Climate response to anthropogenic aerosol forcing using the NCAR CCM3 coupled to a slab ocean
Abstract
In order to estimate the climatic impact of anthropogenic aerosols, a set of 50-year simulations have been carried out using an extended version of the NCAR CCM3 global climate model, coupled to a slab ocean. The extensions consist of prognostic cloud water (Rasch-Kristjansson scheme) and a new treatment of aerosols. The direct and indirect effect of sulfate and black carbon are calculated, based on a life-cycle scheme that, combined with natural continental and maritime aerosols, enables estimates of size-distributed particle properties. The size distributions account for condensation, coagulation, cloud processing and humidity swelling, and are used both for computing optical properties and CCN activation. The largest negative contribution to aerosol radiative forcing is found over SE Asia, followed by the North Atlantic Ocean and Europe. The main focus of the talk will be simulations where the climate system is allowed to respond to the aerosol forcing. The largest temperature reduction is found in the Arctic, in particular during fall and winter when the regional contribution to the forcing is small. This is shown to be a consequence of a strong ice albedo feedback at high latitudes, as well as the formation of a shallow anticyclone over the Arctic in the dark season. In a sensitivity experiment where the ice albedo feedback was suppressed, the cooling in the Arctic was reduced, while the mid-latitude cooling was enhanced at the same time. Another signal that is statistically significant is a southward displacement of the ITCZ, due to the inter-hemispheric differences in aerosol forcing. This leads to, e.g., reduced precipitation over the Sahelian region in Africa.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....9091K