TORNADO Joplin, Mo., suffered severe damage in May. Scientists say data suggest an increase in tornadoes as the climate warms, but no rigorous analyses have been conducted.
At the end of one of the most bizarre weather years in American history, climate research stands at a crossroads.
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Kiichiro Sato/Associated Press
BLIZZARD A severe storm hobbled Chicago in February.
Scientists say they could, in theory, do a much better job of answering the question “Did global warming have anything to do with it?” after extreme weather events like the drought in Texas and the floods in New England.
But for many reasons, efforts to put out prompt reports on the causes of extreme weather are essentially languishing. Chief among the difficulties that scientists face: the political environment for new climate-science initiatives has turned hostile, and with the federal budget crisis, money is tight.
And so, as the weather becomes more erratic by the year, the public is left to wonder what is going on.
When 2010 ended, it seemed as if people had lived through a startling year of weather extremes. But in the United States, if not elsewhere, 2011 has surpassed that.
A typical year in this country features three or four weather disasters whose costs exceed $1 billion each. But this year, the National Oceanic and Atmospheric Administration has tallied a dozen such events, including wildfires in the Southwest, floods in multiple regions of the country and a deadly spring tornado season. And the agency has not finished counting. The final costs are certain to exceed $50 billion.
“I’ve been a meteorologist 30 years and never seen a year that comes close to matching 2011 for the number of astounding, extreme weather events,” Jeffrey Masters, a co-founder of the popular Web site Weather Underground, said last month. “Looking back in the historical record, which goes back to the late 1800s, I can’t find anything that compares, either.”
Many of the individual events in 2011 do have precedents in the historical record. And the nation’s climate has featured other concentrated periods of extreme weather, including severe cold snaps in the early 20th century and devastating droughts and heat waves in the Dust Bowl era of the 1930s.
But it is unusual, if not unprecedented, for so many extremes to occur in such a short span. The calamities in 2011 included wildfires that scorched millions of acres, extreme flooding in the Upper Midwest and the Mississippi River Valley and heat waves that shattered records in many parts of the country. Abroad, massive floods inundated Australia, the Philippines and large parts of Southeast Asia.
A major question nowadays is whether the frequency of particular weather extremes is being affected by human-induced climate change.
Climate science already offers some insight. Researchers have proved that the temperature of the earth’s surface is rising, and they are virtually certain that the human release of greenhouse gases, mainly from the burning of fossil fuels, is the major reason. For decades, they have predicted that this would lead to changes in the frequency of extreme weather events, and statistics show that has begun to happen.
For instance, scientists have long expected that a warming atmosphere would result in fewer extremes of low temperature and more extremes of high temperature. In fact, research shows that about two record highs are being set in the United States for every record low, and similar trends can be detected in other parts of the world.
Likewise, a well-understood physical law suggests that a warming atmosphere should hold more moisture. Scientists have directly measured the moisture in the air and confirmed that it is rising, supplying the fuel for heavier rains, snowfalls and other types of storms.
“We are changing the large-scale properties of the atmosphere — we know that beyond a shadow of a doubt,” said Benjamin D. Santer, a leading climate scientist who works at the Lawrence Livermore National Laboratory in California. “You can’t engage in this vast planetary experiment — warming the surface, warming the atmosphere, moistening the atmosphere — and have no impact on the frequency and duration of extreme events.”
But if the human contribution to heat and precipitation is clear, scientists are on shakier ground analyzing many other events. Tornadoes, the deadliest weather disaster to hit the country this year, present a particularly thorny case.
On their face, weather statistics suggest that tornadoes are becoming more numerous as the climate warms. But tornadoes are small and hard to count, and scientists have little confidence in the accuracy of older data, which means they do not know whether to believe the apparent increase. Likewise, the computer programs they use to analyze and forecast the climate do not do a good job of representing events as small as tornadoes.
Some scientists have offered theories about how increasing heat and moisture may have made tornado outbreaks more likely, but these have not yet been tested in rigorous analyses. Many other types of extreme weather fall into this category, with scientists lacking a strong basis for attributing increases to human activity, or for discounting a human effect.
The question can sometimes be answered with focused studies of a specific weather event, but these are often finished years afterward. Lately, scientists have been discussing whether they can do a better job of analyzing events within days or weeks, not years.
“It’s clear we do have the scientific tools and the statistical wherewithal to begin answering these types of questions,” Dr. Santer said.