In its 2007 report on the effects of global warming, the Intergovernmental Panel on Climate Change stated that glaciers could vanish from the Himalayas by 2035. As has since been widely reported, with ill-disguised glee by many blogs and right-wing news outlets, this was a blunder. The prediction didn't come from a peer-reviewed scientific study but from a prominent Indian glacier expert who was quoted in a British popular science magazine -- and who now claims he never gave such a date.
This wasn't the only error in the report, which has been a key justification of international efforts to fight climate change. It also claimed that 55% of the Netherlands is below sea level; actually, it's only 26% (the number came from the Dutch government, which has acknowledged its error). Other mistakes have been alleged, and it would be surprising if more weren't found, given that the report runs to 3,000 pages and attempts to summarize peer-reviewed studies and other complex evidence submitted by thousands of scientists around the world.
Except for the glaring glacier mistake, most of the alleged errors are minor, and some may not be errors at all. A controversial claim that up to 40% of the Amazon rain forest could react drastically to even slight reductions in precipitation apparently came from a World Wildlife Fund report rather than a peer-reviewed study, but a leading Amazon researcher has since affirmed that the number is correct. Still, the fact that reports from popular science magazines and environmental advocacy groups could have found their way into a document of such magnitude suggests that the IPCC isn't living up to its own standards. So we applaud the panel's announcement that it is appointing an independent committee to investigate the matter and ensure adherence to scientific procedures.