New study: Increased risk of extreme heat waves

Last Friday, Gallargues-le-Monteux in southern France had a warm 45.9 degrees, which is the highest temperature ever measured in the country. In other parts of Europe, heat records were also broken. But is the extreme heat due to the ongoing climate change, or are it occasional weather events?

"The study shows very clearly that human impact on the climate has increased the likelihood of heat waves similar to what we have seen in Europe in recent weeks," says Erik Kjellström, professor of climatology at SMHI.

It is the international research network behind World Weather Attribution that looked at last week's French heat wave and compared the temperatures with what it looked like over 100 years ago, before humans began to affect the climate to a greater extent.

- Climate observations in France show that the risk of a similar heat wave is ten times greater today than it was 100 years ago, says Erik Kjellström.

- In addition, the heat waves have become more intense with temperatures four degrees higher than in the late 19th century.

The researchers behind World Weather Attribution are working to develop methods to scientifically determine whether climate change makes certain extreme weather events more or less likely to occur.

In the work, information on extreme weather events from climate observations is combined with results from climate models to investigate whether the conditions for different types of extreme weather events have changed due to human-caused global warming.

By combining temperature observations for southern France for the month of June, with calculations in different types of climate models, researchers conclude that the combined risk of similar heat waves occurring is at least five times as high today as it was 100 years ago.

The results of the study are still not scientifically examined, and the results must therefore be interpreted cautiously. But that there are now new scientific methods for estimating how much global warming actually affects the weather is very interesting and will be of great importance in the future, according to Erik Kjellström.

- If we can understand the differences in what has happened so far and how humans have affected the climate system, it can help us understand what future changes may look like, which is very important now that the climate is changing so rapidly, he says.