Aerosol Effect -- Cool But Short: Just as painting a house white increases reflectivity of sunlight and reduces heat absorption, aerosols scatter solar radiation and increase the reflectivity of clouds. In a recent lecture to the American Association for Aerosol Research, atmospheric scientist Stephen Schwartz concluded that this "whitehouse effect" has decreased planetary absorption of solar radiation, resulting in a cooling influence on the climate over the industrial period. This cooling influence of aerosols may be of a global-average magnitude comparable to the warming influence of infrared absorbing gases, but present estimates are highly uncertain. The key implication is that the cooling influence has been offsetting the warming influence, meaning that the greenhouse effect is actually greater than indicated in the temperature record over the industrial period -- the true extent is hidden by the counter-vailing whitehouse effect. However, the uncertainty associated with the whitehouse effect is so great that no quantitative conclusions can yet be drawn. Reasons for this uncertainty include the nonuniform geographical distribution and highly variable loading and properties of these aerosols compared to greenhouse gases.

Aerosol particles reside in the atmosphere for a few days to a week compared to greenhouse gases, which reside in the atmosphere for decades to centuries. This means that to whatever extent the whitehouse effect is offsetting the greenhouse effect, only a week's worth of aerosol emissions offsets at least a decades' worth of greenhouse gas emissions. This disparity indicates that any scheme to deliberately offset the warming "greenhouse" effect by using the cooling "whitehouse" effect would be unworkable. Further research, supported by DOE's Office of Energy Research, Atmospheric Radiation Measurement (ARM) program, is directed at reducing uncertainties in the quantitative relation between aerosol loading and radiative forcing. (Contact Stephen E. Schwartz, BNL, (516) 344-3100, fax (516) 344-2887, e-mail ses@bnl.gov)

Related links: American Association for Aerosol Research

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