Why tornadoes are the hardest disasters to link to climate change

After tornadoes hit six U.S. states late last week, killing at least 88 people and razing warehouses, nursing homes and factories, many were quick to blame global warming for at least part damage.

Over the weekend, numerous media speculated that global warming may have played a role and lobbied policymakers for answers. Deanne Criswell, the administrator of the Federal Emergency Management Agency, or FEMA, called devastating tornadoes “our new normal.” President Joe Biden, responding to a question from reporters at a press conference on Saturday, said “everything is more intense when the climate warms – everything” but stressed on Monday that “we cannot say with certainty absolute “that climate change was to blame.

The questions are hardly surprising: after all, it has become increasingly common – and scientifically substantiated – to attribute flooding, heat waves, and even intense hurricanes to the rise in temperatures due to the use of fossil fuels. Friday record heat has led many to speculate that climate change may have played a role in the disaster; there is also evidence that tornadoes are moving east, possibly due to temperature changes.

But tornadoes, scientists say, are extremely difficult to link to climate change. According to a 2016 report from the National Academies of Sciences, tornadoes are the most difficult weather event to attribute to global warming – after heat waves, forest fires, extratropical cyclones and even heavy snowfall. “They are the one extreme we have the least confidence in,” said Zeke Hausfather, climatologist and director of climate and energy at the Breakthrough Institute.

This is for several different reasons. First, most studies linking climate change to weather events (an area known as “extreme event attribution”) model global climate in two different ways: with global warming caused by man and without. But these climate models don’t have a resolution fine enough to simulate tornadoes, making it difficult for scientists to see how tornadoes might change in the years to come.

“Our models do not produce tornadoes,” Hausfather said. Climate models, he explained, divide the world into boxes 100 or 25 kilometers wide and simulate what happens in each box. But tornadoes do form in areas less than a mile wide – far too small to be easily modeled.

This means that scientists must use other methods to analyze how tornadoes will be affected by global warming. Tornadoes require a few different ingredients to form: First, the potential energy created by hot, humid air near the ground and cool, dry air above. In the so-called “Tornado Alley” in the central United States, for example, tornadoes are formed by warm air coming from the Gulf of Mexico to the southeast and cool air coming from the Rocky Mountains. Second, they require “wind shear,” a change in the speed or direction of the wind from the ground to the sky, to wind the tornado’s rotation.

Harold Brooks, senior researcher at the National Severe Storms Laboratory, says there is evidence that global warming could affect one of these ingredients, but not the other. According to Brooks, there is good evidence that the potential energy of storms could increase as the world warms. But the wind shear might decrease Where increase in a warming planet, and scientists do not yet know what effect will prevail.

To complicate matters, tornadoes can also be affected by the precise way thunderstorms form – whether they form as isolated storms, such as during catastrophic events on Friday, or as a huge line. Isolated storms are more likely to create tornadoes, according to Brooks. But, he adds, it is not yet understood how global warming could influence the exact mechanisms of thunderstorm formation.

Researchers argue that there may come a time when research clearly shows a link between tornadoes and a warming world. “Lack of evidence is not proof of absence,” Hausfather said. But at the moment, there is no clear data to indicate that tornadoes are increasing in number or intensity. (There are more tornadoes today than in the 1950s, but scientists say it’s because of changing monitoring techniques.)

And there are risks in going too far ahead of science. In an article published last week in the journal WIREs Climate Change, Swedish and American researchers argued that linking climate change to extreme weather events can mask how poor planning and failing infrastructure transform weather events. in disasters. “Even when science can attribute such events to human greenhouse gas emissions with some rigor,” the authors wrote, “the resulting damage is primarily a function of vulnerabilities on the ground”.

Stephen Strader, professor of geography at Villanova University, similarly argues that focusing too much on the role of global warming can get policymakers out of the woods. “It creates an air of ‘what can we do our hands are tied”, “he said. “Climate change is only one side of the coin of the disaster.”

In this case, Strader explained, the tornadoes were particularly dangerous for several reasons: many of them struck at night, when people were more likely to be sleeping or unwilling to evacuate, and they hit the southeast. from the United States, where there are many mobile homes and homes without basements or tornado shelters. (Last year, the Southeast recorded 83% of tornado-related deaths.) Many deaths, meanwhile, occurred in a few buildings – an Amazon warehouse and a candle factory – that were razed to the ground.

Strader said he hopes the recent wave of tornadoes will boost preparedness efforts – and that policymakers will step up building security and learn how to encourage people to seek shelter quickly and safely. “There is a narrow window of opportunity to prevent and prepare for the next one,” he said.