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Tornadoes May Be Getting Stronger—or Not

The views expressed are those of the author and are not necessarily those of Scientific American.

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Sometimes scientists can’t help themselves from showing dramatic curves, even though they have so many caveats that no firm conclusions can be made from the data. James Elsner at Florida State University has a killer curve, and lots of caveats. The curve indicates that tornadoes in the U.S. may be getting stronger. The caveats indicate they may not be.

“If I were a betting man I’d say tornadoes are getting stronger,” he noted on Tuesday during a lecture at the annual American Geophysical Union fall meeting in San Francisco. But when asked directly at a press conference whether that is the case, he would not commit. “I’m not doing this [work] to establish the future intensity of tornadoes,” he explained, but to establish a method that someday could indeed determine if the storms are becoming more powerful.

Because the lecture was titled “Are tornadoes getting stronger?” the audience expected an answer. And their consternation rose when Elsner showed his final graph, adding up the kinetic energy of tornadoes each year from 1994 to 2012. The curve is flat from 1994 to about 2006 but then spikes upward through 2012. It was reminiscent of the now famous “hockey stick” graph produced by Michael Mann and colleagues a decade ago, indicating that Earth’s temperature had been flat for 1,000 years and began spiking upward in the mid-1800s. But Mann had 1,000 years of data; Elsner has 18. His data begin in 1994 because that’s when Doppler radar, the best at tracking tornadoes, began covering the entire U.S.

The point of the curve, however, is to show that measuring the length and width of a tornado’s damage path gives an accurate indication of its strength, which is driven by the storm’s peak wind speed. It is difficult if not impossible to measure that speed directly, as is done for hurricanes by ground instruments and planes that fly into the storms.

Despite the caveats, several interesting and solid conclusions do arise from Elsner’s painstaking work to map every single tornado that made landfall since 1994. Top winds speeds appear to be rising. And the stronger the storm, the longer it stays on the ground and the wider its path of destruction. Storms that ranked a 4 on the EF scale (1 to 5, with 5 the worst) cut paths with a mean length of 43 kilometers and a mean width of 809 meters. EF5 storms had a mean length of 67 kilometers and a mean width of 1,390 meters.

Also intriguing is that slightly more tornadoes are forming in the springtime, and in December, while the frequency in June and July is down a bit. Storm strength seems to be increasing most in the southern-most portions of the country.

Of course AGU attendees, and reporters, asked Elsner several times if climate change is or might be making tornadoes stronger. He would not bite. “I’m not claiming this is because of climate change,” Elsner told the audience. “But it is provocative, isn’t it?” He later noted that more moisture in the atmosphere, a general result of global warming, could provide more fuel for stronger tornadoes, but that no one has proven such a link. Changes in the El Nino – La Nina cycle of ocean and atmosphere conditions in the Pacific Ocean could be affecting the frequency of tornado formation, “but that research is just beginning,” he said.

Elsner was clear about not being able to say with certainty if tornadoes are getting stronger, and was careful to not speculate on a cause if they are. He also seemed to sense his audiences’ disappointment. The purpose of his work, he said, is to establish a scientifically rigorous method for determining tornado strength, which some day might answer the bigger questions. After years of skepticism, he noted, “the public has accepted that there is a link between hurricanes and climate change. We are just beginning” to determine whether there is any linkage for tornadoes.

Photo courtesy of Justin1569 at WikimediaCommons

Mark Fischetti About the Author: Mark Fischetti is a senior editor at Scientific American who covers energy, environment and sustainability issues. Follow on Twitter @markfischetti.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. ErnestPayne 1:29 pm 12/11/2013

    While increasing strength is interesting increasing frequency should be the big problem. Given the “quality of building” it doesn’t take much of a big bad tornado to blow your house down.

    Link to this
  2. 2. Shoshin 1:54 pm 12/11/2013

    Way to censor comments. You must also work at the LA Times.

    Link to this
  3. 3. Sisko 1:56 pm 12/11/2013

    Contrary to ongoing claims from alarmist media there are no mentions of tornadoes and hurricanes in the extreme weather events section of AR5. They give low confidence to tropical storm activity being connected to climate change, and don’t mention mesoscale events like tornadoes and thunderstorms at all. Similarly, they give low confidence to drought and flood attribution.

    That won’t stop alarmists however

    Link to this
  4. 4. jtdwyer 2:22 pm 12/11/2013

    “But it is provocative, isn’t it?”
    No – it’s insufficient data.

    Link to this
  5. 5. tuned 3:55 pm 12/11/2013

    Nice graph of real data.
    As always the Fossil Fuel portfolio lobbyists will ignore it, as they the do the whole towns and small cities (Tacloban, etc.) being swept away with horrifying regularity now.

    Link to this
  6. 6. hkraznodar 11:18 am 12/18/2013

    @Shoshin – Try not being a jerk. It does wonders for getting you posts allowed.

    @Sisko – Maybe we didn’t read the same report. They didn’t mention thunderstorms by the name “thunderstorm” but they did mention heavy precipitation events as more likely than not with medium confidence. They also listed drought as medium confidence. Then there was the high sea levels such as we saw with the recent hurricane along the Atlantic coast.

    You can nitpick and grasp at minor details but you also originally claimed that there wasn’t global warming. Then you said there is global warming but humans have nothing to do with it. Your track record on this issue isn’t too good.

    In areas where you have expertise your comments are impressive. In this particular area they aren’t.

    Link to this

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