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June 5, 2011

Experts: Strange weather largely cyclical, not a trend

— People in the South have long been known to talk about the weather as a casual greeting or icebreaker but since last summer, when the temperature climbed to 106 degrees, weather is serious business.

After the record-breaking temperatures of 2010, Limestone County residents experienced the first white Christmas in 21 years, followed by a debilitating snowstorm in January. But spring’s weather has sparked the most discussions, with the April 27 tornado outbreak smashing records.

And weather hasn’t only been a phenomenon here: record-breaking blizzards in the northeast in winter, tornado outbreaks in Joplin, Mo., and unusual occurrences of tornadoes in California and Massachusetts. In July 2010, a world record-setting hailstone — 8 inches in diameter and 1.94 pounds — fell on Vivian, S.D.

According to the National Oceanic and Atmospheric Administration, the U.S. has sustained 99 weather-related disasters over the past 31 years in which overall costs reached or exceeded $1 billion, with a total of those events reaching $725 billion. The April 27 tornado outbreak is expected to cost Alabama about $4 billion.

Is climate change occurring?

Many people are asking, “Is weather becoming more severe?” Are the extreme conditions a trend expected to last, or are they part of normal cyclical weather patterns?

Chris Darden, head meteorologist with the National Weather Service in Huntsville, believes the extreme weather the area has experienced in the past year is the result of typical cycles that may be impacted by the El Nino, La Nina phenomenon.

El Niño-Southern Oscillation, or ENSO, is a climate pattern that occurs about every five years across the tropical Pacific Ocean. A warming in the temperature of the surface of the ocean is known as El Niño, while a cooling is called La Niña.

Darden, however, said scientists disagree.

“The jury’s still out,” he said. “Some researchers feel that El Niño, La Niña have something to do with the increased severity of weather. We experienced El Niño last year, which changed over to La Niña over the winter and into this year.”

There is evidence, though, that the recent severe weather is cyclical.

“A lot of people who do this research think the severe weather outbreaks, not just here but across the country, is part of a multi-detailed cycle,” Darden said. “The last big tornado outbreak was in 1974, with quite a few weather events preceding it in the early 1970s. If you do the numbers, it occurs about every 40 years.”

Some Limestone Countians have witnessed this cycle themselves. Jean Bond lost her home on Stewart Road in Tanner in the 1974 Super Outbreak. It was destroyed again on April 27.  But Bond said she plans to rebuild: “If they’re coming every 37 years, I won’t be here,” said the 70-something Bond.

Despite recent focus on global warming, these extremes are naturally occurring and not manmade, said John R. Christy, distinguished professor of atmospheric science, Alabama’s state climatologist and director of the Earth System Science Center at the University of Alabama in Huntsville.

“Recently it has become popular to try and attribute certain extreme events to human causation,” Christy said. “The Earth, however, is very large, the weather is very dynamic, especially at local scales, so that extreme events of one type or another will occur somewhere on the planet in every year. Since there are innumerable ways to define an extreme event (i.e. record high and low temperatures, number of days of a certain quantity, precipitation over 1, 2, 10 days, snowfall amounts, etc.) this essentially requires there to be numerous ‘extreme events’ in every year.”

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