Heatwaves like the one Europe saw in 2003 could become the new norm in the coming years, researchers report.

These heatwaves are particularly deadly for the elderly, the sick, and the poor.

The 2003 heatwave saw temperatures in Europe reach 47.5 degrees Celsius (about 117.5 degrees Fahrenheit), and was one of the worst natural disasters of recent decades, claiming an estimated 45,000 to 70,000 victims in the space of a few weeks.

Forests burned, crops withered in the fields, and emergency wards in the cities were full to capacity. Globally, costs totaled around $13 billion.

Nevertheless, the public remains less aware of the risks of heatwaves than of other climate-related extremes. This is a problem, the new study in Nature Communications points out.


Since 2013, researchers from the Institute for Environmental Decisions at ETH Zurich and colleagues have systematically collected data on daily heat-related excess mortality for 748 cities and communities in 47 countries in Europe, Southeast Asia, Latin America, the US, and Canada.

The researchers used this dataset to calculate the relationship between the average daily temperature and mortality for all 748 locations. From this, they established each location’s ideal temperature, where excess mortality is at its lowest.

In Bangkok, for example, this value is 30 degrees Celsius, in São Paulo 23, in Paris 21 and in Zurich 18 degrees Celsius (80, 73, 69.8, 64.4 degrees Fahrenheit respectively).

Every tenth of a degree above this ideal value increases excess mortality.

“Not all heat is the same,” says lead author Samuel Lüthi, a doctoral student under David Bresch, professor for weather and climate risks at ETH Zurich. “The same temperature has a completely different impact on heat-related excess mortality in the populations of Athens and Zurich.”

This depends not only on the temperature, but also on physiology (acclimatization), behavior (long siestas in the middle of the day), urban planning (green spaces versus concrete), the demographic structure of the population, and the local health care system.

Using this ideal value, the researchers calculated how excess mortality would develop with an average global temperature increase of 0.7 degrees (the value in 2000), 1.2 degrees (the value in 2020), 1.5, and 2 degrees Celsius. They used five particularly powerful climate models, known as SMILEs (single-model initial-condition large ensembles).

Read the full article about deadly heatwaves by Eth Zurich at Futurity.