Will Dunham, PlanetArk 13 Mar 09;
WASHINGTON - Visibility on clear days has declined in much of the world since the 1970s thanks to a rise in airborne pollutants, scientists said on Thursday.
They described a "global dimming" in particular over south and east Asia, South America, Australia and Africa, while visibility remained relatively stable over North America and improved over Europe, the researchers said.
Aerosols, tiny particles or liquid droplets belched into the air by the burning of fossil fuels and other sources, are responsible for the dimming, the researchers said.
"Aerosols are going up over a lot of the world, especially Asia," Robert Dickinson of the University of Texas, one of the researchers, said in a telephone interview.
Dickinson and two University of Maryland researchers tracked measurements of visibility -- the distance someone can see on clear days -- taken from 1973 to 2007 at 3,250 meteorological stations worldwide.
Aerosols like soot, dust and sulfur dioxide particles all harmed visibility, they said in the journal Science.
The researchers used recent satellite data to confirm that the visibility measurements from the meteorological stations were a good indicator of aerosol concentrations in the air.
The aerosols from burning coal, industrial processes and the burning of tropical forests can influence the climate and be a detriment to health, the researchers said.
Other pollutants such as carbon dioxide and other so-called greenhouse gases are transparent and do not affect visibility.
The data will help researchers understand long-term changes in air pollution and how these are associated with climate change, said Kaicun Wang of the University of Maryland.
"This study provides basic information for future climate studies," Wang said in a telephone interview.
The scientists blamed increased industrial activity in places like China and India for some of the decreased visibility, while they said air quality regulations in Europe helped improve visibility there since the mid-1980s.
The aerosols can have variable cooling and heating effects on surface temperatures, reflecting light back into space and reducing solar radiation at the Earth's surface or absorbing solar radiation and heating the atmosphere, they added.
(Editing by Maggie Fox)
Pollution dims skies as well as befouling the air
Yahoo News 12 Mar 09;
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.
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On the Net:
Science: http://www.sciencemag.org
NOAA: http://www.noaa.gov
Environmental Science and Technology: http://pubs.acs.org/journal/esthag?cookieSet1
