IT'S NOT quite the hurricane-force blow to skeptics of global warming that many climatologists would have preferred, but for a document drafted by hundreds of scientists representing 113 governments, the latest report from the United Nations Intergovernmental Panel on Climate Change, released Friday, is nevertheless full of frightening evidence and, we hope, policy-inducing conclusions.
Here are some of the more notable conclusions: There is no doubt that the planet is warming, according to all sorts of measures, from rising air and ocean temperatures to widespread melting of snow and ice. Increases in global temperature are "very likely" the result of higher concentrations of greenhouse gases, which are far higher now than they have been over the past 650,000 years. Policymakers should expect global temperatures to continue to rise, even if greenhouse gas concentrations stay at the levels of the year 2000. Continuing to release greenhouse gases at current rates would warm the Earth even more and would be "very likely" to yield much more severe consequences during this century than those we saw in the previous one. Sea levels will rise, heat waves and droughts will strike longer and more often, hurricanes will become more intense, and it will rain more in high latitudes.
Many climate scientists say the report doesn't go far enough. Michael Mann, a leading climatologist at Pennsylvania State University, welcomes the assessment, but he says that it probably underestimates how high oceans could rise over the next century or so, especially if the ice covering Greenland melts faster than expected. He may be right: Recent research on melting ice caps suggests that cracks in the ice will speed up the melting process.
The assessment's value does not lie in its innovative approach to describing global climate change. On the contrary, because so many individuals and organizations signed on, the report's strong language is virtually unassailable. Even the Bush administration hailed it, which makes the president's continued neglect of the issue particularly troubling. Now that leaders in the United States and abroad have agreed on the basics of the problem and the seriousness of the consequences, sound policy -- the likes of which President Bush continues to oppose -- should follow.