Tornadoes killed 553 Americans in 2011, the deadliest year since 1925.  May 22 marks the 10th anniversary of the Joplin, Missouri tornado that killed 161, the first triple-digit toll since 1953.  The U.S. had been averaging 60 tornado deaths annually.

This death toll shocked the public, weather forecasters, and researchers.  Improvements in weather radar, National Weather Service warnings, and the advent of real-time, street-level tracking had seemingly rendered such death tolls a historical relic. 

Some experts had a ready answer for the devastation: man-made climate change.  Bill McKibben took a tongue-in-cheek tack in the Washington Post, with a headline, “A Link Between Climate Change and Joplin Tornadoes?  Never!”  He opined, “When you see pictures of rubble like this week’s from Joplin, Mo., you should not wonder: Is this somehow related to the tornado outbreak three weeks ago in Tuscaloosa, Ala., or the enormous outbreak a couple of weeks before that.”  Researchers Kevin Trenberth and Michael Mann also stated that global warming is making tornadoes worse.

When the unexpected happens, researchers need to ask why and examine the data.  Kevin Simmons and I had just published a book on the societal impacts of tornadoes.  We sought to assess whether the 2011 death tolls were due to the tornadoes which occurred, societal vulnerability, or perhaps some other factor.  We published our findings in a book, Deadly Season: Analysis of the 2011 Tornado Outbreaks, and a paper in Natural Hazards Review.

Our conclusion: it was the tornadoes.  The total number of tornadoes rated EF-5 on the Enhanced Fujita Scale for tornado damage, the highest rating, provides a short answer.  Six EF-5 tornadoes occurred in 2011, including four in Mississippi and Alabama on April 27.  The nation averages less than one per year (59 since 1950), with only one since 2011.  The year’s activity was extreme, but not unprecedented. For instance, seven EF-5’s occurred in the April 3, 1974 tornado outbreak.

Historical ratios of fatalities per injury, per millions of dollars of property damage, or per building damaged provide more detail and context.  For example, prior to 2011, violent tornadoes killed one person for every $20 million of property damage; this and similar ratios held steady in 2011.  The year’s many long-track, violent tornadoes produced enormous damage, with the corresponding casualties.

We further applied statistical models of tornado fatalities we used to examine the impacts of Doppler radar and NWS warnings.  The models controlled for tornado and path characteristics like EF-scale rating, path length, and the numbers of persons and mobile homes in the affected counties.  Plugging the characteristics of 2011 tornadoes into the model would give a fatality estimate, based on recent patterns.

The analysis predicted more than 500 fatalities for the year’s tornadoes with a high likelihood of a tornado killing more than 100.  Keep in mind, the deadliest tornado over the years used in the statistical analysis (1990-2010) killed 36 people.  The tornadoes of 2011 were unlike anything we had witnessed for decades.

There was no upward trend in violent tornadoes prior to 2011; the year was a clear statistical outlier or Black Swan type event.  Consequently, we concluded that fatalities should return to the prior normal or decline further due to continued warning process improvements.  By contrast, proponents of climate change told us that Joplin and Tuscaloosa were the new normal due to global warming.

The U.S. has averaged 43 tornado deaths over the past nine years, with 76 in the deadliest year (2020).  We have had only 11 deaths so far in 2021 (although please knock on some wood when reading this).

Mother Nature can be extreme, variable, and fickle.  Events and years unlike recent experience are inevitable.  When unexpected (or inconceivable) weather events occur, we should try to figure out what happened and why, instead of lazily attributing it to man-made global warming.

Daniel Sutter (dsutter@troy.edu) is the Charles G. Koch Professor of Economics and the Director of the Manuel H. Johnson Center for Political Economy at Troy University and host of Econversations on TrojanVision.

Image: Lane Pearman

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