In brief

·  New research reveals how much rising global temperatures could amplify mortality risks if past hazardous weather patterns occur again.

·  The weather patterns that produced past extreme heat events in Europe could kill tens of thousands more people if repeated in today’s hotter climate.

·  Mitigating further global warming and preparing health systems, homes, and communities for the hottest days ahead can reduce deaths from extreme heat events.

The weather patterns that produced some of Europe’s most extreme heat waves over the past three decades could prove far more lethal if they strike in today’s hotter climate, pushing weekly deaths toward levels seen during the COVID pandemic, according to a Nov. 18 study in Nature Climate Change.

“We showed that if these same weather systems were to occur after we’ve trapped a lot more heat in the atmosphere with greenhouse gases, the intensity of the heat waves gets stronger and the death toll rises,” said lead study author Christopher Callahan, who completed the research as a Stanford Doerr School of Sustainability postdoctoral scholar and recently joined the Indiana University faculty.

Global average temperatures in recent years have approached 1.5 degrees Celsius above pre-industrial levels and about 0.7 degrees above the 2003 average, when a heat wave killed more than 20,000 people across Europe. This year, 2025, researchers estimated thousands of people may have lost their lives because of extreme heat during the fourth-hottest summer in European history.

Using a combination of artificial intelligence and statistical techniques from economics, Callahan and colleagues estimate that 2003-like weather patterns could cause 17,800 excess deaths across the continent in a single week against the backdrop of today’s climate, compared to 9,000 with no global warming. At 3 degrees Celsius above pre-industrial levels, their modeling shows weekly excess deaths from a 2003-like weather system could reach 32,000.

Recipe for Disaster
Deadly heat waves in Europe have repeatedly followed the stalling of a high-pressure system, or “heat dome,” over land already parched from months of low rainfall.

In the summer of 2003, an extreme version of this combination held temperatures around 38 degrees Celsius (100 degrees Fahrenheit) for two weeks straight across much of Western Europe. In France, refrigerated trucks stored bodies as morgues reached capacity. The temperatures were so extreme that the event essentially broke conventional probability calculations, which suggested that without climate change it might be a one-in-a-million-year event.