COPENHAGEN — Just two years ago, a United Nations panel that synthesizes the work of hundreds of climatologists around the world called the evidence for global warming “unequivocal.”
But as representatives of about 200 nations began talks Monday in Copenhagen on a new international climate accord, they were doing so against a background of renewed attacks on the basic science of climate change.
The debate, set off by the circulation of several thousand files and e-mail messages stolen from one of the world’s foremost climate research institutes, has led some who oppose limits on greenhouse gas emissions, and at least one influential country, Saudi Arabia, to question the scientific basis for the Copenhagen talks.
The uproar has threatened to complicate a multiyear diplomatic effort already ensnared in difficult political, technical and financial disputes that have caused leaders to abandon hopes of hammering out a binding international climate treaty this year.
In recent days, an array of scientists and policy makers have said that nothing so far disclosed — the correspondence and documents include references by prominent climate scientists to deleting potentially embarrassing e-mail messages, keeping papers by competing scientists from publication and making adjustments in research data — undercuts decades of peer-reviewed science.
Yet the intensity of the response highlights that skepticism about global warming persists, even as many scientists thought the battle over the reality of human-driven climate change was finally behind them.
On dozens of Web sites and blogs, skeptics and foes of greenhouse gas restrictions take daily aim at the scientific arguments for human-driven climate change. The stolen material was quickly seized upon for the questions it raised about the accessibility of raw data to outsiders and whether some data had been manipulated.
An investigation into the stolen files is being conducted by the University of East Anglia, in England, where the computer breach occurred. Rajendra K. Pachauri, chairman of the United Nations Intergovernmental Panel on Climate Change, has also said he will look into the matter. At the same time, polls in the United States and Britain suggest that the number of people who doubt that global warming is dangerous or caused by humans has grown in recent years.
Politics, ideology and economic interests interlace the debate, and the stakes on both sides are high. If scientific predictions about global warming’s effects are correct, inaction will lead at best to rising social, economic and environmental disruption, at worst to a calamity far more severe. If the forecasts are wrong, nations could divert hundreds of billions of dollars to curb greenhouse gas emissions at a time when they are struggling to recover from a global recession.
Yet the case for human-driven warming, many scientists say, is far clearer now than a decade ago, when the skeptics included many people who now are convinced that climate change is a real and serious threat.
Even some who remain skeptical about the extent or pace of global warming say that the premise underlying the Copenhagen talks is solid: that warming is to some extent driven by greenhouse gases spewing into the atmosphere from human activities like the burning of fossil fuels and deforestation.
Roger A. Pielke Sr., for example, a climate scientist at the University of Colorado who has been highly critical of the United Nations climate panel and who once branded many of the scientists now embroiled in the e-mail controversy part of a climate “oligarchy,” said that so many independent measures existed to show unusual warming taking place that there was no real dispute about it. Moreover, he said, “The role of added carbon dioxide as a major contributor in climate change has been firmly established.”
The Copenhagen conference itself reflects increasing acceptance of the scientific arguments: the negotiations leading to the talks were conducted by high-ranking officials of the world’s governments rather than the scientists and environment ministers who largely shaped the 1997 Kyoto Protocol. Late last week, President Obama changed the date of his visit to Copenhagen to Dec. 18, the last day of the talks.
For many, a 2007 report by the Intergovernmental Panel on Climate Change was a marker of a shift in the global warming debate. In it, the panel — a volunteer network of hundreds of scientists from many disciplines who meet periodically to review climate studies and translate the results into language useful to policy makers — concluded that no doubt remained that human-caused warming was under way and that, if unabated, it would pose rising risks.
Over the last several decades, other reviews, by the National Academy of Sciences and other institutions, have largely echoed the panel’s findings and said the remaining uncertainties should not be an excuse for inaction.
The panel’s report was built on two decades of intensive scientific study of climate patterns.
Greenhouse gases warm the planet by letting in sunlight and blocking the escape of some of the resulting heat. “The physics of the greenhouse effect is so basic that instead of asking whether it would happen, it makes more sense to ask what on earth could make it not happen,” said Spencer Weart, a physicist and historian. “So far, nobody has been able to come up with anything plausible in that line.”
The atmospheric concentration of greenhouse gases released by humans has risen rapidly in the last century, along with industrialization and electricity use. Carbon dioxide from burning of coal, oil and natural gas is the most potent of the greenhouse gases because it can persist in the atmosphere for a century or more.、
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