Until now, scientists have tended to expect that man-made particulate air pollutants reflect heat, causing cooling in polluted areas, contrary to the general trend of global warming. According to experts’ predictions, then, whilst temperatures are rising globally, they should be decreasing in the south-eastern United States and in China. However, whilst the US climate has followed this theory, China has actually warmed slightly over the last 50 years, say researchers from North Carolina State University (NCSU) and the National Climate Centre of China.

This may be due to the presence of differing types of aerosols in the two areas, say researchers, following a study of the effects of the 1991 eruption of the Filipino volcano, Mount Pinatubo. During the last half century, the amount of carbon soot pollution over China has increased, coinciding with a rise in temperature. However, when the volcano erupted it emitted 30 megatons of sulphur dioxide into the atmosphere, producing sulphate aerosols, which resulted in cooler temperatures around the world, including in the south-eastern US and in China.

By 1993, once the sulphate aerosols had dissipated, temperatures increased again in China, but not in the south-east US.

“The [US] Southeast receives sulphate aerosols blown over the Appalachians from industrial manufacturing in the Ohio River Valley,” said Dr Vinod Saxena, Professor of Meteorology at NCSU, and one of the researchers on the project. “Sulphate aerosols are believed to decrease temperatures by having the same effect as painting a house roof white: they reflect solar radiation back into space.” The project’s findings correspond to those of research into pollution over the Indian ocean, Saxena explained to edie (see related story)

Saxena believes that his research indicates that the Kyoto treaty, as it stands, would not sufficiently combat global warming and needs to restrict emissions of carbon aerosols by developing nations such as China and India. Research indicates that such aerosols are the second most important cause of global warming, following carbon dioxide, says Saxena (see related story).

“The air masses don’t know any international boundaries,” said Saxena. “Five days after soot is emitted into the atmosphere in China, it shows up on the West Coast of the United States.” More research is needed on the sources of carbon soot aerosols and how they are distributed in the atmosphere, he added.

A report on the research is published in the journal, Geophyisical Research Letters.

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