Strong sensitivity of late 21st century climate to projected changes in short‐lived air pollutants

Abstract

This study examines the impact of projected changes (A1B “marker” scenario) in emissions of four short‐lived air pollutants (ozone, black carbon, organic carbon, and sulfate) on future climate. Through year 2030, simulated climate is only weakly dependent on the projected levels of short‐lived air pollutants, primarily the result of a near cancellation of their global net radiative forcing. However, by year 2100, the projected decrease in sulfate aerosol (driven by a 65% reduction in global sulfur dioxide emissions) and the projected increase in black carbon aerosol (driven by a 100% increase in its global emissions) contribute a significant portion of the simulated A1B surface air warming relative to the year 2000: 0.2°C (Southern Hemisphere), 0.4°C globally, 0.6°C (Northern Hemisphere), 1.5–3°C (wintertime Arctic), and 1.5–2°C (∼40% of the total) in the summertime United States. These projected changes are also responsible for a significant decrease in central United States late summer root zone soil water and precipitation. By year 2100, changes in short‐lived air pollutants produce a global average increase in radiative forcing of ∼1 W/m2; over east Asia it exceeds 5 W/m2. However, the resulting regional patterns of surface temperature warming do not follow the regional patterns of changes in short‐lived species emissions, tropospheric loadings, or radiative forcing (global pattern correlation coefficient of −0.172). Rather, the regional patterns of warming from short‐lived species are similar to the patterns for well‐mixed greenhouse gases (global pattern correlation coefficient of 0.8) with the strongest warming occurring over the summer continental United States, Mediterranean Sea, and southern Europe and over the winter Arctic.