15
January 2004
Pollutants that cool
Anthropogenic aerosols (tiny particles that contribute to smog and haze) can enhance cloud reflectivity by increasing the number concentration of cloud droplets. Many small droplets scatter more sunlight back into space than fewer large ones, so in theory an accumulation of aerosol particles can produce cooling, known as the indirect aerosol effect. The Intergovernmental Panel on Climate Change has concluded that the indirect effect of aerosols might be negligible, in part because of a lack of direct evidence that this mechanism affects the balance between incoming solar radiation and outgoing infrared. New data from sites of polluted (Oklahoma) and clean (Alaska) air show that aerosol pollutants affect cloud optical depth significantly, at a magnitude expected from the indirect aerosol effect, and hence that this effect is an important factor in climate.
Observational evidence of a change in radiative
forcing due to the indirect aerosol effect
JOYCE E. PENNER, XIQUAN DONG & YANG CHEN
Nature 427, 231–234 (2004); doi:10.1038/nature02234
| First
Paragraph | Full
Text (HTML / PDF) |
