By David Fahrenthold and Juliet Eilperin
With its 2007 report declaring that the "warming of the climate system is unequivocal", the UN Intergovernmental Panel on Climate Change (IPCC) won a Nobel Prize - and a new degree of public trust in the controversial science of global warming.
But recent revelations about flaws in that seminal report, ranging from typos in key dates to sloppy sourcing, are undermining confidence not only in the panel's work but in projections about climate change.
Scientists who have pointed out problems in the report say the panel's methods and mistakes - including admitting at the weekend that it had overstated how much of the Netherlands was below sea level - give doubters an opening.
It wasn't the first one. There is still a scientific consensus that humans are causing climate change. But in the past year, a cache of stolen emails, revealing that prominent climate scientists sought to keep their critics from publication, has sullied their image as impartial academics.
The errors in the UN report - a document intended to be the last nail in the coffin of climate doubt - are a serious problem that could end up forcing environmentalists to focus more on the old question of proving climate change is a threat, instead of the new question of how to stop it.
Two US Republican senators who have long opposed a cap on carbon emissions, James Inhofe, of Oklahoma, and John Barrasso, of Wyoming, are citing the errors as further reasons to block mandatory limits on greenhouse gas emissions.
Last week, Barrasso called for an independent probe of the IPCC, suggesting that the US should halt any action on climate until it verifies the panel's scientific conclusions.
Inhofe said in the Senate that the efforts of the Environmental Protection Agency (EPA) to curb greenhouse gases should be re-examined, as the UN panel's conclusions influenced the agency's finding that climate change poses a public threat.
"There is a sense that something's rotten in the state of the IPCC," said Richard Moss, a senior scientist at the Joint Global Change Research Institute at the University of Maryland, who has worked with the panel since 1993.
"It's just wildly exaggerated. But we need to take a look and see if something needs to be improved."
The IPCC climate assessments are a massive undertaking.
Thousands of scientists across the globe volunteer to evaluate tens of thousands of academic documents and translate them into plain-English reports that policymakers can understand.
Climate researchers say the errors do not disprove the UN panel's central conclusion: climate change is happening, and humans are causing it.
Some researchers said the UN panel's attitude - appearing to promise that its results were infallible, and reacting slowly to evidence that they were not - could undermine the rest of its work.
"What's happened here is that there's an industry of climate change denialists who are trying to make it seem as though you can't trust anything that is between the covers" of the panel's report, said Jeffrey Kargel, a professor at the University of Arizona who studies glaciers.
"It's really heartbreaking to see this happen, and to see that the IPCC left themselves open (to being attacked)."
Kargel said he noticed an error in the report of the IPCC's second working group, a research unit, in 2007.
The report said huge glaciers in the Himalayan mountains might disappear by 2035.
Some glaciers are melting, but they are too enormous to disappear that quickly: "It's physically impossible to kill the ice that fast," Kargel said. He said colleagues regarded the error as too ridiculous to fuss about until recently, when the journal Science printed a letter to the editor that traced the origins of the mistaken data: the UN panel seemed to have quoted an activist group's report, not a peer-reviewed study. And, in citing another source, it appeared to have committed a serious typo: the year had become 2035.
Another line that has sparked scrutiny reads, "Up to 40 percent of the Amazonian forests could react drastically to even a slight reduction in precipitation", and links to a report co-written by the World Wide Fund for Nature.
The analysis cited key work by Woods Hole Research Centre senior scientist Daniel Nepstad, but the link to an advocacy group instead of a peer-reviewed paper infuriated conservatives.
"The underlying science is certainly there, but the citation process the IPCC went through is sloppy," said Doug Boucher, director of the Tropical Forest and Climate Initiative at the Union of Concerned Scientists.
Roger Pielke jr, a political scientist and environmental studies professor at the University of Colorado, said the UN panel could hurt its own public standing by not admitting how it exaggerated certain climate risks or connections, such as linking higher insurance payouts to rising temperatures when other factors are driving this trend. - The Washington Post