"If nothing is done, the earth will have warmed by 2.0 Celsius (3.6 Fahrenheit) above pre-industrial levels by some time between 2026 and 2060," the WWF said in a report.

Few scientists have estimated such an early date for a 2.0C rise, seen by the WWF as a threshold that may spur "dangerous" warming, raising sea levels and causing more floods, storms or droughts and driving some species to extinction.

World temperatures have already risen by about 0.7C since 1750 with most scientists blaming a build-up of heat-trapping gases like carbon dioxide emitted by burning fossil fuels in factories, power plants and cars.

The European Union and many other environmental groups say that governments should cap emissions of greenhouse gases to try to prevent a 2.0C temperature rise. The United States has rejected binding caps under the UN's Kyoto protocol.

At some point, some scientists fear that rising temperatures could cause a runaway warming, for instance by melting permafrost in Siberia that could in turn release deposits of heat-trapping methane to the atmosphere.

"Time is running out to avoid a two degree rise," said Mark New, a climate expert at England's Oxford University who made the 2026-60 projections in the report commissioned by the WWF.

TIME BOMB?

He told Reuters his study was based on a review of climate models used by the UN climate panel in its latest 2001 report. Another international report last week said that rising temperatures were a ticking time bomb for the climate.

Others scientists say that such projections are scaremongering and reckon temperatures will rise far less sharply, if at all, because of the buildup of greenhouse gases.

New's study projected that the Arctic would warm by 3.2-6.6C if the globe warmed by 2.0C overall.

In the Arctic, such a warming could melt polar ice in summer by 2100, pushing polar bears towards extinction. On land, forests would grow further north, overrunning tundra that is a habitat for birds including snow buntings and terns.

"Global warming threatens to wreak havoc on the traditional ways of life of Inuit, putting an end to our hunting and food sharing culture," said Sheila Watt-Cloutier, chair of the Inuit Circumpolar Conference.

The Arctic warms faster than the global average because dark water and land, once uncovered, soaks up more heat than snow or ice. A report by 250 scientists last year also projected a fast warming in the Arctic that would also open new shipping routes and make the region accessible for oil and gas exploration.

The WWF report is to be presented at a conference in Exeter, England, on Feb. 1-3. The talks will focus on a 1992 UN convention whose goal is to stabilise greenhouse gases at levels meant to prevent "dangerous" human interference on the climate.

The convention does not define what it means by "dangerous" climate change.