Climate of Opinion

The latest U.N. report shows the "warming" debate is far from settled.

Wall Street Journal

Last week's headlines about the United Nations' latest report on global warming were typically breathless, predicting doom and human damnation like the most fervent religious evangelical. Yet the real news in the fourth assessment from the Intergovernmental Panel on Climate Change (IPCC) may be how far it is backpedaling on some key issues. Beware claims that the science of global warming is settled.

The document that caused such a stir was only a short policy report, a summary of the full scientific report due in May. Written mainly by policymakers (not scientists) who have a stake in the issue, the summary was long on dire predictions. The press reported the bullet points, noting that this latest summary pronounced with more than "90% confidence" that humans have been the main drivers of warming since the 1950s, and that higher temperatures and rising sea levels would result.

More pertinent is the underlying scientific report. And according to people who have seen that draft, it contains startling revisions of previous U.N. predictions. For example, the Center for Science and Public Policy has just released an illuminating analysis written by Lord Christopher Monckton, a one-time adviser to Margaret Thatcher who has become a voice of sanity on global warming.

Take rising sea levels. In its 2001 report, the U.N.'s best high-end estimate of the rise in sea levels by 2100 was three feet. Lord Monckton notes that the upcoming report's high-end best estimate is 17 inches, or half the previous prediction. Similarly, the new report shows that the 2001 assessment had overestimated the human influence on climate change since the Industrial Revolution by at least one-third.

Such reversals (and there are more) are remarkable, given that the IPCC's previous reports, in 1990, 1995 and 2001, have been steadily more urgent in their scientific claims and political tone. It's worth noting that many of the policymakers who tinker with the IPCC reports work for governments that have promoted climate fears as a way of justifying carbon-restriction policies. More skeptical scientists are routinely vetoed from contributing to the panel's work. The Pasteur Institute's Paul Reiter, a malaria expert who thinks global warming would have little impact on the spread of that disease, is one example.

U.N. scientists have relied heavily on computer models to predict future climate change, and these crystal balls are notoriously inaccurate. According to the models, for instance, global temperatures were supposed to have risen in recent years. Yet according to the U.S. National Climate Data Center, the world in 2006 was only 0.03 degrees Celsius warmer than it was in 2001--in the range of measurement error and thus not statistically significant.

The models also predicted that sea levels would rise much faster than they actually have. The models didn't predict the significant cooling the oceans have undergone since 2003--which is the opposite of what you'd expect with global warming. Cooler oceans have also put a damper on claims that global warming is the cause of more frequent or intense hurricanes. The models also failed to predict falling concentrations of methane in the atmosphere, another surprise.

Meanwhile, new scientific evidence keeps challenging previous assumptions. The latest report, for instance, takes greater note of the role of pollutant particles, which are thought to reflect sunlight back to space, supplying a cooling effect. More scientists are also studying the effect of solar activity on climate, and some believe it alone is responsible for recent warming.

All this appears to be resulting in a more cautious scientific approach, which is largely good news. We're told that the upcoming report is also missing any reference to the infamous "hockey stick," a study by Michael Mann that purported to show 900 years of minor fluctuations in temperature, followed by a dramatic spike over the past century. The IPCC featured the graph in 2001, but it has since been widely rebutted.

While everyone concedes that the Earth is about a degree Celsius warmer than it was a century ago, the debate continues over the cause and consequences. We don't deny that carbon emissions may play a role, but we don't believe that the case is sufficiently proven to justify a revolution in global energy use. The economic dislocations of such an abrupt policy change could be far more severe than warming itself, especially if it reduces the growth and innovation that would help the world cope with, say, rising sea levels. There are also other problems--AIDS, malaria and clean drinking water, for example--whose claims on scarce resources are at least as urgent as climate change.

The IPCC report should be understood as one more contribution to the warming debate, not some definitive last word that justifies radical policy change. It can be hard to keep one's head when everyone else is predicting the Apocalypse, but that's all the more reason to keep cool and focus on the actual science.