Scientists are very cautious about the hypothesis of a direct link
There is no evidence that catastrophic hurricanes are directly linked to climate change
Severe storms destroyed many facilities and factories.
AFP
Many families were displaced due to the destruction of their homes due to severe storms.
AFP
The rubble of houses damaged by severe storms.
AFP
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Did climate change cause the catastrophic hurricanes that recently hit the United States?
Although the conditions for the formation of these climatic phenomena may be enhanced by warming, scientists are very cautious about the hypothesis of a direct link.
Scientists have proven that climate change this year played a role in a heat wave in the northwest of the United States, or in the floods that inundated large areas of Germany and Belgium.
However, the specific phenomenon of tornadoes is one of the most difficult to analyze.
"In recent years, we have recorded an upward trend in favorable conditions," for the formation of tornadoes in the midwestern and southeastern United States, climatologist John Allen told AFP. Stronger during the winter.
But he points out that it is misleading to attribute this event to climate change.
And a professor of climatology at Florida State University, James Elsner, draws an important comparison: “Although the number of car accidents tends to increase due to fog, any accident that may occur in the presence of fog may be due to a completely different cause.
To determine this cause, an investigation is necessary, as the science (attribution) of extreme events to climate change is on an upward trend.
But such a study would take a long time if it was conducted.”
In the meantime, can climate change be said to increase the number of tornadoes, by creating favorable conditions for them?
John Allen answers: "The available evidence seems to point in this direction.
But I don't think we can finalize it."
In its latest report issued by its experts in August, the Intergovernmental Panel on Climate Change noted that there is “a low degree of confidence in establishing a link between climate change and localized phenomena, such as tornadoes.
This applies to (recorded trends), as well as to future (speculations).
What changes are recorded?
The average annual number of tornadoes in the United States, which occur frequently during the spring, has not increased over the past years, as it remained at around 1300.
"Most of the months there are even declines in these hurricanes," says Jeff Trapp, chair of the department of atmospheric sciences at the University of Illinois.
But he points to an exception posed by the months of December and January, which recorded an increase in tornadoes, during the past three to four decades.
This trend was observed, especially in the southern United States, which fits with a "possible explanation related to climate change."
In fact, the two ingredients required for tornadoes to form are hot and humid air near land, and winds blowing in opposite directions at points of different altitudes (the so-called vertical shear winds).
However, today, “there is an increase in the probability of hot days during cold periods, which may support the formation of tornadoes and tornadoes,” according to Jeff Trapp.
"Hurricanes appear to be concentrated within a narrower time scale," explains researcher Chiara Lupuri, a researcher at Columbia University.
And when there is a tendency to record a greater number of them at the same time, and this has consequences in terms of the extent of the damage.”
Finally, scientists note a geographical expansion of these phenomena towards the east of the American region called “Tornado Alley” (the hurricane corridor), which transfers them to states such as Arkansas, Mississippi or Tennessee, all of which were damaged by final hurricanes last week.
future expectations
The problem with the researchers studying tornadoes is that they are transient and small to the extent that they do not appear on the climate models usually used.
Thus, scientists are forced to content themselves with studying the evolution of conditions that may be conducive to their formation.
A study published in early November showed that for each additional degree of Celsius warming, the probability of creating favorable conditions for extreme weather events (including hurricanes) increased by between 14 and 25% in the United States.
However, this does not mean that tornadoes will form every time these conditions meet, but rather that their probability is very small.
The lead author of the study, Chiara Lupuri, explains that "this constitutes a kind of extreme, what we can reach with each additional degree of global warming."
And Jeff Trapp notes that another study to be published later shows that "tornadoes may become more powerful in future climatic conditions."
To reach this conclusion, the researchers relied this time on an already recorded event and analyzed the impact of future climatic conditions on it.
But extremely violent tornadoes will remain "rare events", according to Trapp's predictions.
James Elsner sums it up: “We're only just beginning to understand the link between climate change and what we call localized severe storms," but in the next five to 10 years we will see real progress.
The average annual number of tornadoes in the United States, which are frequent during the spring, has not increased over the past years, as it remained at around 1,300.
A study published in early November showed that for each additional degree of Celsius warming, the probability of creating favorable conditions for extreme weather events (including hurricanes) increased by between 14 and 25% in the United States.
Scientists have proven that climate change this year played a role in a heat wave in the northwest of the United States, or in the floods that inundated large areas of Germany and Belgium. However, the specific phenomenon of tornadoes is one of the most difficult to analyze.
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