Friday, 5 June 2009

THE acres upon acres of lush tropical forest in the Amazon and tropical Africa are often referred to as the planet's lungs. But what if they are also its heart? This is exactly what a couple of meteorologists claim in a controversial new theory that questions our fundamental understanding of what drives the weather. They believe vast forests generate winds that help pump water around the planet.

If correct, the theory would explain how the deep interiors of forested continents get as much rain as the coast, and how most of Australia turned from forest to desert. It suggests that much of North America could become desert - even without global warming. The idea makes it even more vital that we recognise the crucial role forests play in the well-being of the planet.

Scientists have known for some time that forests recycle rain. Up to half the precipitation falling on a typical tropical rainforest evaporates or transpires from trees. This keeps the air above moist. Ocean winds can spread the moisture to create more rain. But now Victor Gorshkov and Anastassia Makarieva of the St Petersburg Nuclear Physics Institute in Russia say that forests also create winds that pump moisture across continents.

"In conventional meteorology the only driver of atmospheric motion is the differential heating of the atmosphere. That is, warm air rises," Makarieva and Gorshkov told New Scientist. But, they say, "Nobody has looked at the pressure drop caused by water vapour turning to water." The scientists, whose theory is based on the basic physics that governs air movement have dubbed this the "biotic pump" and claim it could be "the major driver of atmospheric circulation on Earth". This is a dramatic claim. The two Russians argue that their biotic pump underlies many pressure-driven features of the tropical climate system, such as trade winds, and helps create intense local features like hurricanes.

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