Washington, March 10: The task of cutting greenhouse gas emissions to avert a dangerous rise in global temperatures may be far more difficult than previous research suggests, say scientists.

In recently published studies, the scientists indicated that the world would have to cease carbon emissions altogether within a matter of decades.

Their findings, published in separate journals over the past few weeks, suggest that both industrialised and developing nations must wean themselves off fossil fuels by as early as middle of this century in order to prevent warming that could change precipitation patterns and dry up sources of water worldwide.

Scientists from the US, Canada and Germany are delivering a simple message: The world must bring carbon emissions down to near zero to keep temperatures from rising further. “The question is, what if we don’t want the Earth to warm anymore?” asked Carnegie Institution senior scientist Ken Caldeira, co-author of a paper published last week in the journal Geophysical Research Letters.

“The answer implies a much more radical change to our energy system than people are thinking about.” Although many nations have been pledging steps to curb emissions for nearly a decade, the world’s output of carbon from human activities totals about 10 billion tons a year and has been steadily rising.

For now, at least, a goal of zero emissions appears well beyond the reach of politicians in the US and abroad.

American leaders are just beginning to grapple with setting any mandatory limit on greenhouse gases. The Senate is poised to vote in June on legislation that would reduce US emissions by 70 per cent by 2050; Democrat Senators Hillary Rodham Clinton and Barack Obama back an 80 per cent cut. Senator John McCain supports a 60 per cent reduction by mid-century.

Democrat Senator Barbara Boxer, who is shepherding climate legislation through the Senate as chairman of the Environment and Public Works Committee, said the new findings “make it clear we must act now to address global warming”. “It won’t be easy, given the makeup of the Senate, but the science is compelling,” she said. “It is hard for me to see how my colleagues can duck this issue and live with themselves.”

James L. Connaughton, who chairs the White House Council on Environmental Quality, offered a more guarded reaction, saying the idea that “ultimately you need to get to net-zero emissions” is “something we’ve heard before”. When it comes to tackling such a daunting environmental and technological problem, he added: “We’ve done this kind of thing before. We will do it again. It will just take a sufficient amount of time.”

Until now, scientists and policymakers have generally described the problem in terms of halting the buildup of carbon in the atmosphere. The UN Framework Convention on Climate Change framed the question two decades ago and many experts talk of limiting CO2 concentrations to 450 parts per million (ppm).

But Caldeira and Oregon State University professor Andreas Schmittner now argue that it makes more sense to focus on a temperature threshold as a better marker of when the planet will experience severe climate disruptions.