CLIMATE SCIENCE: Black Carbon

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Science  05 Aug 2005:
Vol. 309, Issue 5736, pp. 852c
DOI: 10.1126/science.309.5736.852c

Global climate models are often used for detection and attribution experiments that assign cause to observed variations in climate. These studies have shown that most of the global warming that has occurred over the past 100 years has been caused by increasing concentrations of atmospheric greenhouse gases, and that warming has been moderated by the cooling effect of sulfate aerosols (which reflect sunlight back into space). However, black carbon aerosols have not been included explicitly in these simulations, despite suspicions that they could have a significant effect on the global radiative energy balance, perhaps even outweighing that of sulfate aerosols, because black carbon, unlike sulfate, absorbs solar radiation and causes atmospheric heating.

Jones et al. report results from a detection and attribution analysis that includes black carbon aerosols, as well as sulfate aerosols and greenhouse gases. They find that black carbon is not as important as sulfate and that its inclusion does not change the conclusion that 20th-century warming is due mostly to the positive forcing of greenhouse gas variations. Nevertheless, the magnitude of the effect of black carbon aerosols cannot be evaluated precisely, and black carbon can influence the radiative properties of Earth in other ways, such as by decreasing the albedo of snow. — HJS

Geophys. Res. Lett. 32, 10.1029/2005GL023370 (2005).

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