Pollution leads to global dimming
2009-03-13 10:08
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.
Soot, dust and sulfur dioxide
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.