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Abstract

On the basis of historical simulations of the atmospheric distribution of sulfate aerosol over Europe, we have estimated the evolution of the direct shortwave radiative forcing due to sulfate aerosol from 1900 to the present day. Following the trend of atmospheric sulfate burden, the radiative forcing reaches its peak in the 1980s. Since then, environmental policies regulating SOx emissions successfully reduced the atmospheric load. On average, the forcing of the year 2000, representing present day, equals that of the 1950s. Spatially, the forcing maxima experienced a shift from the northwest to the southeast during the century. The ship emissions of sulfur keep increasing since the 1980s, hence their relative contribution to the sulfate load and radiative forcing constantly increased, from 3% in the 1980s to over 10% in the year 2000. Forcing is strongest during summertime, with a seasonal mean of −2.7 W m−2 in the 1980s and −1.2 W m−2 in summer 2000. The mean forcing efficiency is slightly reduced from −246 W (g sulfate)−1 in the 1900s to −230 W (g sulfate)−1 in the year 2000, and it declines with changed geographical distribution of sulfur emissions.