Study Predicts Extreme Weather Changes

Scary weather patterns appear to be on the rise. And if a new report is right, we could be in for a lot more. In a study called "Going to the Extremes," coming out in the December issue of the journal Climatic Change, researchers from the National Center for Atmospheric Research (NCAR) and Texas Tech University found strong evidence that by the end of this century, there will be significant increases in what the authors call "extreme weather events"—deadly heat waves, heavy rainfall and prolonged droughts.

While it's impossible to peg any single storm or heat wave to global warming, the overall trend is clear, according to the report—and closely correlated with rising greenhouse-gas emissions. Already we're seeing increases in extreme weather. The study doesn't name examples, but they're not hard to find. There was the heat wave this summer that killed more than 130 people in California. High windstorms in the Southeast this month left a dozen dead and spawned heavy rains and flash flooding up the coast. And the extended drought in Texas has been disastrous for local farmers; as of August, scientists at Texas A&M estimated that it had cost the state $4.1 billion in agricultural losses. "It's the extremes, not the average temperature increases, that cause the most damage to human health, crops, property and infrastructure," says Claudia Tebaldi of NCAR, lead author of the study.

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According to the new report, the precise effects over the coming century will vary by region. The Mediterranean nations and Brazil appear poised for some of the worst droughts and heat spells. But the United States will not escape unscathed. In the Southwest, conditions will be more conducive to drought, while the Northeast will have more heavy rainstorms. The Pacific Northwest will have the worst of both—long dry spells punctuated by sudden downpours. And everyone will suffer dramatically longer, more intense heat waves. Particularly worrisome is the projected increase in hot nights during heat waves, because they tend to be associated with the highest fatality rates. "People get no respite from the heat," explains Tebaldi. The one small bright spot in the report was that growing seasons will lengthen—but that's small consolation to agricultural experts, who say warming will encourage even more weed growth than crop growth. Farmers may have to double or triple their use of herbicides.

Just how drastic will the extremes be? The report doesn't give a single answer, but plots out three alternate pictures of the future. The most optimistic of the scenarios assumes rapid introduction of clean, efficient technologies to reduce greenhouse-gas emissions. The least optimistic shows a future where we more or less muddle along as we are today—but with a much larger population consuming resources. The effects vary accordingly. The numbers defy simple translation into lay language, as they're calculated in what statisticians call "standard deviations"—two standard deviations being the amount of variation you would expect under normal conditions. When variability gets up to four or five standard deviations, that's really big. But consider this: under the worst of the three scenarios, by the year 2099, the length of heat waves will increase by a whopping 12 standard deviations—which is statistician-speak for "holy cow!" "The lengths are so much longer, it's not even on the same scale as today," says Tebaldi.

While global warming studies always have their critics, it's not easy to dismiss these findings. They're based on nine different climate-change models developed by leading scientists in four countries: France, Japan, Russia, and the United States. Each one is processed by supercomputers, crunching millions of data points on variables like surface temperatures, ocean currents, winds, solar radiation, volcanic eruptions and rainforest destruction. Each one takes months to perform. "The fact that all nine produced remarkably consistent agreement gives us a lot of confidence in the results," says Katharine Hayhoe of Texas Tech University, another of the study's authors.

The paper's charts and conclusions are being evaluated by the Intergovernmental Panel on Climate Change for inclusion in its fourth report, due out next spring. The IPCC is a commission established by the United Nations to gather and assess the latest, most authoritative thinking on global warming and its impact around the world on health, agriculture, the economy and other areas. Like the extreme-weather report, the IPCC document will present alternate scenarios for the future, based on how seriously the world tackles the problem. "It's up to us as a whole to make the choices," says Hayhoe. "In a very real way, the future is in our hands." Without concerted effort, she implies, we could all feel the heat.

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