The indirect aerosol effect over Europe

Abstract

In order to assess the influence of anthropogenic emissions on cloud albedo over Europe a reprocessed set of satellite measurements from 1985 to 1999 was investigated. Special emphasis was given to the Central European main emission area, including the so-called 'Black Triangle' which covered parts of Germany, the Czech Republic and Poland. Due to the decrease of aerosol precursor gases the analysis reveals a pronounced decrease of cloud albedo of about 2% from the late 80s to the late 90s. During winter in source regions of anthropogenic particulate matter emissions the cloud reflectance is more than 5% lower referring in addition to an absorption effect caused by black carbon in clouds. The comparison with emission data as well as model results of long range transport over Europe strongly supports the conclusion that the changed indirect aerosol effect is responsible for significantly changed cloud optical properties. Radiative transfer calculations indicate for the classical Twomey effect a change in radiative forcing of about 1.5 W/m2 from the late 80s to the late 90s. In addition during winter a radiative forcing of about 3 W/m2 due to the absorption effect for both the late 80s and the late 90s is estimated.