Rebecca Falconer

Climate change’s impact on U.S. cities

Climate change is affecting the United States in various ways, and one of the most significant impacts is being felt by its cities. As severe thunderstorms and tornadoes continue to tear through the South, Midwest, and Mid-Atlantic regions, experts are investigating the link between these extreme weather events and climate change.

In the past two weeks, more than 50 people have lost their lives due to severe thunderstorms and tornadoes, and another potentially significant outbreak is projected for Tuesday. At least 32 deaths have been confirmed from the latest storm system, which brought over 50 preliminary tornado reports, including in Alabama, Delaware, Illinois, Indiana, Iowa, Mississippi, Tennessee, New Jersey, and Arkansas. President Biden expedited a major disaster declaration to provide federal assistance to the Natural State.

Meanwhile, the National Weather Service’s Storm Prediction Center warns of an “enhanced risk” that severe thunderstorms will develop on Tuesday from Illinois southward to Arkansas. These could pose a risk for a few strong tornadoes, large hail, and damaging wind gusts.

Tornado Alley Moving

Tornadoes and tornado outbreaks are an area of active investigation for climate scientists. Victor Gensini, a meteorology professor at Northern Illinois University, told Axios in a phone interview Sunday that while the role of human-caused climate change in altering tornado characteristics is still in its infancy, records dating back over 70 years indicate a shift eastward from the traditional areas of the Midwest known as “tornado alley.”

“Texas, Oklahoma, Kansas, Nebraska, those kinds of areas are typically staying stagnant or decreasing in terms of the number of strong tornadoes they get every year,” Gensini said. “But then you see an increase in places like Tennessee, Mississippi, Alabama, Illinois, Indiana, areas that are the traditional area of the Great Plains,” he said. “And that’s incredibly important for the United States — as you go from the Great Plains, the population density rapidly increases.”

Harold Brooks, a senior research scientist at the National Severe Storms Laboratory in Norman, who wrote a study on tornadoes with Gensini, cautioned in a phone interview with Axios Sunday night that tornadoes are small-scale phenomena, occurring within thunderstorms that are themselves small in scale. This makes it difficult for researchers to decipher how climate change factors in with precision, Brooks noted.

Warming Alters Severe Thunderstorm Ingredients

Jeff Trapp, head of atmospheric sciences at the University of Illinois, said data suggests climate change is already altering one key ingredient in severe thunderstorm formation, a quantity known as “CAPE” (convective available potential energy). This metric helps to indicate how much atmospheric energy there is for thunderstorms to tap into, once they are triggered by a cold front or other mechanism. Higher CAPE indices are now more likely to be “found outside of the traditional tornado season of late spring/early summer,” Trapp said via email.

Studies show that while some severe thunderstorm ingredients, such as humidity and atmospheric instability, are likely to increase with a warming climate, others may do the opposite. Climate change is anticipated to decrease the amount of wind shear available to severe thunderstorms, which could deprive them of a key ingredient for tornado formation.

Tornado Season Shift

Trapp said that overall, the frequency of tornado activity in the U.S. has been declining, but the peak occurrence has shifted to earlier in the spring. “This shift is due in part to late winter/early spring tornadoes such as what we’ve seen this year,” Trapp added. “An increase in these ‘out-of-season’ events is consistent with climate model projections.”

Impact on Cities

The effects of climate change, including severe weather events like tornadoes, can have a significant impact on cities. In addition to the loss of life and property damage caused by these events, cities may also experience disruptions to infrastructure and essential services, such as power and transportation. Climate change can also exacerbate existing social and economic inequalities, as vulnerable populations are often the most affected by extreme weather events. Cities can take steps to mitigate the impacts of climate change, such as investing in infrastructure and emergency preparedness, promoting green energy and transportation, and developing plans for adaptation and resilience.