A tornado outbreak occurs when six or more tornadoes appear in close succession, usually over a period of up to three days. They tend to be behind the most fatal tornadoes, and they’re something that people in “tornado country” have good reason to be concerned about. And according to a recent University of Chicago study, they’ve doubled in frequency over the last half century.
First, a basic primer in how tornadoes form: Warm, moist air near the surface of the earth meets with cold, dry air at higher altitudes. This forms bands of thunderstorms. Some thunderstorms transform into supercells if the wind increases in strength and changes direction with height. In about 30 percent of cases, according to research meteorologist Harold Brooks, these supercells lead to the formation of tornadoes. This happens when air descending from the supercell causes rotating winds near the ground.
Earlier research had predicted that a warming climate would increase the “convective available potential energy” (CAPE) and storm relative helicity, a measure of vertical wind shear in certain supercells. This would cause an increase in severe thunderstorms, which would lead to an increase in the number of tornado outbreaks.
However, what the researchers found was that the increase in tornado outbreaks seems to be due to an increase in storm relative helicity, which does not seem to be connected to global climate change.
“Our study raises new questions about what climate change will do to severe thunderstorms and what is responsible for recent trends,” says study co-author Michael K. Tippett of Columbia University. “The fact that we didn’t see the presently understood meteorological signature of global warming in changing outbreak statistics for tornadoes leaves two possibilities: Either the recent increases are not due to a warming climate, or a warming climate has implications for tornado activity that we don’t understand.”
Either way, the end result is the same: tornado outbreaks have doubled in frequency, causing more fatalities and more property damage than ever before, and that is something we need to address. Knowing, for sure, that tornadoes are more frequent means we can take steps to protect people, animals, and property from them.
Knowing that tornadoes are increasing in frequency, increased funding for warning systems, monitoring, and shelters would obviously be helpful in minimizing damage and loss of life. Although people who live where tornadoes are common are well educated on what to do in the event of a tornado, considering that tornadoes are now being seen with more frequency in areas such as the American Northeast, better education on tornadoes, how and when they form, and what to do when one touches down, would be beneficial for all people.