On Dec. 14, 2021, Ben Adler, Yahoo News’ senior climate editor, wrote an article titled “Why climate change is likely to cause more devastating tornadoes.” He wrote about all the EF-4 scale twisters that began in northwest Tennessee three days earlier, moving across western Kentucky, resulting in multi-billion-dollar property destruction and causing at least 90 fatalities.
“I don’t think we’ve seen damage at this scale, ever,” Kentucky Gov. Andy Beshear said. Unfortunately, tornado damage on this scale will probably recur, because climate change will likely increase the frequency and severity of tornadoes, according to climate scientists. Adler wrote that while the causal link between climate change and tornadoes is less well established than it is for other extreme weather events, like hurricanes, it does create the conditions most conducive to tornadoes. But the strongest statement that can presently be made about tornadoes and climate change is that there’s really no clear historical signal. But there is increasing evidence from climate model simulations that tornado-producing environments may occur more in the future, particularly in winter.
There’s more uncertainty about the effect of climate change on tornadoes, because they are relatively uncommon globally, thus not well understood. “It’s really difficult to get data because we do not have good records of tornadoes going back very far,” said Daniel Swain, a UCLA climatologist. “Unlike thermometers or rain gauges, we don’t have lengthy records. Tornadoes are really sparse. Every weather station on Earth experiences some downpours and a heat wave or two every year. The average weather station on Earth is never hit by a tornado in its entire existence.”
Whether tornadoes are increasing in frequency the way that hurricanes and heat waves are remains unclear. Many more tornadoes were recorded in the last 20 years than in the previous 20, which may be due to more tracking. Swain said, “You can approach it sort of indirectly, by asking about atmospheric environments that are favorable to tornado development, or severe tornado development. Tornado scientists say ‘We know what these ingredients are that produce tornadoes, so we can look at those ingredients. How are those ingredients changing?’ Those environments that lead to tornadoes are exactly the kind of environments that become more prevalent because of global warming.
“All tornadoes come from thunderstorms,” Swain said, and thunderstorms become more severe on average with warmer weather and the resulting higher rates of evaporation. “With each degree of warming, or even every half degree of warming – it’s surprisingly striking, even relatively small amounts of warming.” Kentucky’s tornadoes thus are connected to the unusual heat wave that has engulfed much of the country. Severe tornadoes may become more common because of climate change in the southeastern U.S. in winter.
“The most robust increases in these tornado-producing environments seem most likely to happen in what used to be cooler times of the year,” Swain said. “In winter, historically, you didn’t have a lot of heat and humidity. So what seems to be happening, the most plausible connection to climate change, is that in these cooler season months, you have a lot of warming and additional moisture in the atmosphere.” He stressed that immediately before the Kentucky tornadoes struck, there were abundant record-high temperatures and record-high dew point levels in the atmosphere being set. The Gulf of Mexico was experiencing record warm temperatures for this time of year. That would be very consistent with the main mechanism people have proposed as to why climate change would influence tornadoes.
This reasoning is bolstered by recent research. A study published last month in the academic journal Earth’s Future modeled the effects of warming on the creation of “convective environments” leading to tornadoes. Researchers found that each degree Celsius of average warming increases the frequency of convective environments by 5% – 20%, especially in the Northern Hemisphere. Experts caution, however, that direct links between tornadoes and climate change remain unproven. Echoing Swain’s analysis, John T. Allen, professor of meteorology at Central Michigan University, wrote that climate projections for the late 21st century suggest that conditions favorable to the development of the severe storms that produce tornadoes will increase over North America, and the impact could be greatest in autumn and winter.
Meteorologist Harold Brook of NOAA told the BBC that while the increasingly common tornado clusters “clearly imply that the patterns of the atmosphere have changed … that may be related to climate change – we cannot make a full conclusion.”
James Elsner, a geography professor at Florida State University, compared climate change’s influence on tornadoes to the relationship between fog and car crashes. “You might see that, for example, when it’s foggy, there’s more crashes, but you don’t say the fog caused the crashes. If you think about climate change as the fog, we can’t really say it caused the accident, but it contributes.”
Conspicuous by its absence in the discussions of the above scientists is the impact of increasing greenhouse gas (GHG) emissions on global warming or climate change. While carbon dioxide (CO2) doesn’t entrap solar radiation as intensely as other GHGs, it is by far the most prevalent. All animals expire CO2; all petroleum-consuming engines “expire” CO2. All plants metabolize CO2 and expire oxygen (for animals to breathe). Plants that do a good job of metabolizing CO2 into their body tissues efficiently form soil organic matter, keeping carbon in the soil and out of the atmosphere. Unfortunately, the most common crops, in terms of total U.S. acreage, are the summer annuals corn and soybean, which, slowly but surely, deplete soil organic matter, thus deflecting CO2 skyward. Soil scientists say organic matter averages 58% carbon. Assuming that six inches of topsoil in each acre contains 1,000 tons, losing 1% of organic matter means that 11,600 pounds of carbon was liberated into the atmosphere. Climatologists are connecting the dots; hopefully agronomists and the people they advise will do the same.