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-------Original Message-------
Date: 05/16/05 07:51:07
Subject: [euratom] Studies show Earth's surface is brighter, reversing a trend
Studies show Earth's surface is brighter, reversing a trend
Change could speed a warming trend, researchers say, but others say
it's not that simple
By KENNETH CHANG
New York Times
GRAPHIC
� LESS REFLECTION, MORE LIGHT: New studies show an increase in
sunlight reaching Earth since 1990.
Reversing a decades-long trend toward "global dimming," the Earth's
surface has become brighter since 1990, scientists have reported.
The brightening means that more sunlight � and thus more heat � is
reaching the ground. That could partly explain the record-high global
temperatures reported in the late 1990s, and it could accelerate the
warming trend.
"We see the dimming is no longer there," said Dr. Martin Wild, a
climatologist at the Swiss Federal Institute of Technology in Zurich.
Wild is the lead author of one of three papers analyzing sunlight
that appear in the May 6 issue of the journal Science.
"If anything, there is a brightening," Wild said.
Some scientists have reported that from 1960 to 1990, the amount of
sunshine reaching the ground dropped at a rate of 2 percent to 3
percent per decade.
The new papers also call attention to a major gap in the
understanding of climate.
Scientists do not exactly know what caused the dimming and
brightening or how these changes affect the rest of the climate
system.
The Earth reflects about 30 percent of the incoming sunlight back
into space.
Slight changes in the reflectivity, possibly caused by changes in
cloud cover and air pollution, can have as much impact on the climate
as greenhouse gases such as carbon dioxide accumulating in the
atmosphere.
"I think what could have happened is the dimming between the '60s
and '80s counteracted the greenhouse effect," Wild said.
"When the dimming faded, the effects of the greenhouse gases became
more evident," Wild added. "There is no masking by the dimming
anymore."
Dr. Rachel Pinker, a professor of meteorology at the University of
Maryland, who led the team that wrote one of the other papers, said
the picture probably isn't that simple.
More sunlight should increase evaporation rates, leading to more
clouds, and the additional cloud cover could then increase the
Earth's reflectivity, limiting the warming effect, she explained.
"It's dangerous to look at dimming at a limited number of locations
and draw conclusions on the global-scale effects," she said.
"I think that's a complex issue," she added.
Finally, a team led by Dr. Bruce Wielicki of NASA's Langley Research
Center in Virginia reports that measurements from the agency's Aqua
satellite show there was a slight decrease in the amount of light
reflected off Earth since 2000, which corresponds to a brightening on
the surface.
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