Climate Science

Clearing up Cloudy Data

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Science  13 Jun 2008:
Vol. 320, Issue 5882, pp. 1396
DOI: 10.1126/science.320.5882.1396a

Aerosols have a huge influence on climate, largely through how they affect clouds by what is termed their indirect effect. The indirect aerosol effect is the sum of two distinct phenomena: first, the response of cloud drop density and size to changes in aerosol properties; and second, the response of cloud albedo to changes in cloud drop density and size. Both components must be known to determine the whole effect, but most of the experimental and field studies conducted to date have addressed only the first process, leaving large uncertainties. Roberts et al. describe a method to quantify both phenomena at once, thereby enabling direct observation of aerosol-cloud-albedo interactions. They use a stack of three autonomous unmanned aerial vehicles below, at, and above cloud level, to simultaneously measure the radiometric and microphysical properties of individual clouds. Their results therefore pave the way for resolving the largest current source of uncertainty in the quantification of the radiative forcing of climate. — HJS

Proc. Natl. Acad. Sci. U.S.A. 105, 7370 (2008).

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