Atmospheric Science

Constraints from Above

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Science  07 Sep 2012:
Vol. 337, Issue 6099, pp. 1150
DOI: 10.1126/science.337.6099.1150-d
CREDIT: ISTOCKPHOTO

Atmospheric aerosols exert their largest influence on climate through the indirect effects that they have on clouds. These indirect effects, which influence cloud formation, lifetimes, and radiative properties, contribute the largest uncertainty in estimates of the radiative forcing of past and future climate change. Measuring the magnitude of the aerosol indirect effect is difficult, though, in large part due to the competing effects of meteorological variables such as temperature, pressure, relative humidity, and convection. Wang et al. use results from a collection of global climate models to suggest a way in which one component of the aerosol indirect effect, liquid water path, might be better determined by satellite observations of clouds. Their analysis indicates that the liquid water path response to aerosol perturbation is significantly smaller than calculated by most models and that aerosols seem to have a substantially smaller impact on shortwave cloud radiative forcing over the oceans than current global climate models suggest. Though much more work is needed to quantify satellite-derived estimates of cloud properties and the aerosol indirect effect, this research reveals another piece of a complex mosaic of cause and effect.

Geophys. Res. Lett. 39, L15709 (2012).

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