Could a warming planet change tornado season, too? Scientists seek clues

These unpredictable, sometimes deadly storms plague the United States more than any other country. Here in tornado alley, Oklahoma City has been hit with at least 147 tornadoes since 1890.

But as the traditional tornado season nears, scientists have been pondering a simple question: Will there be more or fewer twisters as global warming increases?

There is no easy answer. Lately, tornado activity in America has been Jekyll-and-Hyde weird, and scientists are unsure if climate change has played a role in recent erratic patterns.

In 2011, the United States saw its second-deadliest tornado season in history: Nearly 1,700 tornadoes killed 553 people. The Joplin, Missouri, twister was the single deadliest in American history, killing 158 people and causing US$2.8 billion in damage.

The following year, 2012, started even earlier and even busier. Through April there were twice as many tornadoes as normal. Then the twisters suddenly disappeared. Tornado activity from May to August of that year was the lowest in 60 years of record-keeping, said Harold Brooks, a top researcher at the National Weather Center.

Meanwhile, Canada saw an unusual number of tornadoes in 2012; Saskatchewan had three times the normal number.

That year, the jet stream moved north and “essentially shut down” tornadoes in the American Midwest said Greg Carbin, warning meteorologist at the federal storm center. A tremendous drought meant far fewer storms, which not only shut off the spigot on rain but on storm cells that spawned tornadoes.

For much of America, tornadoes are seasonal. Typically, there are more during spring, and the numbers dwindle in the worst heat of the summer. Last year “essentially was an extended period of summertime conditions over the U.S.,” Carbin said. “The real question is: What is spring now? Is it February?”

“Summer may be happening earlier and may be muscling out what we consider a transition between summer and winter,” he said.

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