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2009-03-13 04:50:04
WASHINGTON The skies are dimming, for most of the world. Increases in
airborne pollution have dimmed the skies by blocking sunlight over the past 30
years, researchers report in Friday's edition of the journal Science.
While decreases in atmospheric visibility known as global dimming have been
reported in the past, the new study compiles satellite and land-based data for
a longer period than had been available.
"Creation of this database is a big step forward for researching long-term
changes in air pollution and correlating these with climate change," Kaicun
Wang, assistant research scientist in the University of Maryland, said in a
statement. "And it is the first time we have gotten global long-term aerosol
information over land to go with information already available on aerosol
measurements over the world's oceans."
They reported that dimming is occurring everywhere except Europe, where
declines in pollution have resulted in brighter skies.
Changes in aerosols can affect weather and also may have an impact on climate,
though past studies have been inconclusive. These pollutants can result in
cooling by reflecting sunlight back into space, but they also can absorb solar
energy, warming the atmosphere.
Researchers at the National Oceanic and Atmospheric Administration, meanwhile,
warned that suggestions for a high-atmosphere "sunshade" of particles to battle
global warming could reduce energy production from solar power plants.
Those proposals are aimed at blocking sunlight that can be absorbed by
so-called greenhouse gases like carbon dioxide, warming climate.
But airborne particles also scatter light that does get through, and that
diffuse light cannot be used by solar energy concentrating systems that produce
electricity, Daniel Murphy, a scientist at NOAA's Earth System Research
Laboratory in Boulder, Colo., reported in the journal Environmental Science and
Technology.
Flat photovoltaic and hot water panels, commonly seen on household roofs, use
both diffuse and direct sunlight, so they would be less affected.