It’s February and I’m writing about… heat waves

I know, it’s the coldest weeks of winter here in the UK, but I’ve just had air conditioning installed in my bedroom in London because after enduring three heatwaves in three consecutive summers, my wife and I just couldn’t take it anymore. The fact that air conditioning is being installed in homes in Britain should tell you something. There is climate change, which is increasingly interfering with our ability to work.

This is also the result of a survey among German workers and the impact of heat waves across Germany. Using data from Germany’s largest public health insurer, AOK, which insured almost a third of all Germans between 2007 and 2020, the study looked at employees aged 25 to 59 and whether they had received a sick note from an official doctor (with the wonderful German name ‘Arbeitsunfähigkeitsbescheinigung’).

Below is a graph showing the increase in the number of people taking sick leave as the heatwave continues. By the way, the people most likely to take sick leave are those with pre-existing circulatory conditions, as would be expected. If you have heart problems, heat waves are particularly dangerous.

Increase in absenteeism due to illness per 1,000 employees as heat waves spread

Source: Klauber et al. (2025)

Whether people take sick leave during a heat wave obviously also depends largely on their profession. The scatter chart below shows the probability of sick leave by occupation, along with the average monthly salary in the occupation. People who work outside in sectors such as transport or logistics, agriculture and construction are more likely to receive sick leave. However, I have no idea why mathematicians, biologists and physicists so often take sick leave during a heat wave.

Chance of absenteeism due to illness per profession

Source: Klauber et al. (2025)

This data allows us to estimate the costs of heat waves to the economy. They estimate that a three-day heat wave will cost the German economy an estimated €32.2 million in ‘lost wages’ and increase healthcare costs by 0.22% for each day during the heat wave. In terms of GDP, this is all negligible. Yet it shows that as heat waves become more intense and frequent, we need to invest in adaptations such as air conditioning (where possible) to reduce losses to the economy and taxpayers.