Figure 12.13: Global mean
temperature in the decade 2036 to 2046 (relative to pre-industrial, in response
to greenhouse gas and sulphate aerosol forcing following the IS92a (IPCC, 1992)
scenario), based on original model simulations (squares) and after scaling to
fit the observed signal as in Figure 12.12(a) (diamonds),
with 5 to 95% confidence intervals. While the original projections vary (depending,
for example, on each model�s climate sensitivity), the scale should be independent
of errors in both sensitivity and rate of oceanic heat uptake, provided these
errors are persistent over time. GS indicates combined greenhouse and sulphate
forcing. G shows the impact of setting the sulphate forcing to zero but correcting
the response to be consistent with observed 20th century climate change. G&S
indicates greenhouse and sulphate responses estimated separately (in which case
the result is also approximately independent, under this forcing scenario, to
persistent errors in the sulphate forcing and response) and G&S&N indicates
greenhouse, sulphate and natural responses estimated separately (showing the small
impact of natural forcing on the diagnostic used for this analysis). (From Allen
et al., 2000b.)
