Aerosol contribution to the rapid warming of 1 near - term climate under RCP 2 . 6

The importance of aerosol emissions for near term climate projections is 3 investigated by analysing simulations with the HadGEM2-ES model under 4 two different emissions scenarios: RCP2.6 and RCP4.5. It is shown that the 5 near term warming projected under RCP2.6 is greater than under RCP4.5, 6 even though the greenhouse gas forcing is lower. Rapid and substantial re-7 ductions in sulphate aerosol emissions due to a reduction of coal burning in 8 RCP2.6 lead to a reduction in the negative shortwave forcing due to aerosol 9 direct and indirect effects. Indirect effects play an important role over the 10 northern hemisphere oceans, especially the subtropical northeastern Pacific 11 where an anomaly of 5-10 Wm −2 develops. The pattern of surface temper-12 ature change is consistent with the expected response to this surface radi-13 ation anomaly, whilst also exhibiting features that reflect redistribution of 14 energy, and feedbacks, within the climate system. These results demonstrate 15 the importance of aerosol emissions as a key source of uncertainty in near 16 term projections of global and regional climate.