This AGU session asked that question directly and I covered this previously. Now that the video of the entire session is available, I thought it worth revisiting. Of course, the answer is “no”, even when they try to make a hockey stick out of it. Watch the video, especially at just before the 20 minute mark, where in Q&A the presenter (James B. Elsner) remarks that he’s “not even sure if the slope is completely real“.
Contradicting that. Elsner also said “If I were a betting man I’d say tornadoes are getting stronger”
I was going to write up something on tornado climatology myself, but in doing research on the topic, I decided to let NOAA’s Nataional Climatic Data Center speak to the issue, since they do a good job of refuting this hockey stick nonsense even before it was conceived.
Today, nearly all of the United States is reasonably well populated, or at least covered by NOAA’s Doppler weather radars. Even if a tornado is not actually observed, modern damage assessments by National Weather Service personnel can discern if a tornado caused the damage, and if so, how strong the tornado may have been. This disparity between tornado records of the past and current records contributes a great deal of uncertainty regarding questions about the long-term behavior or patterns of tornado occurrence. Improved tornado observation practices have led to an increase in the number of reported weaker tornadoes, and in recent years EF-0 tornadoes have become more prevelant in the total number of reported tornadoes. In addition, even today many smaller tornadoes still may go undocumented in places with low populations or inconsistent communication facilities.
With increased National Doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency. To better understand the variability and trend in tornado frequency in the United States, the total number of EF-1 and stronger, as well as strong to violent tornadoes (EF-3 to EF-5 category on the Enhanced Fujita scale) can be analyzed. These tornadoes would have likely been reported even during the decades before Doppler radar use became widespread and practices resulted in increasing tornado reports. The bar charts below indicate there has been little trend in the frequency of the stronger tornadoes over the past 55 years.
Elsner has an 18 year data set, which is derived from measuring the length and width of a tornado’s damage path to give an 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, even TOTO (TOtable Tornado Observatory for which I built the corona electrometer instrument) has had only occasional luck in doing so. Putting TOTO directly in the path of an oncoming tornado required an astronomical amount of luck, and so the project was abandoned.
So, like Mann’s hockey stick, Elsner’s data is a proxy, not the actual measurement, and the hockey stick slope we see (that Elsner says isn’t even sure is real) at the end of his graph is created by data from one year: 2011.
It’s the old familiar sensitivity to endpoints graphing problem.
But note in the second graph from NCDC, the year 1974, when the April super outbreak occurred. There were many more F3+ tornadoes in 1974 than in 2011.
If Elsner had the same path data for an 18 year period from 1957-1975 and plotted it, he’d get an even bigger hockey stick shape at the end. Statistical artifacts from short period data shouldn’t be used to draw conclusions.
UPDATE: Paul Homewood has a detailed analysis here: http://notalotofpeopleknowthat.wordpress.com/2013/12/13/are-tornadoes-getting-stronger-2/
- For discussion – the tornado “hockey stick” (wattsupwiththat.com)