In recent years, numerous climate scientists have argued that climate change plays an indirect role in tornadoes. They argue that their research indicates climate change may make the conditions that lead to tornadoes, like warm wet air at low altitudes, more frequent. However, the connection between climate change and tornadoes may be quite weak. Critics of the climate science consensus argue that the connection to tornadoes is weak at best. They also point out that the evidence actually suggests that the frequency of tornadoes is not increasing the way one might expect.
A tornado, according to University of Illinois meteorologists, is "a violently rotating column of air" which descends from low-lying clouds and makes contact with the ground. Tornadoes are a relatively common weather phenomenon, especially on the North American Great Plains, and they can cause severe damage to property and endanger lives when they touch down near human settlements. This is especially true of the minority of tornadoes, which are extremely strong.
When tornadoes, hurricanes and other extreme weather events happen today, it is increasingly common for weather reporters and others to speculate that climate change may be to blame. Recent Yale University research indicates that almost three in four Americans suspect there is a connection between climate change and extreme weather conditions, too.
However, climate scientists who believe that climate change plays a role in tornadoes argue that the connection is subtle and indirect. Kevin Trenberth, a researcher at the National Centre for Atmospheric Research, explains that tornadoes are "a weather phenomenon" caused by thunderstorms in which wind begins to undergo a particular type of rotation. With or without rapid climate change, the weather would give rise to many tornadoes each year.
However, says Trenberth, climate change is projected to increase the amount of warm, moist air in the lower atmosphere. Those are the conditions which are known to contribute to tornado formation. Grady Dixon, a geoscientist at Mississippi State University, says that "a warming environment leads to more storms and more intense storms." The effect might not be that strong. Trenberth believes that climate change probably has only "a 5 to 10 percent effect in terms of the instability and subsequent rainfall." However, that could still have a significant effect in terms of more tornadoes, as well as increasing the severity of tornadoes that might have formed anyway.
Science is still uncertain about a potential link between climate change and tornadoes, however. At the very least, scientists caution, it would be premature to conclude that every damaging tornado which occurs today, or even most of them, can be blamed on climate change. After a deadly tornado struck parts of Oklahoma in 2013, University of Colorado scientist Roger Pielke told the New York Times that so far the American statistics show "no long-term increase in tornadoes." In addition, over the past century, tornadoes have actually become a less serious threat to human life because of improvements in shelters, weather alerts and other emergency systems. The reason climate change may not contribute to tornadoes as much as might be expected, says another scientist, is that, while a warming climate means warmer, wetter air, it also appears to reduce the incidence of wind shear, which is another essential contributor to tornadoes.
As a result, while climate scientists continue to research the role climate change plays in tornadoes, the conclusions so far are tentative and controversial at best. Many scientists argue that tornadoes are likely to become somewhat more frequent as a result of rapid human-caused climate change, while others argue that the tornadoes which the United States and other countries experience today would have occurred anyway and so far have not grown any more frequent or deadly as a result of climate change.