It’s February, and I am writing about… heat waves

I know, it’s the coldest weeks of winter here in the UK, but I just had an air conditioning unit installed in my bedroom in London because after suffering through three heat waves in three consecutive summers, my wife and I just couldn’t bear it anymore. The fact that houses in the UK get air conditioning installed should tell you something. Climate change is here, and it is increasingly interfering with our ability to work.

This is also the result of a study among German workers and the impact of heat waves across Germany. Using data from Germany’s largest public health insurer, AOK, which insures close to a third of all Germans from 2007 to 2020, the study looked at workers aged 25 to 59 and whether they got an official doctor’s sick notice (which has the wonderful German name ‘Arbeitsunfähigkeitsbescheinigung’).

Below is a chart that shows the increase in the number of people taking sick leave as the heat wave extends. By the way, the people most likely to take sick leave are people with pre-existing conditions of the circulatory system, as could be expected. If you have heart problems, heat waves are particularly dangerous.

Increase in sick leave per 1,000 workers as heat waves extend

Source: Klauber et al. (2025)

Of course, whether people take sick leave in a heat wave also significantly depends on their occupation. The scatter plot below shows the likelihood of taking sick leave by occupation, together with the average monthly salary in the occupation. People who work outside in areas like transport or logistics, agriculture and construction are more likely to take sick leave. However, I have no clue why mathematicians, biologists, and physicists are so likely to take sick leave in a heat wave.

Likelihood of sick leave by profession

Source: Klauber et al. (2025)

This data allows us to estimate the cost to the economy from heat waves. They estimate that a three-day heatwave costs the German economy an estimated €32.2m in ‘lost wages’ and increases health care costs by 0.22% for each day in the heatwave. In GDP terms, all of that is negligible. Still, it shows that as heat waves become more severe and more frequent, we need to invest in adaptation like air conditioning (where possible) to reduce the losses to the economy and taxpayers alike.