Fig. 2.

Target CO₂ emissions and concentrations under four CC carbonaceous aerosol emission scenarios using our “best estimate” of RF from carbonaceous aerosols of 0.22 W m^-2, as calculated using our simple atmospheric and economic model. (A) shows CO₂ emissions relative to 2005 levels (on the left axis) and as an annual emission rate (on the right axis). The solid lines in (B) show the associated CO₂ concentrations. The dashed lines in (B) indicate (on the left axis) total RF from all GHGs and carbonaceous aerosols in terms of ppm CO₂e and (on the right axis) the associated equilibrium warming assuming a 3 °C/CO₂ doubling climate sensitivity (24). The arrow (in A) indicates the 8 years difference in timing of the 50% reduction in CO₂ emissions between the full mitigation and constant emissions scenarios. The scenarios are: Full mitigation—complete elimination of emissions of carbonaceous aerosols from CC by 2100; and constant emissions—1996 carbonaceous aerosol emissions continue through 2100. “A2” and “B1” are high and low projections of carbonaceous aerosol emissions from ref. 23 based on IPCC SRES storylines.