Climate change has made summer drought ‘at least 20 times more likely’

DAMIEN MEYER / AFP This photograph taken in Loireauxence, western France, on September 20, 2022, shows a bridge spanning the dry Loire river bed. – This summer was the second hottest on record in France with temperatures averaging 2.3°C above normal, a series of large-scale forest fires that devastated much of the southwest, and widespread drought, as well as several severe storms . (Photo by Damien MEYER / AFP)


A bridge over the dry bed of the Loire, in Loireauxence (Loire-Atlantique), September 20, 2022.

ENVIRONMENT – Climate change caused by human activity has dried up the northern hemisphere this summer “at least 20 times more likely”and continued warming would make these episodes more intense and frequent, scientists warn.

Such soil drought, which has affected Europe, China or the United States, is likely to occur about every 20 years with the current climate, versus about every 400 years or even less often without warming, according to the World researchers. Weather Attribution (WWA), a network of pioneering researchers in the attribution of extreme events to climate change, which publishes a study this Wednesday, October 5.

The summer drought has affected many European countries, starting with France, with dry rivers and restrictions in some locations. Parts of the United States or China were also affected.

The consequences were felt in the agricultural sector, with declining harvests and possible effects on already high inflation. This situation has also favored forest fires and has disrupted the production of electrical energy, especially hydraulic and nuclear energy.

Experts from the European Commission’s Joint Research Center estimated this summer that the drought was “The worst in at least 500 years”.

In the northern hemisphere (outside the tropics), human-induced climate change has caused droughts” much more likely”according to researchers from the WWA network, who work in prestigious institutions in Europe, the United States and New Zealand.

This probability has been increased by a factor “at least 20” due to the lack of soil moisture in the root zone, the part of the soil corresponding to 1 meter below ground and where the plants extract water to feed themselves. When this very important area is affected, we speak of an “agricultural” drought. Where “ecological”.

The probability of the event has been increased by a factor “at least 5” for surface soil moisture, which is only the top seven centimeters.

Warming since the start of the industrial age has already reached almost 1.2°C

“But as is often the case with quantities that are difficult to observe, the exact numbers are uncertain.”the authors warn. “The estimates of the influence of climate change in the study are conservative: the true influence of human activities is probably higher”says the WWA.

The warming since the beginning of the industrial age, which has been fueled by fossil fuels, has already reached almost 1.2°C, leading to a series of disasters. The Paris agreement aims to keep this warming below 2° and if possible close to 1.5°.

“The summer of 2022 has shown how human-caused climate change is increasing the risk of agricultural and ecological droughts in agricultural and densely populated regions of the Northern Hemisphere”stressed Sonia Seneviratne, a professor in Zurich, co-author of the study.

“We need to stop burning fossil fuels if we want to stabilize climate conditions and prevent these droughts from getting worse. They will become more frequent and intense with any increase in warming.”she warned.

The researchers also looked only at the Central and Western European region. The results are less spectacular: global warming linked to human activity has made surface drought 5 to 6 times more likely there and agricultural drought 3 to 4 times more likely, according to their calculations.

This difference does not mean that climate change has had less of an impact in Europe compared to the rest of the Northern Hemisphere, but rather reflects the methodological ease of better understanding events in a larger region.

“Usually we get stronger climate change signals in larger regions”explained Friederike Otto of Imperial College London, a co-author of the study, during a presentation to journalists.

“When you look at smaller regions, you find more daily climate variability in the data”While this effect is “attenuated” taking into account larger areas, he explained.

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