Hot New Report on Climate Change.

At a January 2001 meeting in Shanghai, China, the United States and other members of the Intergovernmental Panel on Climate Change (IPCC) agreed that human activities are the likely cause of most of the global warming that has occurred in the last 50 years. They also predicted a 1.4-5.8 [degrees] C (2.5-10.4 [degrees] F) increase in global average surface temperatures between 1990 and 2100. The specific use of "likely" reflects the panel's judgment that its conclusion has a 66-90% chance of accuracy. That finding is considerably more forceful than a similar assessment completed in 1995 in which the IPCC reported that evidence suggested a "discernible human influence" on global climate.

The IPCC works to assess human impacts on the global climate, the potential effects of climate change, and options for mitigating those effects through the efforts of three separate working groups, which primarily review existing literature and data. Collectively, the working groups have produced two assessment reports, the most recent in 1995. The report of Working Group I will be combined with findings from the other two groups into a report to be presented in September 2001.

In Shanghai, IPCC members unanimously approved a summary for policy makers that highlights key findings of Working Group I, a panel of hundreds of scientists charged with assessing the scientific basis for human-induced climate change. The summary of the Working Group I report cites a 0.6 [degrees] C ([+ or -] 0.2 [degrees] C) increase in the global average surface temperature over the twentieth century, which is approximately 0.15 [degrees] C higher than was estimated in 1995. Because of improved ability to reconstruct historical meteorologic data and through factoring in the relatively high temperatures of 1995-2000, Working Group I was able to assert that it is likely that the 1990s was the warmest decade and 1998 the warmest year in the last 1,000 years in the Northern Hemisphere. The summary also cites a "very likely" (90-99% probability) decrease in lake and river ice in parts of the Northern Hemisphere and widespread retreat of mountain glaciers in nonpolar regions during the twentieth century. Additionally, a 0.1-0.2 meter increase in the global average sea level is also likely to have occurred during that time.

The extent of warming since the 1950s was unprecedented and unlikely to be entirely natural in origin, according to the summary. Moreover, the summary predicts that warming will very likely persist into the twenty-first century, producing higher maximum and minimum temperatures, fewer cold days, and fewer frost days over nearly all land areas, along with an increased risk of drought over most mid-latitude continental interiors.

Such projections are based on computer models that have improved since 1995, according to David Griggs, a meteorology and climate scientist who heads Working Group I's Technical Support Unit. And, although every step of the modeling process has uncertainties, he says, those uncertainties are factored in to the level of confidence with which assertions are made and are reflected in the ranges of possible effects.

John Christy, a professor of atmospheric science at the University of Alabama in Huntsville and a lead author of the Working Group I report, believes the uncertainties limit the report's usefulness for policy makers. Computer models suggest that if humans are inducing climate change, tropospheric temperatures would warm along with surface temperatures, says Christy. Yet satellite data indicate that tropospheric temperatures have warmed much more slowly than surface temperatures in the last 22 years. Although Christy says the inconsistency does not refute a conclusion that humans are inducing warming, he believes it indicates that the report may not make a fully reliable basis for policy making.

Others believe the report will be a useful tool. Bill Hare, climate policy director for Greenpeace International, thinks the report will put pressure on countries such as the United States to achieve previously agreed upon emissions limits. (The Bush administration nevertheless still strongly opposes the Kyoto Protocol. In a 28 March 2001 news briefing, press secretary Ari Fleischer said, "The president has been unequivocal--he does not support the Kyoto treaty. It exempts the developing nations around the world, and it is not in the United States' economic best interest.") But Hare also believes the summary understates the risks associated with human impacts on climate. "[IPCC members] focused on writing down everything that could be agreed upon among everyone, and hence the summary is a lowest-common-denominator statement," he says. Consequently, the summary "hasn't presented the worst-case [scenario], or even what risks are likely to happen."