Global and Regional Climate Changes due to Soot Aerosols

Soot from burning of fossil fuels, biomass and biofuels, is emerging as a major factor in global and regional climate changes. Globally, its positive forcing may be second only to carbon dioxide. Regionally, however, particularly over Asia, Africa and the Arctic, its effects may be just as important as that due to CO2. It is estimated to contribute to multi- decadal or longer long-term trends in surface and atmospheric temperatures, monsoon circulation and rainfall patterns, and early melting of snow packs and sea ice. Our understanding of the magnitude of the soot emission, its atmospheric concentrations, the radiative forcing both directly and through its interactions with clouds, sea ice and snow surfaces are all at a very preliminary stage. One of the most challenging aspects of the soot-climate issue is that, because of the large spatial and temporal variations of soot concentrations in the atmosphere, it can alter the sea surface temperature gradient (between northern and southern hemisphere) which is one of the important regulators of the inter-tropical-convergence-zone and the monsoon circulation and thus the land rainfall. I will summarize our current understanding of the soot-climate interactions and highlight major outstanding issues relating to global and regional climate, including the sensitivity of the Asian monsoon system, the tropical and extra tropical glaciers, and the regional precipitation patterns to large soot loading in the tropical regions. Finally, I will discuss reduction of soot emissions as a potential option for mitigating large climate changes.