Moderate Temperatures Also Cause Death – Not Only Extreme Heat


Recent analyses by Swiss TPH show that not only heat waves, but also moderately hot temperatures, contribute to heat-related fatalities. On behalf of the Swiss federal government, Swiss TPH now monitors heat-related deaths in Switzerland on an annual basis. This monitoring provides a long-term record of the effects of climate change on health and helps to identify adaptation measures.

High temperatures and heat waves pose a risk to human health. Heat-related ailments include heat exhaustion, heat stroke, and the exacerbation of pre-existing conditions such as cardiovascular, respiratory, renal or mental illnesses. The European Environment Agency identifies heat stress as the biggest direct climate-related threat to human health in Europe. 

After the exceptional summer of 2003, heat-related deaths in Switzerland were recorded selectively after each heat-wave summer, for example for the hot summers of 2015, 2018 and 2019. Starting from the summer of 2023, Swiss TPH will now monitor heat-related deaths annually. Swiss TPH carries out this monitoring on behalf of the Federal Office for the Environment (FOEN) and the Federal Office of Public Health (FOPH).

"The new monitoring of heat-related deaths also includes days with moderately hot temperatures, so that the influence of less pronounced heat periods can be taken into account," said Martina Ragettli, project leader of the heat monitoring project at Swiss TPH. "Additionally, this monitoring enables us to differentiate heat-related deaths even when multiple extraordinary events, such as the COVID-19 pandemic, simultaneously impact mortality during a single summer."

Deaths occur even in moderately hot temperatures

The first report on the new Swiss TPH monitoring was published today by the FOEN (link to report). The report presents comprehensive analysis covering the period from 2000 to 2022, including data on the heatwave summer of 2022, the second warmest summer since records began in 1864. In 2022, there were 474 heat-related deaths, accounting for 1.7% of all deaths during the warm season between May and September. These fatalities affected individuals aged 75 and above, with 60% being women. The regions surrounding Lake Geneva, Ticino, and northwestern Switzerland recorded the highest number of heat stress-related deaths during the summer of 2022.

Swiss TPH's analyses further demonstrate that even moderately hot temperatures, defined as summer temperatures below 25°C, can lead to fatalities, not exclusively during heat waves. "On such days, the risk of heat-related death is lower than on extremely hot days, but they are much more frequent," said Ragettli. "Therefore, people with health problems and the in particular the elderly should adapt their behaviour even on moderately hot days."

Heat adaptation and protective measures reduce mortality risk

The researchers also observed a slight decrease in the risk of heat-related mortality on hot days. "This suggests that some adaptation to the increasing heat has taken place in recent years," explains Ragettli. In recent years, the federal government and the cantons have implemented various measures to raise awareness of heat-related health risks and to reduce heat stress in cities and buildings.

However, with climate change leading to more frequent and intense heat waves and hot days, the risk of heat-related deaths persists. Thus, the need for measures to protect health from heat are becoming increasingly important.

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