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article imageIncreasing air pollution makes climate debate difficult

By Bart B. Van Bockstaele     Mar 13, 2009 in Environment
Air pollution darkens the sky and this may have an effect on climate change. There is a lot of uncertainty regarding this effect, however. It is not even certain whether the earth's skies are actually darkening or brightening.
Nature reports that an extensive survey shows that air pollution, harmful to human health, has increased over all populated continents, except Europe since 1973.
In 2005, two studies published in Science had concluded that a trend of global dimming that began in the 1950s had changed since 1990 by global brightening. Faster global warming would be the probably result because more solar radiation would reach the surface of the planet.
A new study published in Science now concludes that the skies have actually become dimmer between 1973 and 2007. In Europe, however, the skies have become cleaner than 30 years ago. This is caused by the collapse of communism, which has led to a fall in industrial production. New air quality regulations have also had a big effect since then. In North America, air quality has not changed much during the period.
The scientists of the University of Maryland have used visibility data from 3,250 meteorological stations all over the world. Visibility data are a good indicator for aerosol (suspension of very fine dust or liquid in air) production. They have found that the strongest dimming occurred in South Asia and South America.
The problem now is that it is not known what the net effect of aerosol pollution is. Some aerosols prevent clouds from forming, others encourage cloud formation. Some aerosols absorb solar radiation, rather than reflecting it back into space.
Previous studies measured incoming solar radiation, not visibility, and that may have something to do with the idea that the skies are brightening.
A lot of unanswered questions remain. That much is certain. However, the scientists are optimistic that the air in China could become cleaner quite soon, just as it did in Europe in the 1980s and before that in North America, if China would replace coal by oil and natural gas, and if there would be more widespread use of particulate filters in cars and factories.
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