Fires main threat to Amazon in drier climate: study

By Alister Doyle, Environment Correspondent

OSLO (Reuters) - Fires set by people will be the biggest threat to the Amazon rainforest in coming decades linked to a drier climate caused by global warming, researchers said on Monday.

They said swathes of the forest were more likely to be killed by blazes raging out of control than by a more gradual shift towards savannah caused by more frequent droughts predicted by the U.N. Climate Panel in a 2007 report.

"Fire associated with human activity and drying is likely to be what eliminates the forest rather than the gradual stress of climate change," Mark Bush of the Florida Institute of Technology and U.S.-based colleagues wrote in a study.

Examining the history of fire in Amazonia, they said people were the overwhelming cause of burning in the past 3,000 years with lightning strikes rarely igniting the wet forest. "The Amazon doesn't burn unless people burn it," Bush told Reuters.

A drier climate, more human settlements and burning to clear land for farming would bring risks of ever wider fire damage, they wrote in the British journal Philosophical Transactions of the Royal Society B devoted to the Amazon.

Indigenous people in the Amazon basin before Christopher Columbus sailed the Atlantic in 1492 "burned the forest to clear it for agriculture, and perhaps also to improve hunting," they wrote of charcoal records. "After the time of European contact, fires became much scarcer."

The U.N. Climate Panel predicted in a 2007 report that rising temperatures and drier soil would "lead to gradual replacement of tropical forest by savannah in eastern Amazonia" by 2050.

It also said there was a risk of a "significant" loss of the diversity of species of animals and plants because climate change could drive many to extinction. Its models did not assess fire risks.