HR: 17:35h
AN: A54B-06    [Abstracts]
TI: Impact of Surface Solar Dimming and Brightening on the Climate System
AU: * Wild, M
EM: martin.wild@env.ethz.ch
AF: Institute for Atmospheric and Climate Science ETH Zurich, Universitaetsstr. 16, Zurich, 8092, Switzerland
AB: The author's institute maintains two databases for the worldwide measured solar radiation incident at the Eart's surface, the Global Energy Balance Archive (GEBA), and the Baseline Surface Radiation Network (BSRN). An analysis of these comprehensive datasets suggests that solar radiation incident at the surface has not been stable over time but underwent significant decadal variations. This is seen in a decline in surface solar radiation from the 1960s to the 1980s („global dimming"), with a recovery thereafter at widespread locations („global brightening"). As potential explanation for these variations, both changes in clouds and aerosol have been put forward. An analysis of synop and satellite-based cloud data over Europe suggests, that changes in cloud amount cannot explain the distinct reversal from solar dimming to brightening seen over Europe. This points to aerosol direct/indirect effects as a key explanation for the dimming to brightening transition. The reversal from dimming to brightening may be related to reduced aerosol concentration due to more effective air pollution measures and the breakdown of the economy in the former communist countries, leading to cleaner and more transparent atmospheres. Changes in surface solar radiation may also leave their imprint in the diurnal temperature range. Trends in diurnal temperature ranges show, after decades of decline, a distinct tendency to level off since the mid 1980s. They suggest that surface solar dimming was effective in masking greenhouse warming, but only up to the 1980s, when dimming gradually transformed into brightening. With this transition, the uncovered greenhouse effect started to reveal its full dimension, as manifested in a rapid temperature rise. The reversal from surface solar dimming to brightening may also affect biomass productivity in energy-limited environments, and should leave a significant imprint on vegetation. Wild, M et al. 2005: From dimming to brightening: Decadal changes in solar radiation at the Earth's surface. Science, 308, 847-850. Wild, M., Ohmura A., Makowski, K., 2007: Impact of global dimming and brightening on global warming. GRL 34, L04702. Norris, J.R., and Wild, M., 2007: Trends in direct and indirect aerosol radiative effects over Europe inferred from observed solar "dimming" and "brightening", JGR (in press).
DE: 3311 Clouds and aerosols
DE: 3359 Radiative processes
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly