Climate Change Will Increase the Number and Severity of Tornadoes

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Pro: Tornadoes are Getting More Dangerous

While there have been no long-term trends in the frequency of tornadoes, there have been changes in tornado patterns in recent years. Research has shown that there are fewer days with at least one tornado but more days with over thirty, even as the total number of tornadoes per year has remained relatively stable. In other words, tornado events are becoming more clustered.

There is also evidence to suggest that tornado patterns have shifted geographically. The number of tornadoes in the states that make up Tornado Alley are falling, while tornado events have been on the rise in the states of Mississippi, Alabama, Arkansas, Missouri, Illinois, Indiana, Tennessee, and Kentucky. 

There is speculation that some of these changes are linked to climate change and its effect on the jet stream. Tornado outbreaks have also coincided with rising ocean temperatures. But no one can say for certain that climate change is a contributing factor in these events. It is very hard to tease out which changes are due to climate change and which changes might be caused by interaction with natural climate fluctuations such as El Niño.

Is Climate Change to Blame

The fourth National Climate Assessment, [published by the U.S. Global Change Research Program (USGCRP)], summarizes the complicated relationship between tornadoes and climate change: “Some types of extreme weather (e.g. Rainfall and extreme heat) can be directly attributed [to] global warming. Other types of extreme weather, such as Tornadoes, are also exhibiting changes which may be linked to climate change, but scientific understanding isn’t detailed enough to project direction and magnitude of future change.” In other words, we still have a lot to learn about how climate change might affect tornadoes.

One thing we know for certain is that we live in a warmer, wetter world thanks to climate change, and this is likely to have an effect on extreme weather events, including tornadoes. Unfortunately, in the case of one of nature’s most violent storms, we cannot yet predict what that effect might be.

https://www.nationalgeographic.org/article/tornadoes-and-climate-change/

Con: Tornadoes are Getting Less Dangerous.

Finally, it would require several hundred years of detailed tornado data both before and after 1850 to accurately determine whether the natural trends and fluctuations of tornado activity have been altered by the 1.3 parts per ten thousand increase in atmospheric carbon dioxide since 1850.  This is the period during which human activity contributed a portion of the increase of CO2 in the atmosphere, most of which occurred since 1940. Without such sufficient data, no scientific comparisons and conclusions concerning the impact of the tiny increase in carbon dioxide in the atmosphere would be statistically meaningful.

Despite this lack of sufficient long-term tornado data, there is a very short period of historical data from 1950 to the present that can be analyzed.  This historical tornado data, show that the number of all categories of tornadoes has been declining for the past 45 years and the number of strong tornadoes, F3 or higher, has been dramatically declining for the past 45 years. 

In 2017-2018, the U.S. set a record for the longest period in tornado history without a tornado death, despite the dramatic increase in US population since 1950.

In 2017-2018, the U.S. set a record for the longest period in tornado history without an F3 or stronger tornado.

Tornadoes typically form when very cold, dry air clashes with very warm, humid air. Global warming theory predicts that the Arctic will warm more than the tropics and subtropics.  This would result in less, not more, of a clash between cold Arctic air masses and warm Gulf of Mexico air masses.  As a result, according to global warming theory, fewer and less violent tornadoes should occur.

Tornadoes typically form when very cold, dry air clashes with very warm, humid air. Global warming theory predicts that the Arctic will warm more than the tropics and subtropics.  This would result in less, not more, of a clash between cold Arctic air masses and warm Gulf of Mexico air masses.  As a result, according to global warming theory, fewer and less violent tornadoes should occur.

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.

https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends
Figure 1: Tornado frequency has been declining since the early 1970s. Data Source: National Oceanic and Atmospheric Administration, U.S. Tornado Climatology, Historical Records and Trends, https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends.

Figure 2, below, shows the decline in strong, F3 or higher tornadoes in recent decades.  

Figure 2: The frequency of strong tornadoes, registering F3 or stronger, has been declining since the early 1970s. Source: National Oceanic and Atmospheric Administration, U.S. Tornado Climatology, Historical Records and Trends, https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends.


References:

NOAA National Centers for Environmental Information/National Climatic Data Center page on U.S. Tornado Climatology

https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology

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