three emissions scenarios reported (A1B, B1 and A1FI), making the final results more robust than those presented in previous UK climate scenarios. However, constraints associated with the experimental design mean that the results for B1 and A1FI are considered less robust than those for A1B.

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