Ratio of aerosol-induced to total simulated near-surface air temperature change in each RCP scenario between 2005 and 2035
Figure 3. Ratio of aerosol-induced to total simulated near-surface air temperature change in each RCP scenario between 2005 and 2035. Aerosol-induced temperature changes are inferred from the difference between mean temperature changes in the RCP scenario simulations between 2031–2040 and 2001–2010 and mean temperature changes in the corresponding GHG-only simulations between the same periods. The inferred aerosol response therefore also includes the response to land-use, solar irradiance and ozone changes over this period, but responses to these forcings are expected to be relatively small. Hatching indicates where the ensemble mean aerosol response is not significant at the 10% level.
The representative concentration pathway (RCP) scenarios all assume stringent emissions controls on aerosols and their precursors, and hence include progressive decreases in aerosol and aerosol precursor emissions through the 21st century. Recent studies have suggested that the resultant decrease in aerosols could drive rapid near-term warming, which could dominate the effects of greenhouse gas (GHG) increases in the coming decades. In CanESM2 simulations, we find that under the RCP 2.6 scenario, which includes the fastest decrease in aerosol and aerosol precursor emissions, the contribution of aerosol reductions to warming between 2000 and 2040 is around 30%. Moreover, the rate of warming in the RCP 2.6 simulations declines gradually from its present-day value as GHG emissions decrease. Thus, while aerosol emission reductions contribute to gradual warming through the 21st century, we find no evidence that aerosol emission reductions drive particularly rapid near-term warming in this scenario. In the near-term, as in the long-term, GHG increases are the dominant driver of warming.