Challenge summer heat – climate change: we are already adapting – knowledge


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The summer heat last year was exceptional: 2022 was the second warmest summer ever recorded in Switzerland. A new report now shows that fewer people died from the heat than was feared. Apparently we are learning to deal with the heat better and better.

The hottest summer ever recorded in Switzerland was exactly 20 years ago. The toll was high: up to around 1500 people died from the heat. We were unprepared at the time: we just didn’t really know how to behave when it’s really hot and how best to adapt our houses, villages and cities to protect ourselves from the heat.

Heat also affects young people


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Older people in particular are threatened by too much heat. Studies show that the heat can aggravate existing illnesses: cardiovascular problems, respiratory, kidney or even mental illnesses become so serious in extreme cases that they can lead to death.

But hot days are also a stress test for the body for younger people: the consequences are rarely fatal, but there is a wide range of at least unpleasant symptoms, from heart palpitations to heat strokes, digestive problems, swollen feet and hands.

We know more about heat

Heat waves and hot days are on the increase – measures to protect health are therefore becoming increasingly important. “People know better today than they did then. We also have better warning systems, such as those from MeteoSwiss,” says Martina Ragettli, Researcher at Swiss TPH, the Swiss Tropical and Public Health Institute in Basel. The epidemiologist deals with how environmental changes affect us humans.

How to measure who dies from heat?

On behalf of the Federal Office for the Environment (FOEN) and the Federal Office of Public Health (BAG), Martina Ragettli and her team analyzed the heat-related deaths over the last 23 years.

Whether a person actually died from heat, or would have died without the influence of a heat wave, must be estimated statistically. “In order to calculate heat-related deaths in 2022, for example, we used the last 10-year period to determine how many people died at which temperatures,” says the researcher.

To do this, her team took the mean daily temperatures and used them to calculate how high the risk is at a certain temperature. An example: At an average daily temperature of over 27 °C, which is considered “very hot”, the risk of 75-year-old people increases significantly and at 30 °C is about 1.5 times the risk of death at normal temperatures. In other words: At such temperatures, fatalities are to be expected.

fewer deaths

The federal government publishes the number of heat-related deaths each year. Last summer there were around 500 and thus significantly fewer than in 2015 (around 750). What is interesting is that the summer of 2022 was hotter, and yet fewer people died from the heat. From this, the researchers conclude that we are better able to deal with heat today.

It is about our behavior and structural measures. Air conditioning also plays a role. It is considered unlikely that these are physical adaptations.

Corona is involved

The new method makes it possible to distinguish heat-related deaths from pure excess mortality. This has become important since Corona, as there are also corona deaths in summer that are not due to the heat (see box).

Excess mortality, the old method


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Based on the number of deaths in the last five years, a range of expected deaths in a specific period is given. This expected value fluctuates throughout the year – and is generally higher in winter because people are ill more often then.

If more people die than is expected within a certain range, this is referred to as “excess mortality”. So far, this has been used to estimate how many people die from heat in a hot summer. The same goes for the winter.

Previously, winter excess mortality was usually attributed to seasonal influenza. Since the emergence of Covid-19, things have become more complex, especially in the summer because the effects of Covid-19 are believed to mix with other effects.

Specifically: People who are weakened by a Covid-19 illness (which can also be a long time ago) have a higher risk of dying from a heat-related death on hot days. Researchers suspect that this effect can be seen in the summer of 2022, because the excess mortality for the summer of 2022 could not be fully explained.

“Because temperature information is now also included, statements can also be made if more than one extraordinary event influences the death rate in summer,” says Martina Ragettli. The indicator also shows that people not only die on very hot days, but also on “moderately hot” days when the mean daily temperature is below 25 °C. Almost a third of all deaths occur on such days.

With the new indicator, long-term monitoring will be possible, which should allow measures to be taken against the heat, it is hoped.

Additional information

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