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Earth's tropical zone 'on the move'

July 06, 2009 12:10 IST

A new scientific review has revealed that the Earth's tropical zone is expanding, possibly moving cyclones, rainfall patterns, pests, and diseases.

An international team, led by James Cook University researchers, has based on its findings after looking at 70 research papers and reports from scientists and institutions right around the world.

Researchers found that of particular concern were regions, which border the subtropics and currently experience a temperate Mediterranean climate.

"Such areas include heavily populated regions of southern Australia, southern Africa, southern Europe, Mediterranean-Middle East region, south-western United States, northern Mexico, and southern South America -- all of which are predicted to experience severe drying.

"If the dry subtropics expand into these regions, the consequences could be devastating for water resources, natural ecosystems and agriculture, with potentially cascading social, environmental and health implications," team leader Prof Steve Turton said.

According to the researchers, the review suggests while these areas could experience an increased frequency of droughts, the expansion of the tropical zone could result in extreme rainfall events and floods to regions, and a poleward shift in the paths of extra-tropical and possibly tropical cyclones in the next 100 years.

"A further implication of the expansion of tropical zone is the possible expansion of tropical associated diseases and pests," Prof Turton said.

The tropical zone is commonly defined geometrically as the portion of the Earth's surface that lies between the Tropics of Cancer and Capricorn at 23.5 degrees latitude north and south respectively.

"However, while evidence is accumulating for the widening of the tropical belt and shifts in other climatic events, there is still much uncertainty regarding the degree of the expansion and the mechanisms which are driving it.

"For example, across the studies reviewed the estimates of the increase in the tropics vary from 2.0 to more than 5 degrees of latitude approximately every 25 years. That makes the minimum agreed expansion of the Topics zone equivalent to around 300 kilometres.

"This variation of estimates makes predicting future shifts difficult. Estimates for the expansion of the tropical zone in next 25 years range from approximately 222 kilometres to more than 533 kilometres depending on which estimate is used," the review concluded.

The tropics currently occupy approximately 40 per cent of the Earth's land surface and are home to almost half of the world's human population and account for more than 80 per cent of the Earth's biodiversity.

The majority of the world's endemic animals and plants, which are found nowhere else on earth, are found in the tropics and are adapted to the climatic conditions.

"Thus, the implications of a poleward expansion of the tropical and subtropical zones are immense and the effects could result in a variety of social, political, economic and environmental implications," the review said.

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