The world leaders who met at the United Nations to discuss climate change on Tuesday are faced with an intricate challenge: building momentum for an international climate treaty at a time when global temperatures have been relatively stable for a decade and may even drop in the next few years.
The plateau in temperatures has been seized upon by skeptics as evidence that the threat of global warming is overblown. And some climate experts worry that it could hamper treaty negotiations and slow the progress of legislation to curb carbon dioxide emissions in the United States.
Scientists say the pattern of the last decade — after a precipitous rise in average global temperatures in the 1990s — is a result of cyclical variations in ocean conditions and has no bearing on the long-term warming effects of greenhouse gases building up in the atmosphere.
But trying to communicate such scientific nuances to the public — and to policy makers — can be frustrating, they say.
Mojib Latif, a prize-winning climate and ocean scientist from the Leibniz Institute of Marine Sciences at the University of Kiel, in Germany, wrote a paper last year positing that cyclical shifts in the oceans were aligning in a way that could keep temperatures over the next decade or so relatively stable, even as the heat-trapping gases linked to global warming continued to increase.
But Dr. Latif, who gives about 200 talks to the public, business leaders and officials each year, said he had been met with confusion and even anger when he tried to describe this normal variation in climate while at the same time conveying the long-term threat of global warming.
“People understand what I’m saying, but then basically wind up saying, ‘We don’t believe anything,’ ” he said in a telephone interview.
Other climate researchers dispute Dr. Latif’s forecast, saying that climate cannot be reliably predicted on such a short time scale, though even they agree that sooner or later, cool stretches are inevitable.
Underscoring just how little clarity there is on short-term temperature fluctuations, researchers from Britain’s climate change office, in a paper published in August, projected “an end to this period of relative stability,” with half the years between now and 2015 exceeding the record-setting global temperatures of 1998.
Whatever the next decade may hold, critics of global warming have lost no time in using the current temperature plateau to build their case.
“I think it supports the arguments of those who’ve said, ‘What’s the rush for policy on this issue?’ ” said Patrick J. Michaels, a climatologist affiliated with George Mason University and the Cato Institute, a group opposing most regulatory solutions to environmental problems.
The recent stability of global temperatures makes regular appearances in blog postings disputing the reality of global warming and is frequently invoked by pundits who oppose the climate bill that passed the House this year and is pending in the Senate.
Advocates of such regulatory measures are equally vehement. In a post last week on his blog, Climate Progress, Joseph Romm, a physicist and energy expert affiliated with the liberal Center for American Progress, wrote that statements by climate skeptics about planetary cooling were “nonsense.”
“We need all the unmuffled warnings we can get given that humans are not like slowly boiling frogs, we are like slowly boiling brainless frogs,” he wrote.
The recent spate of years with stable temperatures is particularly noticeable because it followed a seesawing from unusually cool temperatures to unusually hot ones in the 1990s, said Vicky Pope of Britain’s climate agency, called the Met Office.
The 1991 eruption of Mount Pinatubo in the Philippines had a cooling influence, as the volcano threw off veil-like emissions. Then, in 1998, an El Niño episode in the Pacific Ocean set off a record-setting hot spell.
The global average temperature is now only 0.13 degree Fahrenheit higher than it was in 1999, according to the British meteorology office.
A series of unremarkable storm seasons followed the string of destructive storms in 2004 and 2005 that included Hurricane Katrina. And in the Arctic, an extraordinary summer retreat of sea ice in 2007 has been followed by less substantial losses and projections by some researchers of a possible, if temporary, recovery.
Most climate scientists stand firm in their projections of centuries of rising seas and other disruptive effects of a warming planet if humans take no steps to reduce their emissions of greenhouse gases.
In an address to world leaders at the climate summit meeting on Tuesday, Rajendra K. Pachauri, the chairman of the Intergovernmental Panel on Climate Change, which has advised the world’s nations on climate issues for 20 years, described the mounting risk and said, “Science leaves us no space for inaction now.”
A clearer view of whether the recent temperature plateau undermines arguments for dangerous climate change in the long run should come in a few years, as the predictions made by the British climate researchers are tested. Their paper appeared in a supplement to an August issue of The Bulletin of the American Meteorological Society.
While the authors concluded that there was a 1 in 8 chance of having a decade-long pause in warming like the current plateau, even with rising concentrations of greenhouse gases, the odds of a 15-year pause, they wrote, are only 5 in 100. As a result, the next few years of observations could tip the balance toward further concern or greater optimism.
Meanwhile, social scientists who study the way people understand and respond to environmental problems say it is not surprising that the current temperature stability has created confusion and apathy.
Getting people to care about a climate threat that is decades away is hard enough, they say, without adding in the vagaries of natural climate cycles.
At best, said Robert J. Brulle, a sociologist at Drexel University, global warming remains an abstraction for many people.
“It does not have the direct visual or emotive impact of seeing seabirds covered in oil from the Exxon Valdez oil spill,” he said.
