Climate Change: Tornado myth update

Wikipedia: One of several tornadoes observed on May 3, 1999 in central Oklahoma

AUSTIN, June 10, 2014 — A popular global warming myth is that “extreme weather” tornadoes are increasing in numbers and intensity. The myth is fueled by news media hype. NOAA’s Storm Event Database disagrees.

The 2014 tornado season is on track to be the weakest on record, according to Dr. Harold Brooks, a long-time senior research analyst at the National Severe Storms Laboratory in Norman, Oklahoma. According to Brooks, this is the third exceptionally weak year in a row.

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NOAA records show, as of June 3rd, there have been 35 tornado fatalities in 2014. That compares to 55 in 2013, 70 in 2012 and a whopping 553 in 2011 by June 3rd in those years.

My best guess is that this is the slowest start since 1915, and maybe even 1900
-Dr. Harold Brooks, National Severe Storms Laboratory, 4/22/2014

This year is not just unusual, according to Brooks, it’s unprecedented. Through May 22, the fewest number of U.S. tornadoes on record have been recorded.

From Aug. 7, 2013, through April 13, 2014, the Norman, Oklahoma NWS office set a new record for its longest tornado-warning-free stretch, at 316 days. The previous record was 293 days, set in 1991.

Just the facts

Returning to “extreme weather”, tallies of all major F3/F4/F5 and only F4/F5 tornadoes since 1950 show that intense tornadoes have decreased, not increased as the news media would have us believe.

The last bastion of hope for global warming theorists who believe that “extreme weather” tornadoes are increasing, rides on the shoulders of the biggest, bad-boy tornado of them all, the frightening F5.

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In the movie “Twister”, storm chaser Helen Hunt is the only researcher who’d ever seen an F5. It killed her father when she was a child; sucked him right out of their storm cellar while he valiantly struggling to hold the doors closed. That childhood tragedy drove her to become a tormented tornado hunter who risked her life seeking a way to increase tornado warning times by just a few minutes.

An F5 is the most terrifying tornado of all.

The F5 tornado record

Author/NOAA storm event database: F5 tornado events tallied by year from 1950-2013
Author/NOAA storm event database: F5 tornado events tallied by year from 1950-2013

NOAA’s complete record of F5 tornado events from its storm event database is included in this graph. Though statistically weak, it shows since 1950 that F5 tornadoes have decreased by 70 percent!

Alert readers may note that the number of F5s in the graph seem higher than they should be. They are. That is because the storm event database captures county-based tornado events. If a single F5 crosses county or state boundaries, then each time is entered as a separate tornado event.

Global warming theorists will cry foul, especially given the 70% decrease, but event recording has the distinct advantage of capturing not only the numbers of F5 tornadoes, but their implied intensity as well, if they are long lived and travel over great distances.

A strait up tally is unlikely to show a different result. Besides, there is sometimes uncertainty as to whether eyewitnesses, radar and/or the damage path show one or more tornadoes. There may be less uncertainty in county-based event recording.

Some have suggested that 63 years isn’t long enough to establish a meaningful trend. They correctly suggest that a longer record with larger numbers of F5s would be more accurate. The pre-1950 work of Thomas Grazulis, documented in the July 1993 text “Significant Tornadoes 1680-1991: A Chronology and Analysis of Events” is cited as a source of additional data.

NOAA’s storm database is a living document. That means it’s constantly being updated with new information as it becomes available. For NOAA, history doesn’t have a statute of limitations.

The above graph, no doubt, will be updated as new historical data comes online.

Brooks calls pre-1953 records of tornadoes “sketchy”, including NOAA’s own records. According to Brooks, pre-1953 data is less reliable because that was before the SELS program, precursor to NOAA’s Storm Prediction Center, was started in 1952.

NOAA’s data remains the best available until older records from Grazulis or others become accepted as complete.

More about “extreme weather” tornadoes

There are other less direct ways to determine if severe tornadoes are increasing or not.

NOAA/National Severe Storms Laboratory
NOAA/National Severe Storms Laboratory

Fatalities caused by tornadoes are decreasing. That should not surprise anyone.

Weather forecasting, building construction and tornado warning systems are much improved. People have more time to seek shelter. You’d expect deaths to decrease whether tornadoes are becoming more intense or not. We are simply better prepared for them.

The impact of improved tornado warning systems is plainly seen in a change in the damage/fatality ratio after the SELS program started in 1952.

Environment Hazards, 12/5/2012: Levelized cost of tornado property damage by year from 1950-2011
Environment Hazards, 12/5/2012: Levelized cost of tornado property damage by year from 1950-2011

This graph shows that property damage caused by tornadoes before 1980 was much higher than after 1980. Costs are levelized using three different methods so that an apples-to-apples comparisons can be made between the years.

A notable exception is the super outbreak of 2011 with very high property damage. However, since then 2012, 2013 and now 2014 are exceptionally weak tornado years with low property damages reported.

The graph comes from a scientific paper titled, “Normalized tornado damage in the United States: 1950–2011” published by Kevin M. Simmons, et. al, in the journal Environmental Hazards, 12/5/2012.

Again, part of the decrease in property damage over time is explained by better warning systems and more tornado-resistant building construction. Forewarned is forearmed.


NOAA’s yearly report of strong to violent tornadoes, which includes all F3/F4/F5 tornadoes, shows that damaging tornadoes have decreased since 1953. Remove the weaker F3 tornadoes from the tally and the results are still the same.

The last glimmer of hope for global warming proponents claiming that “extreme weather” tornadoes are increasing in numbers and intensity rested with the biggest of the big tornadoes, F5. But F5s show a 70 percent decrease since 1950 and there weren’t even any F5s at all in the first three years.

Truth is, with only 138 tornado F5 events in the entire NOAA database, a trend line has low statistical value given the wide scatter in F5 yearly tallies.

Even combined with decreases in both fatalities and property damage over time, the numbers do not conclusively prove that “extreme weather” tornadoes are decreasing.

But what all that does prove is that “extreme weather” tornadoes are not increasing! The tornado myth, hyped by the media and pushed by global warming theorists, is just that – a myth. It’s a myth that refuses to die.

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  • Harold Brooks

    The NWS database won’t be updated with historical information except in extremely rare situations (a damage category that got misentered for a 1973 event is the only one I’m aware of). The data through a couple of months ago are final.

    There’s strong evidence that the pre-1975 tornadoes are overrated compared to the 1975-1999 tornadoes and that post-1999 are probably underrated compared to 1975-1999.

    • Steve Davidson

      Thanks for your input. I’d read in some database documentation that historical data could be changed (and how it affects downloads), so I thought it happens more often than it does.

      Obviously, weak tornado data is overrated, but I’d hoped that data on stronger F3/F4/F5 events might be more complete further back in time.

      • Harold Brooks

        F2-F5 are overrated pre-75, F3-F5 probably underrated 2000-2007(? on the ending date).

        • Steve Davidson

          Thanks again… that implies to me that the downward trend in the F5 graph above, based on data from the storm event database, is bogus on several fronts. The trend wasn’t scientifically viable anyway given its microscopic R-squared value. 😉

          I assume the underrating after 2000 is because of the switch from “F” to “EF” ratings.

  • Michael

    I’m not a climate scientist but I am a physics student and, as such, I interact with scientists from many different fields on a regular basis. I also have an interest in tornadoes so I talk to our climate people quite a bit. All of them maintain that tornadoes increasing in intensity as a result of climate change is unknowable at this time. So I don’t know where you are getting this argument that climate change should make tornadoes become more common from, but it certainly does not seem to be from scientists. I could not find a scientific journal entry that conclusively gives an opinion one way or the other.

    • Steve Davidson

      I am not a climate scientist, either. Like you are now, I was a physics major in college. Your climate people are right, it is statistically unknowable
      whether or not “extreme weather” tornadoes are increasing. (low
      R-squared value)

      That is the whole point of this article! The AGW
      claim that “extreme weather” tornadoes are increasing in number and
      intensity is a myth.

  • Steve Davidson

    As fate would have it, two days after this article was written Mother Nature put in her two cents worth here locally last night!

    Austin was under a tornado watch, and then a warning up until midnight. A tornado touched down just west of Austin near the community of Joppa. A family huddled in a bathtub while their home was ripped off its foundation and tossed 150 yards through the air. Miraculously, no one was hurt. Home owner Trent Ashton described it as being “twirled” around.

    The NWS is on-site this morning to determine the Fajita rating of the tornado.

    About 7,500 customers lost power locally during fearsome T-storms producing perhaps 100 strikes a minute at their peak and knocked down trees over a wide area.