Soot Is Cited as Big Factor in Global Warming
December 25, 2003
By THE ASSOCIATED PRESS
WASHINGTON, Dec. 24 - NASA scientists say soot, mostly from
diesel engines, is causing as much as a quarter of all
observed global warming by reducing the ability of snow and
ice to reflect sunlight.
Their findings on how soot affects reflective ability raise
new questions about climate change caused by humans.
"We suggest that soot contributes to near worldwide melting
of ice that is usually attributed solely to global
warming," the scientists, Dr. James E. Hansen and Dr.
Larissa Nazarenko, wrote in a paper published this week in
The Proceedings of the National Academy of Sciences.
"Soot is a more all-around `bad actor' than has been
appreciated," the scientists wrote.
Soot is blackened material formed mainly from carbon
particles that are, along with salts and dust, byproducts
of burning fossil fuels and vegetation.
Dr. Hansen, director of NASA's Goddard Institute for Space
Studies, and Dr. Nazarenko, a staff associate at Goddard,
found that soot was twice as potent as carbon dioxide in
changing global surface air temperatures in the Arctic and
the Northern Hemisphere.
Greenland may be an exception, they said, because it is
downwind from Canadian forests and has little man-made
The biggest source of soot in developed countries is diesel
fuel, they said, but major sources elsewhere include
burning wood, animal dung, vegetable oil and other
Dr. Hansen told The Associated Press that he and his
co-author estimated that the soot effect was equivalent to
putting a 1-watt bulb, the size of a miniature bulb on a
Christmas tree, over every two square yards in the Northern
Hemisphere. The effect is greater in northernmost snow
regions, and almost nonexistent in the tropics, he said.
Levels of airborne soot as high as about 100 parts per
billion were found in the Alps, enough to reduce the snow's
ability to reflect light rather than absorb it from about
98 percent down to 80 percent to 90 percent, Dr. Hansen
said. In spring and summer, as the snow melts and some soot
accumulates on the surface, the remaining snow is even
darker, he said.