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

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 degrees C ( Southern Hemisphere), 0.4 degrees C globally, 0.6 degrees C ( Northern Hemisphere), 1.5 - 3 degrees C ( wintertime Arctic), and 1.5 - 2 degrees C ( similar to 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 similar to 1 W/m(2); over east Asia it exceeds 5 W/ m 2. 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.