Global dimming and brightening: An update beyond 2000

Abstract

This study investigates recent variations in downwelling surface solar radiation inferred from a comprehensive set of ground-based observational records updated for the period 2000-2005. Surface radiation data beyond the year 2000 are particularly interesting as they provide independent and complementary information to the ambitious satellite programs which became operational with the beginning of the new millennium. The surface records suggest a continuation of the surface solar brightening beyond 2000 at numerous stations in Europe and the United States, as well as parts of east Asia (Korea). Surface solar radiation variations in Europe after 2000 are dominated by a large positive anomaly in the year 2003 with its unprecedented summer heat wave, exceeding 10 Wm -2 on an annual and 20 Wm -2 on a summer mean basis in central Europe. The brightening seen at sites in Antarctica during the 1990s, influenced by a recovery from the low atmospheric transparency after the Mount Pinatubo volcanic eruption in 1991, fades after 2000. The brightening tendency also seems to level off at sites in Japan. In China there is some indication for a renewed dimming, after the stabilization in the 1990s. A continuation of the long-lasting dimming is also noted at the sites in India. Overall, the available data suggest continuation of the brightening beyond the year 2000 at numerous locations, yet less pronounced and coherent than during the 1990s, with more regions with no clear changes or declines. Therefore, globally, greenhouse warming after 2000 may be less modulated by surface solar variations than in prior decades. Copyright 2009 by the American Geophysical Union.