A warming world means deadly twisters, and the type of storms they spawn

The devastating tornado that decimated communities in Arkansas and Illinois on the night Dec. 10-11, 2021 was so unusual in its strength and duration, especially for December, that many people, including the U.S. president, were not prepared. asking what role climate change might have played – and whether tornadoes will become more common in a warming world.

These questions are much more straightforward than the answers, but research is uncovering new clues.

I’m an atmospheric scientistWho studies severe convective thunderstorms like tornadoes, and the effects of climate change. Here’s what scientific research shows so far.

Climate models can’t see tornadoes yet – but they can recognize tornado conditions

To understand how rising global temperatures will affect the climate in the future, scientists use complex computer models that characterize the whole Earth system, from the Sun’s energy streaming in to how the soil responds and everything in between, year to year and season to season. These models solve millions on a global scale of equations. Each calculation adds up and requires more computing power than a computer on a desk.

To project how Earth’s climate will change through the end of the century, we currently have to use a broad scale. This is similar to the zoom function of a camera zooming in on distant mountains. It is possible to see the forest but not the individual trees. Even if you blow up the image, a pine cone inside one of those trees will be difficult to see. Climate models show that the smaller an object is, the more difficult it is to see.

The scale of severe storms and tornadoes that they create is far smaller than what climate models can predict.

Instead, we can examine the large-scale conditions that make it possible for tornadoes.

Two key ingredients to severe storms include (1) energy driven warm, moist atmosphere that promotes strong updrafts and 2) changing wind speed and direction. wind shearThis allows storms to grow stronger and last for longer periods of time. The third ingredient is more difficult to identify. It is a trigger that causes storms to form. This could be a hot day or a cold front. Although severe storms and tornadoes are not always possible in every environment, severe storms are more likely when the first two conditions are met.

Climate models can help us understand the changing risk by using these ingredients to determine the likelihood that severe storms or tornadoes will form.

How storm conditions could change

Climate model projections of the United States suggest that the overall climate model projections likelihood of favorable ingredients for severe storms will increase by the end of the 21st century. The main reason for this is that rising temperatures and increasing moisture in the atmosphere increase the potential for strong updrafts.

Seasons that are usually considered to be rarely producing severe weather are experiencing significant changes due to rising global temperatures. Warmer, humider air is experiencing stronger increases in fall, winter and early spring mean there will be more days with favorable severe thunderstorm environments – and when these storms occur, they have the potential for greater intensity.

What do studies reveal about frequency and intensity?

We can simulate thunderstorms in these future climates over smaller areas. This helps us to predict whether severe storms will occur. Several studiesHave modeled changesTo the frequency of intense stormsThis will help you to understand the changes in the environment.

Already, we are seeing signs that the climate is shifting toward more favorable conditions for severe storms during the cooler seasons. However, the summertime probability of storms forming in the summer is declining.

Things get more complicated for tornadoes. Even with a forecast for the next day that is accurate, there is no guarantee that a tornado would form. Only a very small proportion of storms that occur in favorable weather conditions will produce tornadoes.

Numerous simulations have shown what would happen if a tornado outbreakDifferent levels of global warming can produce tornado-producing storms or other types of weather. Projections suggest that stronger, tornado-producing stormsGlobal temperatures rising may make it more likely, but the potential for stronger weather is less than we might expect due to an increase in energy availability.

The effect of 1 degree of warming

We know a lot about how warming climates influence severe storms and tornadoes, but most of it is localized in the United States. Not all regions will experience changes in severe storm environments at the same pace.

In a recent studyMy colleagues and I discovered that severe storms are more common in the Northern Hemisphere and that they increase at higher latitudes. Our research in the United States suggests that for every 1 degree Celsius (1.8 F), the temperature rises, there is a 14-25% increase of favorable environments in spring, autumn, and winter. The greatest increase in winter is most likely. This is due to the increase in energy available because of higher temperatures. This is not about tornadoes, but favorable environments.

What does this say about December’s tornadoes?

To find out if climate change affected the severity or likelihood of tornadoes in the December 2021 outbreakIt is difficult to attribute any one event like this to climate change. These are short-term influences. El Niño-Southern OscillationThis could also make the picture more complicated.

There are certain signs that point to a stormier future. However, it is still unclear how this will manifest for tornadoes.