Cleaner air in Europe causing hotter summer than anticipated

Europe’s summer and heatwave will be even hotter than feared. Regional climate models used by planners significantly underestimate summer heat because they don’t take into account the intensity of sunlight caused by falling air pollution, the study found.

“If models do not take into account changes in air pollution, they will underestimate the intensity of future heat waves even more than they underestimate average summer warming,” he says. dominic schumacher At ETH Zurich, Switzerland. “This is a problem because many European countries rely heavily on these simulations to plan for the future.”

Running global climate models requires a lot of expensive computer time, so researchers often only look at smaller regions so they can run more detailed models. These high-resolution regional models are typically trusted by governments because their predictions for specific locations are considered more accurate than global models.

“Regional models are used in many countries to inform future changes, so they should be able to better capture the observed warming,” Schumacher said.

But when he and his colleagues compared the summer warming observed in Europe between 1980 and 2022 with predictions from global and regional climate models, they found that regional models predicted actual warming by an average of 1°C. It turned out that this was an underestimate. The global model was better, but underestimated by about 0.5°C on average.

One explanation is that the model lacks changes in air circulation patterns that would bring more heat into the region. Once Schumacher excluded the effects of circulation changes, the global models largely matched the observed warming, but the regional models still underestimated the changes by more than half a degree on average.

The researchers then looked at what assumptions the model was making about sunlight intensity. They found that most regional models do not take into account the fact that sunlight intensity is increasing in Europe as air pollutant levels fall. Few models take this into account and match the observed warming.

“The main reason these regional climate models have not been able to reproduce this anthropogenic warming is because most of them assume that air pollution remains constant,” he said at the European Global Conference in Vienna, Austria. said Schumacher, who announced the discovery at a meeting of the Scientific Union.

The researchers conclude that this means regional models are underestimating by more than 2 degrees Celsius how much warmer European summers will be by 2100. The underestimation of heat waves is even more serious, Schumacher said. That’s because during heatwaves, skies are usually clear and there is even more sunlight than usual.

All regional models will be changed to take into account the reduction in air pollution, but this will take time, he said.

It has been suggested that the record rise in global temperatures over the past year or so is due in part to a faster-than-expected drop in air pollution due to rising greenhouse gas emissions. Schumacher said his team’s research didn’t shed any light on this question, but other studies presented at the conference found otherwise.

He also pointed out that air pollution is estimated to cause millions of deaths each year, and stressed that the team’s findings should not be interpreted as air pollution being a good thing.