MORE than 600 self-confessed climate sceptics met in a Times Square hotel in New York this month to challenge what has become a broad scientific and political consensus: that without big changes in energy choices, humans will dangerously heat up the planet.
The three-day International Conference on Climate Change – organised by the Heartland Institute, a nonprofit group seeking deregulation and unfettered markets – brought together political figures, conservative campaigners, scientists, an Apollo astronaut and the President of the Czech Republic, Vaclav Klaus.
Organisers say the discussions were intended to counter the Obama administration and Democratic lawmakers who have pledged to tackle global warming with legislation requiring cuts in the greenhouse gases that scientists have linked to rising temperatures.
The participants hold a wide range of views on climate science. Some concede that humans probably contribute to global warming, but they argue that the shift in temperatures poses no urgent risk.
Others attribute the warming, along with cooler temperatures in recent years, to solar changes or ocean cycles.
But large corporations such as Exxon Mobil, which in the past financed the Heartland Institute and other groups that challenged the climate consensus, have reduced support. Many such companies no longer dispute that the greenhouse gases produced by burning fossil fuels pose risks.
From 1998 to 2006, Exxon Mobil, for example, contributed more than $600,000 (414,000) to Heartland, according to annual reports of charitable contributions from the company and company foundations.
Alan Jeffers, a spokesman for Exxon Mobil, said by e-mail that the company had ended support "to several public policy research groups whose position on climate change could divert attention from the important discussion about how the world will secure the energy required for economic growth in an environmentally responsible manner".
Joseph Bast, the president of the Heartland Institute, said that Exxon and other companies were just shifting their stance to improve their image. The Heartland meeting, he said, was the last bastion of intellectual honesty on the climate issue.
"Major corporations are painting themselves green around global warming," Bast said, adding that the companies have shifted their lobbying and public relations efforts toward trying to shape climate legislation in their favour. He said that contributions overall had continued to rise.
But Kert Davies, a climate campaigner for Greenpeace, said that the experts giving talks were "a shrinking collection of extremists" and that they were "left talking to themselves".
Organisers point to the speaker's roster, which included Klaus and Harrison Schmitt, a geologist, Apollo astronaut and former senator.
A centrepiece of the 2008 meeting was the release of a report, 'Nature, Not Human Activity, Rules The Planet'. The document was expressly designed as a challenge to the reports from the UN Intergovernmental Panel on Climate Change.
This year the meeting focused on a more nuanced question: "Global warming: Was it ever a crisis?"
Some, including prominent figures who have been vocal in their criticism in the past, called on their colleagues to synchronise the arguments they are using against plans to curb greenhouse gases.
Richard Lindzen, a professor at MIT and a longtime sceptic of the mainstream consensus that global warming poses a danger, first delivered a biting attack on what he called the "climate alarm movement".
There is no solid scientific evidence to back up the models used by climate scientists who warn of dire consequences if warming continues, he said. But Lindzen also criticised widely publicised assertions by other sceptics that variations in the sun were driving temperature changes in recent decades. To attribute short-term variation in temperatures to a single cause, whether human-generated gases or something else, was erroneous, he said.
Speaking of the sun's slight variability, he said: "Acting as though this is the alternative (to blaming greenhouse gases] is asking for trouble."
S Fred Singer, a physicist often referred to by critics and supporters alike as the dean of climate contrarians, said: "As a physicist, I am concerned that some sceptics, a very few, are ignoring the physical basis.
"There is one who denies that CO2 is a greenhouse gas, which goes against actual data," Singer said, adding that other sceptics wrongly contend that "humans are not responsible for the measured increase in atmospheric CO2."
There were notable absences from the conference this year. Russell Seitz, a physicist from Cambridge, Massachusetts, delivered a speech at last year's meeting. But Seitz, who has lambasted environmental campaigners for distorting climate science, now warns that the sceptics are in danger of doing the same thing.
The most strident advocates on either side of the global warming debate, he said, are "equally oblivious to the data they seek to discount or dramatise".
John Christy, an atmospheric scientist at the University of Alabama who has long publicly questioned projections of dangerous global warming, most recently at a House committee hearing last month, said he had skipped both Heartland conferences to avoid the potential for "guilt by association".
Many participants said that any division or dissent was minor and that the global recession and a series of years with cooler temperatures would help them in combating changes in energy policy in Washington.
"The only place where this alleged climate catastrophe is happening is in the virtual world of computer models, not in the real world," said Marc Morano, a speaker at the meeting and a spokesman on environmental issues for Republican senator James Inhofe.
But several climate scientists who are seeking to curb greenhouse gases strongly criticised the meeting.
Stephen Schneider, a climatologist at Stanford University and an author of many reports by the Intergovernmental Panel on Climate Change, said, after reviewing the text of presentations for the Heartland meeting, that they were efforts to "bamboozle the innocent".
Yvo de Boer, head of the UN office running the meetings leading to a new global climate treaty, to be signed in December in Copenhagen, said: "I don't believe that what the sceptics say should provide any excuse to delay further action against global warming."
But he added: "Sceptics are good. It's important to give people the confidence that the issue is being called into question."