6. Non-CO2 forcings
If fossil fuel CO2 emissions continue to increase unabated, other
climate forcings are relatively unimportant. However, this scenario is
unlikely. Global warming is becoming apparent. Efforts to slow GHG
emissions and stabilize global climate may increase. In this case,
especially if the warming that constitutes 'danger' to the planet is
as small as we estimate, non-CO2 forcings become very important.
Indeed, because some further increase of CO2 is inevitable, it is
probably implausible to keep additional global warming less than 1�C,
unless non-CO2 forcings are addressed aggressively.
Figure 8 summarizes known global climate forcings. Units are
effective forcing in Wm-2 in 2000 relative to pre-industrial times.
Well-established indirect effects are grouped with the primary
forcing. The bases for these estimates are given by Hansen et al.