Global dimming and global brightening - an analysis of surface radiation and cloud cover data in northern Europe

In the present study, surface solar radiation data from 11 stations in northwestern Europe and the European Arctic are presented in the context of the ongoing discussion on global dimming and global brightening. The surface solar radiation records are compared to records of cloud cover, and to qualitative information on aerosol concentrations and atmospheric circulation patterns, in order to explain the temporal variations. Through simple statistical analyses, we examine annual trends as well as trends for individual months, and compare the results between the stations. Comparisons are also made between different time periods within the records. We find that Surface solar radiation changes in the region considered, even at the remote arctic stations, correspond well with trends found in global studies, with a significant decrease from the 1950s to the 1980s, followed by a slight increase in recent years. At stations that stand out from the general pattern, the deviations can be explained by variations in cloud cover in most cases. There has been a general tendency to attribute the majority of the observed surface solar radiation trends to aerosol changes caused by changes in anthropogenic emissions. This study stresses the importance of the contribution of clouds and the atmospheric circulation to global dimming and global brightening. Copyright (C) 2008 Royal Meteorological Society