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Should Recent Extreme Weather Be Tied to Climate Change?

Teasing out the links—or lack thereof—between extreme weather events from droughts to storms has proved difficult for scientists
drought, weather, extreme weather, climate change, global warming



Flickr/steven_schroeder

BOSTON—If droughts, floods and wildfires are the criminal, climate change is the accomplice.

This is how the population must begin regarding global warming, experts said at a session at the annual American Academy for the Advancement of Science meeting here. Although extreme weather events, from the creeping drought that scorched last year's corn crop to Superstorm Sandy, are worrisome, automatically and simplistically tying them to the scientific phenomenon of climate change could be misleading.

Last year's drought in Texas, for example, could not be specifically tied to climate change, said John Nielsen-Gammon, the Lone Star State's climatologist. Over the past century there has been an increase in rainfall -- not a tendency toward dryness -- over most of Texas by about 10 percent.

"Changing climate has not contributed to the lack of rainfall over the long term, as of yet," he said. Last year's drought, much like the famed Dust Bowl drought of the 1930s and another significant drought in the 1950s, is tied to rising sea surface temperatures in the Pacific Ocean -- the weather event known as la Niña.

"Until we see a long-term decrease in rainfall in Texas, it will be hard to say that climate change has caused a decrease," Nielsen-Gammon said.

Temperatures have risen in Texas, meaning the increased rainfall is being evaporated at a more rapid rate, he added. But for the drought, which continues to seize more than half of the lower 48 states, heat was a drought accelerant but not the main cause.

All weather seems suspicious
The strong link to past events divorces the drought from climate. As climate scientists strive to educate the public, not tying a weather event to climate change is proving to be just as difficult as showcasing droughts and hurricanes as examples.

"All weather seems suspicious now," said Andrew Freedman, a senior science writer with Climate Central. The Thailand floods of 2011 are another example of a weather event with a tangential tie to climate. The devastation was more of a cause of poor management than anything else. The blizzard that hit the Northeast earlier this month was, despite dropping a tremendous amount of precipitation in 24 hours, nothing more than a strong nor'easter, according to Freedman.

"We see that, it looked like a nor'easter on satellite, it talked like a nor'easter," he said. "A lot of the climate discussion I thought was off-base."

La Niña and its weather brother, El Niño, are atmospheric events triggered by changes in surface sea level temperatures. The current drought was characterized by cold sea surface temperatures in the tropical Pacific Ocean, said Richard Seager, a research professor at the Lamont-Doherty Earth Observatory at Columbia University.

Sea surface temperature has a strong control on precipitation and soil moisture, said Seager, who compared the 2011 and 2012 droughts to the 20th century's other major droughts across the central United States.

Extending normal drought patterns
By using tree ring records to study ancient climates, David Stahle, a professor of geosciences at the University of Arkansas, found patterns between the recent droughts and the Great Pueblo Drought of the 13th century in the region across Colorado, New Mexico, Utah and Arizona.

"What's worrisome is that the escalation of temperature may cause these kinds of normal-occurring drought patterns to be more intense and prolonged," he said.

Poor soil management during the Dust Bowl is another factor to consider. The overtilling and poor nurturing of soils led to massive dust clouds and exacerbated the drought in the 1930s. Dust creates an energy sink by absorbing solar radiation, Seager said. Today, advances in agriculture have greatly controlled that problem.

The La Niña pattern of droughts may not hold true forever, Seager added. As climate change alters atmospheric circulation, it will do the same to age-old assumptions. Crop failures and dust storms are shifting northward compared with the 1930s drought.

"In the past, we've always had these droughts, we know now in recent years they're related to tropical sea surface temperature anomalies," Seager said. "The fact is, things do seem to be evolving the way we would expect them to be [with climate change], and if that is so, in key regions in the Southwest such as California and the Colorado [River] headwaters, there will be a notable and appreciable reduction in soil moisture within the near-term future, the next two decades or so."

The panel also included Donald Wuebbles, a professor of atmospheric sciences at the University of Illinois, Urbana-Champaign, and Camille Parmesan, a professor of integrative biology at the University of Texas, Austin.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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