Figure 5: The global climate
of the 21st century will depend on natural changes and the response of the climate
system to human activities.
Climate models project the response of many climate variables – such as increases
in global surface temperature and sea level – to various scenarios of greenhouse
gas and other human-related emissions. (a) shows the CO2 emissions
of the six illustrative SRES scenarios, which are summarised in the box on page
18, along with IS92a for comparison purposes with the SAR. (b) shows projected
CO2 concentrations. (c) shows anthropogenic SO2 emissions.
Emissions of other gases and other aerosols were included in the model but are
not shown in the figure. (d) and (e) show the projected temperature and sea level
responses, respectively. The “several models all SRES envelope” in (d)
and (e) shows the temperature and sea level rise, respectively, for the simple
model when tuned to a number of complex models with a range of climate sensitivities.
All SRES envelopes refer to the full range of 35 SRES scenarios. The “model
average all SRES envelope” shows the average from these models for the range
of scenarios. Note that the warming and sea level rise from these emissions would
continue well beyond 2100. Also note that this range does not allow for uncertainty
relating to ice dynamical changes in the West Antarctic ice sheet, nor does it
account for uncertainties in projecting non-sulphate aerosols and greenhouse gas
concentrations. [Based upon (a) Chapter 3, Figure
3.12, (b) Chapter 3, Figure
3.12, (c) Chapter 5, Figure
5.13, (d) Chapter 9, Figure
9.14, (e) Chapter 11, Figure
11.12, Appendix II
