December is typically the least active month for tornadoes in the United States, but a powerful outbreak of more than 30 tornadoes hit six states in the mid-Mississippi River Valley Friday night, killing at least 88 people.
Scientists still have a lot to learn about the connection between climate change and tornado outbreaks because any links between them are “difficult to calculate,” NBC Miami Meteorologist Ryan Phillips told NBCLX. Tornadoes formed long before human-caused climate change, but climate change appears to be influencing the conditions which allow twisters to form.
“We cannot assume or rush to connect a warming climate to individual events. But the frequency, or infrequency, of these events should make us take note," Phillips said.
How does climate change affect tornadoes?
When, where and how often tornado outbreaks occur could be increasingly unpredictable as the planet warms. The less we’re able to anticipate tornado outbreaks, the more dangerous and deadly they could become. For example, Phillips said one of the reasons this past weekend's tornadoes were so deadly was that they occurred at night.
"Those who need to receive the warnings are likely asleep or disconnected from the weather situation. In some instances … those receiving the warning cannot see the threat for themselves and may not feel that their life or property is at risk."
Typically, tornadoes are not large in size and do not impact a large geographic area. But one of Friday's tornadoes, now being called the "Quad-State Tornado," hit four states — Arkansas, Missouri, Tennessee and Kentucky — in four hours.
To form, tornadoes require specific conditions like warm, humid air and wind shear, a phenomenon in which winds blow in one direction near the surface of the Earth and in different directions at higher altitudes. "The latest science indicates that the combination of these factors is increasing over time, particularly in the winter months in the south central and southeastern states," Michael Mann, climate scientist and author of "The New Climate War," told NBCLX.
"The latest science also indicates a trend toward more intense, destructive tornadoes. The tornado that hit Mayfield, Kentucky, was at the upper end of the scale, with radar-measured winds that neared 300 mph," he continued. "The impacts of climate change are no longer subtle. We’re seeing them play out in the form of these profound extreme weather disasters."
These conditions over the weekend “were not December-like at all,” Phillips added. "If this happened in March, April or September, we might not examine the event with this lens."
Research on climate change and tornadoes
Friday's tornado outbreak aligns with previous research that found peak tornado activity pushing into winter, beginning nearly a week earlier over the past few decades. Another study found that previously less active seasons for tornado outbreaks, like December, will become more active as the planet warms; over the last 40 years, it found that days favorable to tornadoes are decreasing in Texas and the Plains while increasing across the Southeast and Midwest.
Scientists at Columbia University also recently predicted that for every 1 degree celsius the planet warms, we could see favorable conditions for tornadoes increase by up to 20%. That doesn’t necessarily mean tornadoes will happen more often, just that they would be possible more often.
The American Meteorological Society warned that a warming planet could increase the overall risk of tornadoes in the United States by the end of the century. The findings suggest Americans could be up to 36 times more vulnerable to severe storms because of a combination of changes in when and where tornadoes happen along with where we live. Although it’s still a low-risk region, FEMA noted the potential disaster of a tornado hitting New York City.