Are Tornadoes Getting Stronger? Too Soon to Tell, But…

April 29, 2014

Tornado numbers are not good indicators of the effects of climate change, and probably won’t be for some decades.
Simple physics suggests that more energy into the system creates an environment that is, well, more energetic – see Dr. Noah Diffenbaugh’s interview above.

Because our means of detecting and measuring the strength of extreme storms has changed markedly, and more than once, over recent decades, trends for both the number of storms, which we are much better at detecting with new radar technology, and the strength of the storms, which have been measured by very subjective standards, are not consistent over a long enough period to give a good measure.


Scientific American:

“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.

(above, James Elsner’s press conference at AGU on the topic)

Chris Mooney in Mother Jones:

Until pretty recently, scientists really felt that they couldn’t say much about that question. “The issue of global warming and severe thunderstorms [which often result in tornadoes] has been an outstanding challenge for the scientific community,” explains Noah Diffenbaugh, an Earth scientist at Stanford University who has focused on the question. For instance, a recent consensus report on extreme storms and climate change, published early last year in theBulletin of the American Meteorological Society, found that there was “little confidence” of any trend in tornado occurrence, and also concluded that there were no clear changes in the environments in which these storms form.

In recent months, though, this consensus—that we really don’t know what’s happening with global warming and tornadoes—has been challenged by some interesting new research. To understand why, it helps to first grasp some basics on how tornadoes form, a crucial first step toward determining whether global warming may change them.

Tornadoes emerge in some, but not all, severe thunderstorms, powerful explosions of atmospheric energy that also frequently feature lightning, hail, strong winds, and intense rainfall. Scientific research has determined that while a variety of environmental and atmospheric conditions support severe thunderstorm development, two in particular are crucial. The first is that there have to be high levels of so-called “convective available potential energy,” or CAPE, which denotes the instability of the atmosphere, and thus how friendly it is to thunderstorm updrafts. The second condition is that there must be strongwind shear, defined as the difference in speed or direction of winds as one ascends from the surface higher into the atmosphere.

Based on this knowledge, researchers have turned to global climate models in order to predict how global warming could change the relationship between CAPE and shear in the the future. And for a long time, the two factors were basically expected to offset each other. Or as National Oceanic and Atmospheric Administration (NOAA) tornado researcher Harold Brooks put it in a 2013 paper summarizing the consensus: “Climate model simulations suggest that CAPE will increase in the future and the wind shear will decrease.” So even though higher overall heat might lead to the potential for more explosive storms, the expected decrease in shear meant that potential might not get realized. In other words, it was basically looking like a wash.

That conclusion fell into question late last year, though, with a paper by Diffenbaugh and two colleagues in the Proceedings of the National Academy of Sciences. Using a suite of the most state-of-the-art climate models, the researchers found, once again, that wind shear decreases under global warming. However, they also found that that didn’t really matter, because the number of days with both high CAPE and high shear nonetheless increased. “We find that in fact, at the monthly or seasonal scale, that decrease [in shear] does occur over the US,” Diffenbaugh says, “but it’s concentrated in these days with very low CAPE.” That means that the net number of days with high CAPE and high shear was still projected to increase in the future.

That means more favorable environments for severe thunderstorms in general, but what about the subset of those storms that produce tornadoes? For tornado occurrence, Diffenbaugh explains, wind shear very close to the surface appears to be particularly important. In their new modeling study, Diffenbaugh and his colleagues looked at this parameter too, and they found an “increase in the fraction of severe thunderstorm environments that have high CAPE and high low-level shear,” as Diffenbaugh puts it. As the authors wrote, this result is suggestive “of a possible increase in the number of days supportive of tornadic storms.”

The paper by Diffenbaugh and his colleagues represents “the first significant evidence that we might expect to see a change in tornadoes,” says NOAA’s Brooks.

Meanwhile, Brooks thinks he might have found a trend in a different area: actual tornado statistics.

In general, the scientific consensus has been that our tornado data just isn’t good enough to support the idea of any clear, historic trend in tornadic activity. But in his latest research, Brooks thinks he has detected a “pretty strong signal that there’s been an increase in the variability of tornado occurrence on a national scale.” What does that mean? Basically, an increase in erratic behavior: periods with little or no activity, followed by intense bursts of activity.

There’s been “a decrease over the last 40 years in the number of days per year with at least one F1 tornado occurring somewhere in the US,” says Brooks. “At the same time, there has been an increase in the number of days with at least 30 F1 tornadoes.”

As noted above, recent tornado behavior has certainly seemed pretty up and down. According to Brooks, in recent years we’ve seen records for the most tornadoes ever in a 12-month period, as well as for the fewest in a 12-month period. And Brooks says we are also seeing increasing variability in terms of when the tornado season actually starts. (Note: The relationship between Diffenbaugh’s research, and Brooks’ new finding, isn’t clear at this point.)

In summary, then, it would be very premature to say that scientists know precisely what will happen to tornadoes as global warming progresses. However, they have come up with some interesting new results, which point to potentially alarming changes. More generally, the upshot of this research is that tornadoes must change as a result of climate change, because the environments in which they form are changing.


Elsner’s solution was to drop the human factor. Instead, he looked at wind speed and the size of the damage path (its length and width) to gauge whether tornado intensity has changed since 1994. (The United States has been almost completely covered by Doppler weather radar since 1994.) Using the damage path to gauge intensity avoids problems such as analyzing tornado strength via the Fujita and Enhanced Fujita scales, which are based on observations by weather service officials, he said.

Elsner analyzed damage paths and wind speeds using a statistical model. The result: a sharp upward spike starting in 2000. He also looked at earlier data, since the 1970s, which showed a much slower rise.

Puzzling out how climate change alters tornados is the big next step, Elsner said. One way this could happen is by adding moisture (via humidity) to fuel storms in Tornado Alley, the storm belt where tornadoes spin up in the United States. Warmer air holds more moisture. But Elsner said it was also important to track tornadoes in Canada, because there are hints that big ridges and troughs in the jet stream’s powerful winds could be triggering more tornadoes up north, and fewer in the United States.

Here, my recent video on emerging extreme events in a warmer climate.


27 Responses to “Are Tornadoes Getting Stronger? Too Soon to Tell, But…”

  1. omnologos Says:

    I like Eisner’s approach. He’s not looking for climate change, he is studying tornadoes. If he will see climate change, it will be as a consequence of studying tornadoes. His work is valuable independently from climate change. Etc etc.

    As for an audience disappointed about tornadoes not yet increasing as expected, it is really a shameful episode. Do people realize they are sitting there HOPING that other people will die and suffer???

    • dumboldguy Says:

      Omno got here first with his usual quick and poorly thought out response. I am like the man with the broom following the circus parade and cleaning up after the elephants. It’s a shitty job, but someone has to do it.

      Omno likes Elsner’s approach?
      “IF” Elsner sees climate change?
      ETC ETC WHAT??????

      We know that Omno often does not understand what he reads, or maybe he missed this.

      “Elsner analyzed damage paths and wind speeds using a statistical model. The result: a sharp upward spike starting in 2000. He also looked at earlier data, since the 1970s, which showed a much slower rise”.

      We know that Omno does not think on a high enough level to see patterns, causality, and even correlation very well, but those of us who do just MIGHT think that the “spike” regarding tornadoes since 2000 and the “spikes” in many other evidences of climate change in that same time period mean something.

      I must stop now—I have been overcome by Omno’s maudlin “shameful-die and suffer-HOPING” BS and must go cry in a corner for a while. And not to go chicken or egg on us, but don’t people suffer first, THEN die?

      • omnologos Says:

        Why do you keep writing such rubbish…try to comment what Eisner said.

        “I’m not doing this [work] to establish the future intensity of tornadoes,”

        That’s what I like about the guy. He is not a climatechanger trying to extricate a climate signal somewhere somehow..he is a tornado researcher. Even if tornadoes are not good indicators of climate change at least for now, his work about them will continue.

        There is a huge difference compared to those whose livelihood depends on finding a climate change signal.

        • dumboldguy Says:

          Why is EVERYONE who questions the babblings of the all-knowing, all-seeing Omnologos ALWAYS accused by him of writing rubbish? Why does he always find himself in the position of defending HIS rubbish against EVERYONE else who comments on Crock? Has he EVER gotten a “thumbs up” from anyone?

          I DID comment on what Elsner said, and only a small part of it. Your comment was not about the science but more of a thrown off “cocktail party” opinion.

          Elsner (and all the others quoted) are doing the usual scientist’s “waffling” thing and refusing to be pinned down, but only a fool like Omno would deny that that there are no “climate signals” being uncovered and that climate change is not affecting tornado characteristics, Elsner is being particularly coy, but he must be very excited because his “stuff” DOES seem to have uncovered some data that correlates highly with other signals. Yes, the science is “unsettled” as they like to say, but only the WIFI deniers like Omno would fail to see the significance of this article and try to deny its implications.

          I know Omno is seriously science-impaired and English is his second language, but he MUST be able to grasp this quote from the article.

          “In summary, then, it would be very premature to say that scientists know precisely what will happen to tornadoes as global warming progresses. However, they have come up with some interesting new results, which point to potentially alarming changes. More generally, the upshot of this research is that tornadoes must change as a result of climate change, because the environments in which they form are changing”.

          PS I have been communicating with a friend in Arkansas about yesterday’s tornadoes there. He was among the lucky and suffered only a near miss. He is a conservative/libertarian and a paid Tea Party organizer who has spent his life in OK and AR, and has minimal science background, but even he thinks “something is going on with the climate” as it relates to tornadoes and the other extreme weather they have suffered out there over the past decade. He helped friends liquidate herds of cattle in OK because of the drought—they were suffering, so they sold them off to “greener pastures” so they wouldn’t die. I suspect he would say of Omno—-“Die and suffer? Tornadoes? The man must live in his mother’s basement rather than in the real world”

          • omnologos Says:

            I understand this is all beyond you, but my point has zero to do with the findings of Eisner, and all to do with his approach.

            Obviously when the approach looks strong and solid, the findings look strong and solid too. But then what can you understand really???

          • dumboldguy Says:

            You’re wasting our time with your squirming and denialism, Obfooz. Your OPINION about “approaches” is irrelevant. Science is about using different “approaches” to problems, and it’s the FINDINGS that have meaning. Come back and talk to us when you understand that the science in the findings outlined here may be “unsettled”, but they nevertheless tell us much.

          • redskylite Says:

            Well Omno did get a few thumbs up for his contribution to the dark snow project, and we are all in suspense to know of the modest climate change project he will soon be involved in.

            As I understand it he strongly does not approve of scientists having a predetermined point of view or “herd instinct as J.Curry puts it”, however as one good climate Professor explained to his class, scientists are like cats and do not herd together, and if one of them can disprove for instance that CO2 does not heat up the biosphere then they would and become very famous in the process.

          • omnologos Says:

            anybody who thinks that’s the way science works, hasn’t been around scientists 😉 – most of all, has never been involved in the painful process of getting funding for a science project.

          • redskylite Says:

            Omno – my God you are so cynical and bitter – Prof David Archer of Chicago is a realist and in tune with the problem, please try watching between 20.30 mins and 22.15 mins of this great lecture called lecture 21 “the smoking gun”.

      • Elephants dispute your comparison with the omniscient one. They claim to have better memories and intellect. As for the xcrmnt……

    • paulhow Says:

      “As for an audience disappointed about tornadoes not yet increasing as expected, it is really a shameful episode. Do people realize they are sitting there HOPING that other people will die and suffer??”

      This is a shameful distortion of what the article actually said. The disappointment is clearly about not getting a more definitive answer to the question, “Are tornadoes getting stronger?”, not about hoping people will die and suffer.

      • omnologos Says:

        not so fast…Elsner sensed “his audiences’ disappointment” at “not being able to say with certainty if tornadoes are getting stronger”.

        IOW the audience wanted to hear that tornadoes are getting stronger. IOW they (unwittingly, one hopes) wanted to hear that people are suffering more than in the past.

        • Jon Torrance Says:

          English isn’t your first language, is it? Or is it that you’re too stupid to realize the natural interpretation of those words is that he thought the audience wanted a definite answer to the question he posed in the title of his presentation, i.e. “certainty”, not that they necessarily wanted the answer to be “yes”. I’ll break it down for you:

          Yes = certain

          No = certain

          Maybe = not certain

          I don’t know = not certain

          Not enough years of data to be sure yet = not certain

          • omnologos Says:

            the old “English is not your first language” ruse…

            in the meanwhile, Mooney is happily reporting about…”potentially alarming changes”.

            Elsner’s lecture wasn’t titled “Are tornadoes getting weaker” either. Nobody would care, if tornadoes were expected to be getting weaker.

      • dumboldguy Says:

        Nice try, Paul—–you are 100% correct, and anyone who has not been driven away from this thread by Omno and mfellion will agree with you. Unfortunately, Omno believes only what he wants to believe, and truth and logic have no impact on him at all.

        Anyone who would continue to argue “….the audience wanted to hear that tornadoes are getting stronger….they wanted to hear that people are suffering more than in the past” is deluded and beyond reach.

    • Well, it IS good that some scientists are studying the Effects of climate change, but it’s not much difference (is there any difference?) between studying weather pattern changes and studying climate change. I don’t really see the distinction you’re making.

      • omnologos Says:

        Hope the quote I included in my previous comment clarifies my point.

        It is the same as tasking somebody to paint a picture of a mountain, and tasking somebody else to paint a picture of the snow on the same mountain. The former will include the snow if any, the latter won’t necessarily include the snowless parts of the mountain.

        • dumboldguy Says:


          No, Omno, none of your follow-on comments ever “clarify” anything, least of all your pointless points. That’s why you were recently called an obfuscator by someone else and I made fun of you with “Obfooz”.

          Lord love a duck, but your skull is thicker than depleted uranium.

          PS I just love “a painting of the snow on a mountain won’t (necessarily) include the mountain”. YOU’RE RIGHT! I just reached over and took a piece of blank paper out of my printer and lo and behold—-it’s a beautiful rendition of “Snow on Mount Omnos”. I have tacked it up above my monitor to remind me of your “blankness”.

          PPS We have a great article here to discuss, and somehow Omno has yet again made it all about him. Too bad.

  2. omnologos Says:

    Dumbo- you ARE the only one talking about me. Just stop. I thought that you were dishonest, then that you were dumb, but this waterfall of words against anything I write in all possible threads makes you look positively sick in your head.

    • dumboldguy Says:

      I am not the ONLY one “talking about you”, Obfooz. I’m the only one who is bothering to make visible comments—-note that you are gathering your usual number of “thumbs down” from those who want to tell you that you’re a fool but can’t be bothered to do more than click a “thumb”.

      I am neither dumb or dishonest—-YOU are, and that is proven by your ongoing denialism and attempts to project those attributes of yours onto me.

      I am a student of psychology and human behavior among many other areas of interest, and you are a very interesting subject for study. I would suspect that is why so many others on Crock pay you more attention than you deserve and seem to be obsessed with you even though we all know that we shouldn’t feed trolls. It’s perhaps not nice of us to take advantage of your handicap, but you’re our own little freak show on Crock, and we are only human. I think I speak for many when I ask in a half-amused, half-serious way—–“WHAAAAT???”

      You want the “waterfall of words” to stop? YOU can make that happen easily enough. Stop saying stupid things, and I for one will leave you alone.

      “….you look positively sick in your head”. Lord love a duck, but that is exactly the kind of mindless retort you should NOT be making if you ever want to establish any credibility or gain any respect here.

  3. mfellion Says:

    I wonder if all you folks are trolls. you never seem to talk about the actual subjects but delight in putting each other down. I have a suggestion, take that one way trip to mars and leave the rest of us in peace.

    • dumboldguy Says:

      Another demented rooster struts into the barnyard to peck at imaginary bugs, and is unable to see that his comment is of NO value here whatsoever—NONE, NADA. Perhaps he is bitter that we recognize that HE too is a denier troll and have pointed that out to him all too often?

      The strength of Crock is that “we folks” DO manage to share information and opinions about “actual” climate change subjects rather nicely 99% of the time, and save our “putting down” for the very few like you and Omno who deserve it. Take your stupid suggestion (no one is going to Mars anytime soon) and go away yourself. I have suggested you go hang out on the right-wing-whacko sites where you will meet other demented roosters to strut with. Please do so and leave US in peace.

  4. mfellion Says:

    I would leave you folks arguing this subject with a little data which should make the predictions of the guy in the article at least somewhat suspect. In 1000 AD it was hotter world wide than today, in 1625 AD it was a lot colder than today. We will reach the temperature of 1000 AD , assuming the models are correct, in 2100 AD. All that is from the various temperature reconstructions, look them up yourself try google 2000 year temperature reconstructions. If it was hotter in 1000 AD than per his “research” we should have had a lot of tornados and been blown away but our ancestors were still there long enough to make us. Perhaps the real problem is back in 1000 AD we had a lot less people standing around in a tornado. today we have people, houses, cars etc covering almost every square mile of land with something manmade, any weather will effect those items so viola tornados are worse . As a side note there is a government funded study you can google which claims tornadoes are no worse than in the past so maybe this study is just a bunch of crock.

    • dumboldguy Says:

      Ho-hum. More denier cherry-picking and misinterpretation.

      I’d be more inclined to listen if you would correct that little misspeak you made when you said “The earth’s climate has been changing for 4.5 billion years”.

      Do you recall that I said you were flat-out WRONG and said that you probably didn’t even know enough science to understand why?

      Not to “put you down” or anything—-just sayin’—-a man should know his limitations.

    • ubrew12 Says:

      “If it was hotter in 1000 AD than per his “research” we should have had a lot of tornados and been blown away” Who is ‘we’? In 1000 AD ‘we’ was in Europe and Asia. The people who owned this particular bit of property have been largely supplanted. Perhaps they WERE blown away.

      But its been demonstrated repeatedly that it WASN’T hotter worldwide in 1000 AD than it is today. Here, for example, is the last 2000 years (blue is ocean sediment data. green is GLOBALLY integrated tree-ring data. red is modern thermometer and satellite data.):
      Perhaps you saw a graph of historical tree ring proxy temperatures from early in the effort to understand their usage? Something from the 1970s or 1980s, say? If so, then the reason they show a hump of temperature around 1000 AD, is because in those early years of tree ring proxy calculation, all the tree rings they were using were in England. And, in fact, its well established that in 1000 AD, the N Atlantic experienced just such a warming, probably due to the Gulf Stream diverting its effects. But England is not the Planet. Indeed, in 1000 AD, Siberia was colder than usual.

  5. Dr. Elsner’s AGU presentation was an excellent lesson in statistics applied to tornadoes. Hopefully, the outcome of this month’s meeting with climate scientists and tornado scientists will be informative.

  6. […] de laatste tijd in de greep had: tornado’s. Verschillende blogs schreven over het onderwerp: Climate Denial Crock of the Week, het Weather Underground blog van Jeff Masters en de Rabett rende zelfs twee […]

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