GREENBELT, Md., March 4 (UPI) -- NASA researchers said Thursday new data suggest heavy smoke from burning vegetation inhibits cloud formation.
The finding means the cooling effect on global climate of pollutant particles called aerosols may be smaller than previously estimated.
The researchers studied the August-October 2002 burning season in South America's Amazon River basin and found cloud cover decreased from about 40 percent in clean-air conditions to zero in smoky air.
Until recently, scientists thought aerosols such as smoke particles mainly served to cool the planet by shading the surface, either directly, by reflecting sunlight back toward space, or indirectly, by making clouds more reflective. Certain aerosols make clouds' droplets smaller and more numerous, thereby making the clouds more reflective while reducing the amount of sunlight reaching the surface.
The new study, however, suggests smoke aerosols have an indirect effect on climate -- causing a reduction in cloud cover and warming the surface.
