Figure 19-1: Global mean
temperature change (from 1990) as a function of CO2 concentration for
SRES scenarios. For any given CO2 level, uncertainties in temperature
arise through several factors. The three most important are accounted for here:
First, different temperatures for a given future CO2 level may arise
because each emissions scenario has different levels of other GHGs and different
levels of SO2 emissions—factors that lead to a range of possible
non-CO2 forcings (results here consider all six SRES illustrative scenarios);
second, different temperatures arise because of uncertainties in climate sensitivity
(three values—1.5, 2.5, and 4.5ºC equilibrium warming for a CO2
doubling—are used here); and third, different temperatures arise because
different rates of radiative forcing change and different climate sensitivities
lead to different levels of damping of the instantaneous equilibrium response.
