Heat waves that persist for three days or longer have lasting effects on workers as medical and sick-leave costs stay high for up to four years
On summer days when the air feels heavy, even simple tasks take effort, and a colleague might call in sick with a headache. As the planet warms, heat waves are quietly reshaping when, how, and whether we work.
Existing evidence tends to focus on the most exposed workers, such as those in outdoor jobs in agriculture and construction, or on particularly severe outcomes like workplace injuries. However, high temperatures can trigger a variety of health problems and may affect even workers in supposedly low-risk office settings, especially if they are older or have pre-existing conditions. By focusing narrowly on specific occupations and acute incidents at work, we risk overlooking the broader impact of heat exposure on labor supply.
In our recent IZA Discussion Paper, we study how heat waves affect workers of all health backgrounds across the labor force. We focus on Germany, a country offering universal access to paid sick leave. Drawing on individual-level health insurance data, covering more than a decade of daily sick-leave records for about one-third of the working population, we trace how extreme temperatures translate into health-related absences.
On average, a single hot day (30 °C or more) raises new sick leave cases by about 3.5%, and after a week of persistent heat, the effect roughly triples. Our findings confirm that workers at higher risk of heat-related absence are concentrated in outdoor and physically demanding jobs. They tend to have lower incomes and limited flexibility in scheduling their work.
Yet, our study links heat waves to increased sick leave across all occupations, including business, education, and finance jobs. In these professions, the average risk of heat-related absence is lower, but compensating relatively large workforces during heat-induced sick leave translates into substantial aggregate costs. Moreover, in the health sector alone, we calculate that a three-day nationwide heatwave would lead to over 24,000 additional lost workdays, showing that heat exposure can strain personnel in critical infrastructure.
These heat impacts are not only short-term. Extreme temperatures provoke serious incidents, such as strokes or heart attacks, conditions that are less frequent but can lead to lasting declines in the ability to work. Correspondingly, our study indicates that heat waves lasting three days or more leave a lasting mark on workers: medical costs and sick-leave expenditures remain elevated for up to four years.
Climate change will shift temperature patterns, bringing more heat exposure but possibly also fewer cold days to temperate countries like Germany. While our study does not speak to the overall effects of global warming, it suggests that improved heat protection would reduce health-related absences, not only as temperatures rise but already today.
More broadly, the findings demonstrate that we must look beyond high-exposure occupations and short-term effects, both to identify those whose health, working conditions, or personal circumstances make them especially vulnerable, and to see where the aggregate effects fall across occupations. Only by taking this comprehensive view can we grasp both the unequal burdens heat imposes on workers and its broader consequences for labor supply.
© Hannah Klauber, Nicolas Koch, and Nico Pestel
Hannah Klauber is Economist at Potsdam Institute for Climate Impact Research (PIK), Germany
Nicolas Koch is Head of the "Policy Evaluation Lab" at the Potsdam Institute for Climate Impact Research (PIK), Germany, and IZA Research Fellow
Nico Pestel is Head of Division at the State Chancellery of North Rhine-Westphalia and IZA Research Fellow
Please note:
We recognize that IZA World of Labor articles may prompt discussion and possibly controversy. Opinion pieces, such as the one above, capture ideas and debates concisely, and anchor them with real-world examples. Opinions stated here do not necessarily reflect those of the IZA.
Related IZA World of Labor content:
https://wol.iza.org/articles/climate-change-and-the-allocation-of-time by Marie Connolly
https://wol.iza.org/articles/does-hot-weather-affect-human-fertility by Alan Barreca
https://wol.iza.org/articles/air-pollution-and-worker-productivity by Matthew Neidell Nico Pestel
Photo by Nicolas J Leclercq on Unsplash