This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study has found that a self-reinforcing interaction between temperature, soil moisture and atmospheric pressure is being triggered at high temperatures, making extreme heat waves 10% hotter than they would otherwise be. The study was published in Science Advances and led by the Potsdam Institute for Climate Impact Research (PIK) and the International Institute for Applied Systems Analysis (IIASA).
Local temperature records have been shattered in heat wave hot spots where "mega heat waves" have been increasing in frequency faster than more moderate extreme heat events in recent years. Notable examples include the 2022 heat wave in Europe, where temperatures in the U.K. topped 40°C (104 degrees Fahrenheit) for the first time, and the 2021 summer heat wave in the U.S. Pacific Northwest, where recorded temperatures reached 4.6°C above previous records.
The new study identifies an emerging physical process underlying the most extreme heat waves by using machine learning methods and statistical analysis. It found that most extreme heat events in the midlatitudes (for example, Europe, southern Russia and Mongolia, eastern and northwestern North America, northwestern India, the western coast of South America, central and southern Africa, and northern interior Australia) are being topped up by soil moisture, atmospheric pressure and temperature interacting to drive higher temperatures. High-pressure systems allow more solar radiation to reach the Earth's surface, heating up the land.
Likewise, as temperatures rise, soils gradually dry out, reducing their ability to cool the surface through evaporation, which causes the land to heat. "The two-way relationship between rising temperatures and drying soils has been understood for a while and is already factored into what we expect from a typical extreme heat event," explained PIK scientist and lead author Yinglin Tian. "But when we look at these mega heat waves that have been significantly outstripping previous temperature records, what we're seeing is that once you reach a certain temperature, all three factors—drying soils, high pressure and extreme heat—begin to interact and drive each other further in a way that we haven't understood before," Tian added.
The analysis shows that as the world has warmed from climate change, it has become more likely that the temperature threshold at which this dynamic is triggered is exceeded, and the reinforcing feedbacks begin to drive temperatures during a heat wave. In Europe, the feedback interaction is triggered at around 4 Kelvin above average summer temperatures, or roughly 29°C (84 degrees Fahrenheit). Between 1979 and 1983, the likelihood of temperatures in Central Europe exceeding this threshold was 6%.
In 2018–2022, it was 23%. This self-reinforcing dynamic is currently not well represented in the climate models that forecast extreme heat events. "If we're right and this interaction is making the most extreme heat events even hotter, it means we could be in store for more severe future heat wave risks than what is currently expected," said Kai Kornhuber, a co-author of the paper from IIASA and the Max Planck Institute of Geoanthropology.
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