Wednesday, September 13, 2006

What May Happen if Global Average Temperatures Rise by 3C or More

Forest fires, droughts and floods are all likely to become more severe and more common if global warming heats the planet as seriously as some scientists predict.

A study of what may happen if global average temperatures rise by 3C or more over the next 200 years suggests that extreme weather events are going to be more frequent and more severe.

The study also warns that vegetation could lose its ability to be a net absorber of carbon dioxide, and instead become a net producer of greenhouse gases.

Marko Scholze, a climate scientist at Bristol University, said theresearch showed that if the global average temperature rose by more than 3C over the next 200 years, as widely predicted, there is a higher risk of extreme instances of forest fires or floods.

"We looked at these extreme events and what we found was that a once-in-a-hundred-year event can become a once-in-a-ten-year event by the end of the century," he said.

The study analysed 52 computer models of the global climate. Researchers found that as global temperatures rose, so did the risk of forest fires, droughts and flooding caused by the sudden runoff of heavy rainfall.

Even if we stopped emitting greenhouse gases today, global temperatures are still likely to continue increasing because of the inherent inertia of the global climate system.

With a 2C increase in average temperatures, there is a 30 per cent increased risk of significant deforestation in the northern forests of Eurasia, eastern China, Canada, and the tropical rainforests of central America and the Amazon. This risk would rise to 60 per cent and affect wider areas if temperatures rose by 3C.

Other effects of higher temperatures include less freshwater and a greater risk of more intense droughts in west Africa, central America, southern Europe and the eastern states of America. But one of the most dangerous scenarios depicted in the study involves land vegetation. "Terrestrial vegetation takes up carbon dioxide. About half of what we emit is taken up by plants," Dr Scholze said.

But when temperatures rise above 3C, the absorbing effect of carbon dioxide by land plants is outweighed by the increase in organic decomposition within the soil, which increases with temperature. "We then see that we don't only have the carbon emissions from humans, but from the terrestrial biosphere as well," Dr Scholze said.

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