Smoke and Climate Change

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Science  10 Jul 2009:
Vol. 325, Issue 5937, pp. 153-154
DOI: 10.1126/science.1176991

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Anthropogenic pollution forms small liquid or solid particles in the atmosphere. These aerosols—emitted directly, for example, as soot particles from smoke (see the figure), or formed from pollution gases, such as sulfate particles—are of nanometer to micrometer size. Some particles absorb sunlight, contributing to climate warming; others reflect sunlight, leading to a relative cooling. The global mean effect of anthropogenic aerosols is a cooling, but the relative contributions of the different types of aerosols determine the magnitude of this cooling. On page 187 of this issue, Myhre (1) offers new insights into these aerosol effects on climate by showing that the relative increase in light absorption by anthropogenic smoke since preindustrial times was larger than the increase in light scattering by other anthropogenic aerosols. His results substantially advance the level of scientific understanding of how aerosols affect climate.