The complicated science of tornadoes and climate

4-27-11 Tornado Tuscaloosa, Al from Crimson Tide Productions on Vimeo.

Is the number of tornadoes that happens every year going up? And, if so, is it a climate change thing? A natural variation? A little of both? Over at Time, Ecocentric writer Bryan Walsh digs into the complicated reality behind the inevitable questions.

What we really want to know is: did climate change play a role in the monster tornadoes of April, and will a warming world see more destructive cyclones like these? (I know this because my editor, as he's wont to do after major weather events, walked down to my office and asked me, "Bryan, does climate change play a role in this?")

Scientists really don't know. It's true that the average number of April tornadoes has steadily increased from 74 a year in the 1950s to 163 a year in the 2000s. But most of that increase, as A.G. Sulzberger reports in the New York Times, comes from the least powerful tornadoes, the ones that touch down briefly without causing much damage. Those are exactly the kind of tornadoes that would have been missed by meteorologists in the days before the Weather Channel and Doppler radar--scientists today would almost never miss an actual tornado touchdown, no matter how brief or weak. That makes it very difficult for researchers to even be sure that the actual number of tornadoes is on the rise, let alone, if they are, what might be causing it. The number of severe tornadoes per year has actually been dropping over time.

It is true, however, that as the climate warms, more moisture will evaporate into the atmosphere. Warmer temperatures and more moisture will give storm systems that much more energy to play with, like adding nitroglycerin to the atmosphere. This month's possibly record-breaking tornadoes are due in part to an unusually warm Gulf of Mexico, where as Freedman reports, water surface temperatures are 1 to 2.5 C above the norm. The Gulf feeds moisture northward to storm systems as they move across the country, and that warm moist air from the south meeting cool, dry air from the Plains often results in some powerful weather. But at the same time, other studies have forecast that warmer temperatures will reduce the wind shear necessary to turn a routine thunderstorm into a powerful system that can give birth to tornadoes. So in a hotter world we could see more frequent destructive thunderstorms, but fewer tornadoes--although some researchers think we could still end up with both.

What does it all mean? For one thing, we should remember that tornadoes--and other severe weather systems--have always been with us, and almost certainly will be, whatever happens to greenhouse gas emissions and temperatures in the years to come.

If you read the full story, there's also some great information about the role prediction and warning systems have played in lowering the death toll of tornadoes. Just as with earthquakes and tsunamis, using science and public systems to make sure people know what's coming is an important part of keeping people safe, no matter the circumstances.

P.S.: The video above was filmed by Christopher England, a University of Alabama employee. In an interview with a local CBS news affiliate he tells the heart-stopping story of how the video was shot. England, it seems, was with several coworkers in a storm shelter, but the power was out and nobody was sure what was going on. He went upstairs, to his third floor office to look out a window. This video is what he saw.


  1. I definitely agree that much of it’s perception. There’s so much focus on the weather these days, and such better equipment tracking it all.

    On a different note, I keep watching this video over and over and being astounded at nature. I’ve seen cloud rotation in person, but never a full-blown funnel, and absolutely nothing on par with this tornado. That had to be utterly terrifying.

  2. There’s been a notable increase in Category 5 hurricanes in the last two decades as well, which I doubt is related to more sensitive instruments.

  3. It’s a great video because of the soundtrack.

    The Japanese have raised the bar with their recent videotapes of the tsunami. If you are going to compete with them, you are going to need a good telephoto lens and a tripod.

    But the sound track can’t be beat. None of the usual incessant “aawmigaad”* squealings that usually ruin such shots. Just the deep breathing of someone who has just run up three floors and knows they ought to be running back. Deeply, deeply creepy.

    * A local word. Means “rather unusual for the time of year” I believe.

  4. We used to have wildfires in California and tornadoes primarily in Texas/Oklahoma/Kansas. Now the wildfires are in Texas and the tornadoes shifted east as well.
    This is what happens when large earthquakes shift the Earth’s axis.

  5. Having been in a tornado, I find this invigorating, terrifying and sublime in equal measures.

    2 years go I saw the sickly green-black creep of a sky descend on us and heard the roaring jet-engine winds turn silent for the eerie “calm before the storm”. I spent our tornado huddled in the basement, watching things fly by the window: the barbecue, outdoor furniture, chunks of our barn and parts of other people’s houses. I never got to see the actual funnel because I was safely below ground facing east and it passed on the west. Part of me wishes I’d stayed to watch for the funnel, but most of me is thankful I didn’t get killed by the flying wood, metal and glass that pounded the house and left such destruction in its wake.

    For the record, we live 45kms north of a designated “tornado alley”, but the storms have been creeping northward for the past 10 years.

    1. I grew up in Minneapolis. It was considered to be the northern extent of Tornado Alley (does that mean the north end is now somewhere around St. Cloud?). I moved to Michigan 15 years ago. The furthest from Tornado Alley I’ve ever lived. People here are pretty stupid about tornadoes. They all want to see one up close and personal. They simply can’t figure out why I head for shelter when the sky turns green after it hails. Been there, done that, don’t care to die by random 2×4 impalement.

  6. I will say that having lived in PA for the last 18 years now, I am aware of having more REALLY bad storms in the last eight than we had the previous 10. AND, we have had more tornadoes and tornado warnings in Pennsylvania in the last four years than in the previous 14.

    For example, between 1881 until 2003, Lebanon county had 13 tornadoes (, for an average of 1 ever 9 years. This month, they’ve had two already. Ditto the other counties surrounding the Harrisburg area. Obviously, none of them are as destructive or deadly as the ones in the South, and I don’t want to take the spotlight away from the tragedies there. Anecdotally, the number of storms is increasing.

    If you don’t want just anecdotes, go to NOAA’s website: and see, the year started off below average but has since exploded for the count of tornadoes nation-wide, with a preliminary count of 685 in April alone.

  7. I watched that video while listening to Pandora playing the first part of Russell Gunn’s “Shiva the Destroyer” (sorry, can’t find a link. Bizarrely appropriate with the deep breathing.

  8. Let’s not get carried away and blame global warming for this. Considering the damage is being compared to the last outbreak of so many tornadoes… in 1974… I’d say we should wait to see a drastic upward TREND before we start to seriously discuss it as a result of global warming. Right now it’s just a bunch of tornadoes, just like once a century you get a hundred-year storm which is the result of the right circumstances, not the result of global warming or anything else.

  9. @IronEdithKidd – I live right across the lake in western Ontario, just south of the town of Owen Sound. we’re due east of Huron National Forest in MI.

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