Reducing the rate at which Amazonian rain forests are disappearing by only 10 percent, for example, would yield 1.5 to 9.1 billion euros (2.2 to 13.5 billion dollars), depending on world carbon emission prices, researchers calculated.

That money could then be plowed into national conservation efforts that would further mitigate climate change, creating a virtuous circle.

Slow down deforestation by another 20 percent, and the potential income for the region would top 45 billion dollars if carbon prices reached 30 euros per tonne, said the study, one of two dozen scientific papers on the future of the Amazon released Monday by The Royal Society in Britain.

Reigning in the destruction of the world's tropical forests has become a key focus of climate change efforts.

"The ongoing degradation of Amazonia is a threat to local climate stability and a contributor to the global atmospheric climate change crisis," noted Richard Betts of the Met Hadley Center for climate prediction in Britain.

Deforestation -- caused by logging, agriculture and development -- in the tropics accounts for up to 20 percent of global emissions of carbon dioxide, making it the second largest driver of global warming after the burning of fossil fuels.

Amazonia accounts for nearly half of those emissions.

Experts are especially alarmed because the impact cuts both ways: climate change threatens to boost the rate at which the Amazon's delicately balanced rain forest dries up, and could push it to a tipping point beyond which recovery would become difficult or impossible.

The UN's Intergovernmental Panel for Climate Change (IPCC) has warned that rising global temperatures could transform much of South America's rain forests into semi-arid savannah-like areas within five decades.

A major UN climate change conference in December for the first time took steps toward extending the international market in carbon credits to "reducing emissions from deforestation and degradation" (REDD).

Under the Kyoto Protocol, countries and companies can buy and sell credits to emit greenhouse gases so as to meet their own treaty obligations.

How to apply this mechanism to deforestation has yet to be worked out. But the basic concept is simple: rich nations unable or unwilling to reduce their own C02 emissions would pay developing countries that agreed to slow the destruction of one Nature's most effective bulwarks against climate change.

Up to now, carbon credits were given only to reforestation projects.

By 2001, some 837,000 square kilometres (323,000 square miles) of Amazonian rain forest has been cleared, some 13 percent of its original area.

Eighty percent of that has been in Brazil, where annual deforestation rates peaked at 27,400 square kilometres (10,600 square miles) in 2004.

In looking at how REDD might be implemented in the Amazon region, Joahnnes Ebeling of EcoSecurities in Britain and Mai Yasue of the University of British Columbia in Vancouver, Canada caution that many barriers remain.

One is a ensuring that only genuine reductions in deforestation are rewarded, and that global markets do not simply shift timber and agricultural operations across borders.

There is also debate on how to set the benchmark against which deforestation efforts are to be measured. Using average annual rain forest loss, for example, would favor those countries with the poorest records to date, and unfairly penalise those that have already tackled the problem with some success.

Corruption is a likewise a problem. Ebeling and Yassue point out that some countries that stand to gain the most from carbon trading schemes may be the least likely to use the money effectively, such as Burma, Bolivia, The Democratic Republic of Congo and Myanmar.

But they also argue that REDD, if successful, could have added benefits beyond putting a break a global warming.

"Tropical deforestation not only contributes to climate change but is also regarded as the single greatest threat to terrestrial biodiversity," they note.

"There is also widespread hopes," they continue, "that REDD will provide resources for human development and poverty relief."

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