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Human-Caused Climate Change Increased Drought Likelihood by Over 20 Times

A picture of dry crops
Credit: Keagan Henman/ Unsplash

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The 2022 Northern Hemisphere summer was one of the hottest ever recorded in Europe with over 24,000 heat-related fatalities, and brought intense heatwaves to parts of China and North America. It was also very dry, and the resulting drought caused widespread water shortages, wildfires and crop failures leading to higher food prices, as well as impacts on electricity supply.

An international team of climate scientists led by the research group of Sonia Seneviratne, Professor for Land-​Climate Dynamics at ETH Zurich, now analysed the possible influence of climate change on this extreme weather event. Their study published by the World Weather Attribution group estimates that human-caused climate change made soil moisture drought conditions in the Northern Hemisphere at least 20 times more likely, threatening crop production and adding further pressure to food prices and food security.

Intense agricultural and ecological droughts

For their study, the researchers analysed soil moisture levels in June, July and August 2022, across the whole Northern Hemisphere, excluding the tropics. They also focused on Western and Central Europe, which experienced particularly severe drought with substantially reduced crop yields. Soil moisture dryness in the top metre of soil, known as the root zone where plants extract water, is often referred to as agricultural and ecological drought.

Human-caused climate change made agricultural and ecological droughts in the North Hemisphere extratropics at least 20 times more likely, the researchers found. They calculated that drought conditions like this summer’s can be expected around once in 20 years in today's climate. If humans had not warmed the planet, the agricultural drought conditions in the Northern Hemisphere would only have been expected around once in 400 years or less.

In the case of West-Central Europe, human-induced climate change made the agricultural and ecological drought about 3 to 4 times more likely. This does not mean that climate change has had less influence on Europe than elsewhere in the Northern Hemisphere; the different sizes of the regions mean the results cannot be directly compared.

The 2022 summer has shown how human-induced climate change is increasing the risks of agricultural and ecological droughts in densely populated and cultivated regions of the North Hemisphere”, Seneviratne says.

High temperatures as human-made driver

The main factor driving the heightened agricultural and ecological drought risk were increasing temperatures, with changes to rainfall relatively less important. Climate change increased temperatures across the Northern Hemisphere to such an extent that a summer as hot as this year’s would have been virtually impossible without human-induced climate change, the scientists found.

“The results of our analysis also give us an insight on what is looming ahead”, says Dominik Schumacher, postdoc in Seneviratnes research group and first author of the study. “With further global warming we can expect stronger and more frequent summer droughts in the future”.

“That’s why we need to phase-out the burning of fossil fuels if we want to stabilise climate conditions and avoid a further worsening of such drought events”, concludes Seneviratne.

Reference: Schumacher D, Zachariah M, Otto F, et al. High temperatures exacerbated by climate change made 2022 Northern Hemisphere soil moisture droughts more likely. World Weather Attribution. 2022.

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