"This study provides even stronger scientific evidence that global warming will result in catastrophic species loss across the planet," said Jay Malcolm, an assistant forestry professor at the University of Toronto and a lead author of the study with scientists in the United States and Australia.

Last month, a U.N. study said humans were responsible for the worst spate of extinctions since the dinosaurs and urged unprecedented extra efforts to reach a U.N. target of slowing the rate of losses by 2010.

Scientists disagree about how far global warming is to blame compared with other human threats such as deforestation, pollution and the introduction of alien species to new habitats.

The new study looked at 25 "hotspots"--areas that contain a big concentration of plants and animals--and projected that 11.6 percent of all species, with a range from 1 percent to 43 percent, could be driven to extinction if levels of heat trapping-gases in the atmosphere were to keep rising in the next 100 years.

The range would mean the loss of thousands, or tens of thousands, of species. The report gave a wide range because of uncertainties, for instance, about the ability of animals or plants to move toward the poles if the climate warmed.

"Areas particularly vulnerable to climate change include the tropical Andes, the Cape Floristic region (on the tip of South Africa), southwest Australia, and the Atlantic forests of Brazil, Paraguay and Argentina," it said.

Species in many of these regions have limited escape routes. Rare plants, antelopes, tortoises or birds found only on the southern tip of Africa, for instance, cannot move south because the nearest land is thousands of miles away in Antarctica.

The scientists said their study broadly backed the findings of a 2004 report in the journal Nature that suggested global warming could commit a quarter of the world's species to extinction by 2050. No one knows how many species are on earth, with estimates ranging from 5 million to 100 million.

"It isn't just polar bears and penguins that we must worry about any more," said Lee Hannah, co-author of the study and senior fellow for climate change at Conservation International in the United States.

"We used a completely different set of methods (from the Nature study) and came up with similar results. All the evidence shows that there is a very serious problem," he said.

Global warming is widely blamed on rising concentrations of carbon dioxide in the atmosphere linked to emissions of gases from burning fossil fuels in cars, factories and power plants.

The U.N.'s Kyoto Protocol obliges about 40 nations to cut emissions by at least 5.2 percent below 1990 levels by 2008 to 2012.

President Bush pulled the United States out in 2001, arguing that Kyoto was too costly and wrongly excluded poor nations. Bush instead favors big investments in new technology to break what he has called a U.S. addiction to oil..