"Scientists Issue Dire Prediction on Warming" blares the lead headline in the January 23 Washington Post. The earth’s temperature could rise by as much 10.4 degrees Fahrenheit by 2100 and sea levels could rise by 34 inches, warns the Post. The headline and the data derive from the new "Summary for Policymakers," just issued by the United Nation's Intergovernmental Panel on Climate Change (IPCC), which has been meeting in Shanghai. In 1995, the last time the IPCC officially predicted the 21st century’s weather, the maximum projected temperature increase was just 6.3 degrees Fahrenheit. So things must be really heating up fast, right?
Not exactly. "The catastrophic warming projections are based on one set of scenarios that are way off the chart," says John Christy, a professor of Atmospheric Science and director of the Earth System Science Center at the University of Alabama at Huntsville.
The headline-grabbing projected temperature increase comes from the IPCC’s most extreme scenario, out of some 35, that it dreamed up for possible future greenhouse gas emissions. In this ultra-worst-case scenario, a rapidly growing world population merrily burns more and more fossil fuels with virtually no improvement in technology. Then this gloomy econometric forecast is fed into the global climate model most sensitive to perturbations and voila!--cataclysmic catastrophe.
In other words, the prediction that the world might drastically heat up is achieved by combining the outputs from notoriously inaccurate models of economic, demographic, and technological change, and then mixing those results with atmospheric models that are even more fraught with great uncertainties. The last time governments were urged to drastic action by concerned scientists on the basis of computer model results was the Limits to Growth fiasco in the 1970s.
Back then, the Club of Rome solemnly told world leaders that humanity would likely be completely out oil, gas, copper, zinc, gold, and tin by now. If that wasn't bad enough, the Club also said we'd be choking on pollution and experiencing massive famines. President Jimmy Carter commissioned the infamous Global 2000 Report, which seconded the projections made by the limits-to-growth crowd.
Such predictions have been spectacularly wrong: The world has yet to run out of any of these minerals, food has never been cheaper, and pollution levels have been declining in developed countries for three decades. Air pollution is even going down in Mexico City, one of the most heavily polluted cities on the planet.
"The climate models are still not able to reproduce what we’ve seen in the past few decades," says Alabama's Christy. In fact, they predict much more warming than is shown by highly accurate satellite temperature data that's been collected over the past 22 years. The satellites find almost no atmospheric warming, with the earth’s lower atmosphere warming at only about 0.04 degrees Celsius per decade.
The IPCC acknowledges that the satellite data don’t show much warming. It insists, however, that "the global average surface temperature has increased significantly by +0.15 degrees Celsius per decade." The summary then mildly notes that differences between the satellite data and the surface "are not fully resolved." Nevertheless, the IPCC summary boldly claims that "confidence in the ability of the models to project future climate has increased." Such confidence, however is unwarranted. The models predict that the atmosphere’s temperature should be going up more rapidly than the surface temperature. Yet the opposite is occurring.
What could account for the differences in the surface temperature trends and the atmospheric temperature trends? Roger Pielke, Sr., professor of Atmospheric Sciences at Colorado State University, argues that with regard to surface temperatures "land use changes are probably more significant than the radiative effects of doubling carbon dioxide." Pielke believes that the IPCC has misinterpreted increased surface temperatures resulting from land use changes like deforestation, farming, suburbanization, and urbanization, as being changes in atmospheric temperatures caused by increased levels of greenhouse gases. Taking the effects of land use changes into account could explain the discrepancy between the IPCC’s surface temperature data trends and the satellite trends. If that's the case, then increased carbon dioxide levels as a result of burning fossil fuels recedes as a climatological worry.
Pielke also points out that the global climate models do not account for the effects of increased carbon dioxide on plant growth. For example, doubled carbon dioxide levels leads to greater plant growth and improved water-use efficiency. In a grassland model that he ran, the net effect was cooler day-time and warmer night-time temperatures, not apocalypse.
The IPCC summary openly acknowledges that current models can’t account for clouds. This is vital, since clouds act as shades during the day and as blankets at night; they lower daytime temperatures while increasing nighttime ones. The IPCC finds that cloud cover has increased by 2 percent in the last century and that nighttime daily minimum temperatures are going up at twice the rate of daytime high temperatures. What appears to be happening in reality, though not in the models, is that most of the warming over the last few decades is occurring during winter nights. This means that growing seasons are lengthening in the temperate zones, as frosts end earlier in spring and start later in autumn.
"There is clear evidence that we are changing the climate, but we have no idea if the net effect is warming, cooling, moistening, or drying," concludes Pielke.
Despite these vast uncertainties, Klaus Toepfer, head of the U.N. Environment Program, has proclaimed, "The scientific consensus presented in this comprehensive report about human-induced climate change should sound alarm bells in every national capital and every local community."
Adds Robert Watson, chair of the IPCC: "This adds impetus for governments of the world to find ways to live up to their commitments…to reduce emissions in greenhouse gases." Pushing that "impetus" may be the real point of the summary: to scare the bejesus out of skeptical politicians and the public, the better to bring both back to the bargaining table.
Last November, the negotiations at the Hague over the Kyoto Protocol, which sets limits on the levels of greenhouse gases that countries would be permitted to emit by 2010-2012, collapsed. The negotiations fell apart because the Europeans refused to go along with the sensible American point that if one counts everything that adds carbon dioxide to the air, then one should also count things that subtract carbon dioxide from the air, such as forests and farms, which the U.S. has in abundance. Negotiations are slated to resume in Bonn this May, and a few headlines about searing temperatures by the end of the 21st century couldn’t hurt the Protocol's supporters.