Europe's scorching summer and heatwaves are set to be even hotter than feared. A study presented at a recent European Geosciences Union meeting suggests that regional climate models relied upon by policymakers have significantly underestimated the intensity of summer heat, as they did not account for the increased sunlight due to reduced air pollution.
In July 2023, in Athens, Greece, a woman cools down with a bottle of water. Image source: Louisa Gouliamaki/AFP/Getty
"If models do not account for changes in air pollution, they will underestimate the intensity of future heatwaves, potentially even more severely than underestimating the average summer warming," said Dominik Schumacher, a researcher at the Swiss Federal Institute of Technology in Zurich. "This is problematic because many European countries heavily rely on these models for future planning."
Running global climate models requires a significant amount of costly computer time, so researchers often focus on smaller regions to run more detailed models. These high-resolution regional climate models are typically relied upon by governments because their predictions for specific regions should be more accurate than global climate models.
"Many countries use regional climate models to predict future changes, and they do perform well in capturing warming," Schumacher said.
However, when Schumacher and colleagues compared observed European summer warming from 1980 to 2022 with predictions from global and regional climate models, they found that the regional climate models on average underestimated actual warming by over 1 degree Celsius, while global climate models underestimated by around 0.5 degrees Celsius.
One explanation is that these models overlook changes in air circulation patterns, which are bringing more heat to the region. When researchers accounted for the impact of these factors, global climate models aligned closely with observed warming, but regional climate models still underestimated by over 0.5 degrees Celsius on average.
Next, researchers examined the models' assumptions about sunlight intensity. They found that most regional climate models did not consider the fact that sunlight intensity in Europe is increasing as air pollution levels decrease. A few models that included this factor aligned with observed warming.
"These regional climate models fail to reproduce this anthropogenic warming primarily because most models assume air pollution levels to be constant," Schumacher said.
This means that regional climate models are underestimating the extent of summer warming in Europe by 2100. The research team's conclusion is an underestimation of over 2 degrees Celsius. Schumacher noted that the underestimation of heatwaves is even more severe, as clear skies and increased sunlight during heatwaves are typical.
The research team believes that all regional climate models will now be adjusted to account for reduced air pollution, but this will take time.
For more information on the related paper: https://doi.org/10.5194/egusphere-egu24-18153
