A plausible representation of the future development of emissions of substances (e.g. greenhouse gases and aerosols that can influence global climate. These representations are based on a coherent and internally consistent set of assumptions about determining factors (such as demographic and socio-economic development, technological change) and their key relationships. The emissions scenarios used in UKCP09 do not include the effects of planned mitigation policies, but do assume different pathways of technological and economic growth which include a switch from fossil fuels to renewable sources of energy.
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 () (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 UKCP09 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 of the UKCP09 Climate change projections report and in Annex 1. Further details about the uncertainties associated with emissions scenarios are provided in Section 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 ( A1B1, B1 and A1FI), making the final results more robust than those presented in previous UK climate scenarios. However, constraints associated with the experimental design (such as that the discrepancy term for future projected variables was assumed to be the same for all three emissions scenarios as obtained using A1B1) mean that the results for B1 and A1FI are considered less robust than those for A1B1.
It should be remembered that different UKCP09 use one or more of these emissions scenarios. In addition, a has been developed to explore a high-end, very unlikely, scenario for sea level rise.