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Climate change is wild card as tornado seasons smash records

No place on earth creates as many tornadoes as the southern and central United States.  And here in the global heartland of tornadoes the last few years have whip lashed between record breaking extremes. Along the way the three most damaging  tornadoes in world history plowed multi-billion dollar swaths of death and destruction through the American cities of Joplin, Tuscaloosa and Moore.

Record breaking tornado years

The best source on climate change and tornadoes that I've found is the writings of  meteorologist Dr. Jeff Masters. He tells the tale of the recent remarkable whiplash between extremes:

"In May 2011, the Joplin, Missouri tornado did $3 billion in damage--the most expensive tornado in world history--and killed 158 people, the largest death toll from a U.S. tornado since 1947.

An astounding 1050 EF-1 and stronger tornadoes ripped though the U.S. for the one-year period ending that month. This was the greatest 12-month total for these stronger tornadoes in the historical record, and an event so rare that we might expect it to occur only once every 62,500 years.

Fast forward now to May 2012 - April 2013 … the lowest 12-month total of EF-1 and stronger tornadoes on record--just 197. This was an event so rare we might expect it to occur only once every 3,000 - 4,000 years."

Here's a chart I made of these unprecedented extremes:

click to view larger... 

The world's three most damaging tornadoes

My chart also shows the three most damaging tornadoes in world history. These are the only tornadoes to ever cause $2 billion or more in damages (in 2013 dollars):

#1 May 22, 2011 in Joplin, Missouri

 

#2 April 27, 2011 in Tuscaloosa, Alabama

 

#3 May 20, 2013 in Moore, Oklahoma

 

The world's seventh most damaging tornado of all time hit Hackleburg, Alabama on the same day as the Tuscaloosa twister. These were part of an epic four day "Super Outbreak" of multiple tornadoes that broke all damage records with combined damage surpassing $10 billion.

The climate change wildcard

Clearly the recent tornado weather is far from normal. The critical question is how is climate change affecting tornadoes -- now and into the future?

Will our ever increasing emissions of fossil fuel pollution fuel an ever increasing level of extreme tornado weather, like it has been doing with extreme rainfall, flooding, heat waves, drought, ice melt and the most powerful hurricanes?

The answer is unsettling: nobody knows.

Even more unsettling to me is that we probably won't know for a long time.

Here is what we do know about how our climate pollution is affecting two of the critical ingredients of tornadoes:

1)    MORE WATER VAPOUR. Water vapour is the "gasoline" powering tornadoes, thunderstorms, extreme rainfall and hurricanes. As water vapour condenses into water droplets (clouds and rain) a tremendous amount of heat is released. It is that heat that provides much of the power of these storms. We know that climate change has significantly increased the amount of water vapour in the atmosphere, making more "fuel" available to storms.

2)    ALTERED JET STREAM. The jet stream plays a major role in the upper atmospheric wind and moisture conditions required to start tornadoes spinning and keep them spinning. We know that climate change has weakened and stretched the jet stream over North America.

What we don't know is how climate changes such as these affect the number or power of tornadoes.

The reason we don't know is because we have very poor records of past tornadoes. If you don't know what happened in the past you can't say if the present situation is different.

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