The following essay is available for re-publication in The Conversation.
A lot of people, including the U.S. president, are wondering what role climate change might have played in the deadly tornado outbreak that tore through communities from Arkansas to Illinois in December of 2011.
Both questions are easy to ask, but research is giving new clues.
I am an atmospheric scientist who studies storms like tornadoes and climate change. Scientific research shows what it is.
Climate models can recognize tornado conditions.
Scientists use computer models to understand how rising global temperatures will affect the climate in the future, from the Sun's energy streaming in to how the soil responds and everything in between, year to year and season to season. The models solve millions of equations. Each calculation requires more computing power than a desktop computer can handle.
We have to use a broad scale to project how Earth's climate will change over the next century. Think of it as a zoom function on a camera. You can see the forest, but individual trees are hard to see, and a pine cone in one of those trees is too small to see even when you blow up the image. The object is harder to see with climate models.
Climate models can't predict the scale of tornadoes and storms.
We can look at the large-scale ingredients that make the conditions ripe for tornadoes to form.
Two key ingredients for severe storms are warm, moist air and changing wind speed and direction, which allow storms to become stronger and last longer. A third ingredient, which is harder to identify, is atrigger to get storms to form, such as a really hot day or a cold front. Severe storms are more likely when the first two conditions are favorable, but not without this ingredient.
Climate models can tell us something about the changing risk by using these ingredients.
The storm conditions are likely to change.
Climate model projections show that the likelihood of favorable ingredients for severe storms will increase by the end of the 21st century. Warming temperatures and increasing humidity in the atmosphere increase the potential for strong updrafts.
Changes for seasons that we think of as rarely producing severe weather are being driven by rising global temperatures. There will be more days with favorable severe thunderstorm environments because of the stronger increases in warm air humid in fall, winter and early spring.
What studies show intensity and Frequency.
We can model storms in the future in order to better understand how storms form.
We are already seeing evidence that the cooler seasons are more favorable for severe storms, while the summertime likelihood of storms is decreasing.
Things get harder for tornadoes. There is no guarantee that a tornado will form in the forecast. Only a small portion of the storms produced in a favorable environment will produce a tornado.
Simulations have explored what would happen if a tornado outbreak occurred at different levels of global warming. Projections show that storms may be more likely as global temperatures rise, though they may be less strong than we might think.
The effect of a degree of warming.
The United States is where we know the most about how a warming climate affects storms. Not all regions will see the same changes to storm environments.
In a recent study, colleagues and I found that the rate of increase in severe storm environments will be greater in the Northern Hemisphere. In the United States, our research shows that if the temperatures rise by 1 degree Celsius, favorable environments will likely increase in spring, fall and winter. Increased energy available due to higher temperatures is the main reason for this. This is not about tornadoes, it is about favorable environments.
What do you think about December's tornadoes?
It's difficult to say if climate change influenced the likelihood or intensity of the December 2021 outbreak of tornadoes. Shorter-term influences like the El Nio-Southern Oscillation may be complicating the picture.
There are signals pointing in the direction of a stormier future, but how this affects tornadoes is an open area of research.
The Conversation published this article. The original article can be found here.
