Climate Change May Be Shifting The Path Of American Tornadoes

There are roughly 1,000 tornadoes per year in the US. solarseven/Shutterstock

Climate change is the problem that makes every other problem worse, from the global economy to the flooding of major cities and isolated islands. However, much of the focus of the impact of pumping so much carbon dioxide into the atmosphere is on natural disasters, particularly hurricanes and flooding, and study after study suggests that these will only become more potent over time as the world warms.

A new study reveals that another natural disaster – a common yet poorly understood one at that – may also be affected by man-made climate change. Tornadoes, as it turns out, are shifting their path of destruction across the US, and there’s a decent chance that this is down to mankind’s detrimental influences on the planet.

This research, which appears in the Journal of Applied Meteorology and Climatology, looked at the appearance and vectors of tornadoes across America over the last 60 years. They split them into two groups: those from 1954 to 1983 (a time of cooler temperatures) and those from 1983 to 2013 (a time of increasingly warmer temperatures).

Curiously, there has been a decrease in both total tornado days and number of individual tornadoes over time in “tornado alley,” a colloquial if not scientifically-defined region that encompasses (at least) northern Texas, Oklahoma, Kansas, and Nebraska. In fact, one large swath of Oklahoma went from having the greatest number of annual tornado days in the first period to experiencing the largest decrease in tornado days by the end of the second period.

However, there has been an increase in an area called “Dixie alley,” another tornado-prone region that includes Georgia, Alabama, Mississippi, Tennessee, and Louisiana. Specifically, central Tennessee had the greatest increase in tornado days between the first and second periods.

In effect, this means that the concentration of tornadoes has shifted from the central US to the southeast over time. Although it’s not clear why this has happened, the marked change in regional temperatures certainly match up with the shift.

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The rough region of Dixie alley, which contains particularly strong and violent tornadoes. Bhockey10/Wikimedia Commons; CC BY-SA 3.0

“The geographical shift in tornado activity has been established through powerful statistical methods and is shown to occur during two successive 30-year periods moving from a colder weather pattern to warmer conditions,” lead author Ernest Agee, a professor in the Department of Earth, Atmospheric, and Planetary Sciences at Perdue University, said in a statement. “More research is needed to search for changing climate trends responsible for tornado formation and this geographical shift, but climate change is a distinct possibility.”

Correlation isn’t always causation though, and more data is required to firmly pin down this link. As aforementioned, tornadoes aren’t fully understood phenomena, and unlike hurricanes, they aren’t directly powered by warm sea surfaces.

However, rising sea temperatures does mean that more evaporation occurs at the surface, which ultimately increases the atmospheric moisture content. Increased air moisture, along with rapidly rising air, is known to produce more thunderstorms, and this is why they occur more in the summer – and more frequently as the world warms due to climate change.

Tornadoes form when a thunderstorm begins to rotate and a denser, rain-filled center collapses to the ground. Therefore, if thunderstorms are more frequent during warmer seasons, it stands to reason than tornadoes will be too. As for the shift towards the southeastern US, this may be due to the proximity to the warming coastal waters, and thus the increasing amounts of rising, moist air – but again, more research is needed to confirm this.

Tornado alley, here pictured in red. Dan Craggs/Wikimedia Commons; CC BY-SA 3.0

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