Data reveal how this year’s back-to-back heatwaves are affecting populations and economies across Europe

Summer 2025 is roasting hot: these charts show why it matters

Data reveal how this year’s back-to-back heatwaves are affecting populations and economies across Europe

This year’s Northern Hemisphere summer brought back-to-back heatwaves in several countries.Credit: Antonio Denti/Reuters

The summer of 2025 is already shaping up to be a record-breaker. Two intense heatwaves have swept across Europe, causing hundreds of heat-related deaths, fuelling wildfires and pushing power systems to their limit — and more are on the way.

From mid-June to early July, Western Europe experienced its highest average temperatures for this period in decades, and the hottest June on record (see ‘Warmest June ever’). Temperatures soared above 40°C, and up to 46°C in Spain and Portugal, as a result of ‘heat domes’ — caps of high pressure that trap hot air in the atmosphere over an area, causing it to stay hotter for longer.

Source: European Centre for Medium-Range Weather Forecasts/Copernicus

Research suggests that heatwaves in the region are becoming much more frequent — London can now expect events like this every 6 years instead of every 60, according to a report published last month by Imperial College London’s Grantham Institute. “We’ll see more dramatic consequences for populations,” says Roman Hoffmann, a social scientist studying climate-related risks at the International Institute for Applied Systems Analysis in Laxenburg, Austria. “And more stress that will affect health, well-being, livelihoods and human security more broadly.”

Deadly conditions

Across 12 major European cities this year, about 1,500 of 2,300 estimated heat-related deaths — 65% — were driven by the extra heat resulting from fossil-fuel emissions, according to the Grantham Institute’s report (see ‘Lethal heatwaves’). The researchers compared real temperatures during the late-June 2025 heatwave with estimates of what temperatures would have been without human-caused climate change, then used health models to calculate the resulting heat-related deaths. The high temperatures were especially lethal for older adults, with people aged 65 and over making up nearly 90% of those who died.

Source: Grantham Institute report ***Climate change tripled heat-related deaths in early summer European heatwave***

Another study, which looked at the health effects of hot weather in Austria between 2015 and 2022¹, found that districts with older populations saw around 50% more deaths on very hot days than areas with younger populations did. The true toll could be even higher, because heat-related deaths are often undercounted, typically being recorded as the result of pre-existing conditions such as heart disease, says Hannah Schuster, a data analyst at the Vienna University of Economics and Business, who led the study. By 2050, many areas in Austria are expected to have twice as many hot days and many more older people — making heat-related deaths likely to rise unless action is taken to protect people from the heat, she adds.

Although countries with mild climates have long had systems in place to manage cold weather, they’re much less prepared for the growing challenge of extreme heat, Schuster says. This lack of readiness makes the first heatwave of the year especially dangerous, says Peter Klimek, a medical data scientist at the Complexity Science Hub in Vienna. In his own, unpublished, analysis of ten years of hospital and ambulance data from Austria, he found a 30% spike in diagnoses of circulatory, respiratory and mental-health conditions during heatwaves.

Klimek calls for better heatwave warning systems — particularly in hospitals and care homes — and long-term changes to cities, such as the creation of more cooling green spaces and modification of buildings to better dissipate heat.

Thousands displaced

Although it’s hard to track how many people are forced to leave their homes owing to extreme heat alone, data from the Internal Displacement Monitoring Centre (IDMC), a non-governmental organization in Geneva, Switzerland, show that thousands of people have been temporarily evacuated or displaced as a result of wildfires that occurred during this year’s heatwaves in Europe.

“This year is already record-breaking when it comes to wildfires,” says Ivana Hajžmanová, the global monitoring manager at the IDMC. Not all wildfires are directly caused by climate change, but increasingly hot and dry conditions help fires to spread faster and burn for longer. In June and July, wildfires swept across southern Europe, disrupting a hospital and airport in Sardinia, and Turkey saw 50,000 evacuations as a result of fires in Izmir, the country’s largest ever wildfire displacement event. Similarly, the region near Athens recorded 14,000 displacements in early June, IDMC figures show (see ‘Fleeing fires’).

In 2024, about 45 million people worldwide were forced to leave their homes owing to weather-related disasters, including floods, wildfires and droughts, IDMC data suggest. The Institute for Economics & Peace, a think-tank based in Sydney, Australia, projects that by 2050, 3.4 billion people will live in countries facing severe ecological threats (in 2022, it was 2 billion). The ability to relocate from hotter to cooler locations on a more permanent basis is often limited to those with more resources, education and opportunities, Hoffmann says.

Using data from 72 countries, Hoffmann and his colleagues found that drought and dry conditions cause more people — especially in rural farming areas — to move long-term within their own countries². Working-age people mainly leave poorer regions, whereas in wealthier countries, older adults are most likely to move — often for retirement.