Scientists said Friday that the deadly heatwave gripping large parts of Europe would have been virtually impossible without human-caused climate change, as a rapid attribution study connected the week’s record temperatures and dangerous nights to the warming driven by fossil fuel emissions.
The analysis by World Weather Attribution, an international group of climate scientists, found that the late-June heatwave over western Europe is the most severe ever recorded across the region it studied. The researchers said that in the climate of 1976, a year remembered for extreme European heat, temperatures like those seen this month would have been virtually impossible in June and highly unlikely at any time of year.
The study focused on the hottest three days and nights over the most affected area, alongside additional analysis of European capitals and hundreds of urban regions. It concluded that a comparable June heatwave would have been about 3.5°C cooler during the day in 1976 and about 2°C cooler in 2003, the year of one of Europe’s deadliest modern heat disasters. Nighttime temperatures would have been about 2.4°C cooler in 1976 and about 1.3°C cooler in 2003.
The findings underscore the central danger of the present heatwave: not only the peak afternoon temperatures, but also the persistence of extreme warmth overnight. Health authorities have repeatedly warned that tropical nights, when temperatures fail to fall below 20°C, can prevent the body from recovering from daytime heat stress. In parts of France, overnight temperatures have stayed above that threshold for more than a week, with some minimum temperatures close to 30°C.
World Weather Attribution said temperatures in the current episode were made much more likely and more intense by global warming, which has raised the planet’s average temperature by around 1.4°C above pre-industrial levels. The group said nighttime heat of this kind is now more than a hundred times more likely than it would have been in 2003, while daytime heat of comparable severity would still have been very rare two decades ago.
The heatwave has swept across France, Germany, Italy, Spain, southern Britain, Belgium, the Netherlands, Switzerland and other parts of Europe, forcing governments and local authorities to activate heat-health plans. The World Meteorological Organization said its European regional climate monitoring centre expected heat to affect large areas of western, central and southern Europe, with the focus shifting toward the Balkans. The affected zone includes countries from Portugal and Spain through France, Germany, Switzerland, Austria and Italy to parts of southeastern Europe.
The WMO said maximum temperatures above 35°C and nighttime minimums above 20°C were expected in many places, with some southwestern areas exceeding 40°C. It also warned of increased heat stress, wildfire risk and local severe thunderstorms, including hail. The British Met Office reported that the United Kingdom provisionally set a new June maximum temperature record, with 36.1°C recorded at Gosport in Hampshire on June 24.
In France, authorities reported dozens of deaths linked to people seeking relief in water during the heat, while schools, outdoor events, cultural sites and transport services were disrupted. Reuters reported that the heatwave had killed dozens across the region, disrupted power supplies and forced closures of schools and cultural landmarks. Italy experienced heat-related deaths, higher emergency-room admissions and power outages linked to surging cooling demand, while Belgium and the Netherlands also faced pressure on health and transport systems.
The scientists said the meteorological pattern behind the heatwave was not unusual enough by itself to explain the severity of the event. The study identified a circulation pattern broadly comparable with historical southern-flow episodes, in which hot air moves northward into western Europe. The decisive difference, the researchers said, is the higher climate baseline: the same broad atmospheric setup now produces much hotter temperatures than it did in the mid-20th century.
That distinction is important for public understanding of climate attribution. Heatwaves still require specific weather patterns, including high pressure, clear skies, weak winds and the movement of hot air masses. But in a warmer climate, those patterns operate on top of an already elevated temperature baseline. The consequence, scientists say, is that an event that once would have been unlikely or impossible can become a recurring summer threat.
The World Weather Attribution study also examined heat stress using wet-bulb globe temperature, a measure that combines temperature and humidity to assess the strain on the human body. The researchers said approximately 45% of the European urban regions analysed had broken, or were forecast to break, records for indoor heat-stress thresholds during the June 18-29 period. That finding points to a risk that extends beyond outdoor workers and athletes to people inside homes, schools, hospitals, care facilities and workplaces.
Heat stress is especially dangerous for older people, infants, people with chronic illnesses, outdoor labourers, homeless people and those living in poorly insulated or overcrowded housing. It can worsen cardiovascular and respiratory disease, increase dehydration and kidney strain, and reduce the body’s ability to cool itself through sweating. Because the health effects often accumulate over days, the full mortality impact of a heatwave is usually confirmed only after public-health data are reviewed.
Europe’s vulnerability is heightened by its building stock and infrastructure. Many homes, schools and public buildings were built to retain warmth during cooler seasons, not to keep interiors safe during prolonged heat. Air conditioning is less common than in hotter regions, and dense urban areas amplify heat through concrete, asphalt and limited nighttime cooling. Rail networks, roads, power grids and hospitals can also come under strain when temperatures exceed the ranges for which they were designed.
The study said heat risk is concentrated in cities, where the urban heat island effect combines with ageing buildings and socioeconomic inequalities. In practical terms, the same heatwave can have very different outcomes depending on whether residents have shaded streets, insulated homes, access to cooling centres, reliable healthcare, green space and the ability to avoid outdoor work during peak heat. Scientists and public-health experts say this is why heat policy increasingly has to combine emergency alerts with long-term urban redesign.
The current heatwave follows an unusually early and intense May event in western Europe. Copernicus Climate Change Service said western Europe experienced a severe heatwave during the second half of May, with the largest temperature anomalies across western France, England and Wales, where daily average temperatures reached more than 10°C above the 1991-2020 reference period. National and local records were broken for both daytime and nighttime temperatures.
The recurrence of major heat so early in the season has raised concern among forecasters because June is not historically the hottest month in western Europe. World Weather Attribution said June is warming faster than any other month across large parts of western Europe, and that the hottest daily temperatures are warming at around triple the rate of global warming. Nighttime temperatures are also rising faster than the global average, compounding health risk.
Europe is already the world’s fastest-warming continent. The European State of the Climate 2025 report by Copernicus and the WMO said Europe has warmed more than twice as fast as the global average in recent decades, with widespread above-average temperatures, shrinking snow and ice cover, marine heatwaves, drought stress and record wildfire impacts. The rapid warming of the continent makes extreme heat an increasingly central public-policy challenge rather than an exceptional weather concern.
The new attribution study also rejected El Niño as an explanation for this European event. While El Niño can raise global average temperatures, World Weather Attribution said the Pacific warming cycle did not contribute to the severity of the current heatwave over Europe. The researchers instead pointed to the long-term warming caused by greenhouse gas emissions, principally from burning coal, oil and gas.
Attribution science has become an increasingly important tool for interpreting extreme weather. Instead of asking whether climate change “caused” a single event in isolation, researchers estimate how warming has changed the probability and intensity of that class of event. In this case, the comparison with 1976 and 2003 showed that similar atmospheric conditions now produce heat that is substantially more intense, particularly at night.
The timing of the study gives it immediate policy relevance. Governments across Europe are already reviewing heat-health warning systems, school closure protocols, labour protections, hospital preparedness and the resilience of transport and energy networks. The findings suggest that planning based on historical heat records is no longer sufficient because those records were set in a cooler climate. Infrastructure designed around past extremes may be underprepared for the heat now emerging in ordinary summer circulation patterns.
Scientists said adaptation measures will need to include building retrofits, passive cooling, more urban trees and shaded public space, heat-safe school and care-home standards, targeted support for vulnerable residents, worker protections and stronger public-health surveillance. They also said adaptation alone cannot prevent further escalation if greenhouse gas emissions continue to warm the climate baseline.
The report’s central conclusion is that Europe is already experiencing climate impacts that exceed the limits of many existing systems. At approximately 1.4°C of global warming, the current heatwave has pushed temperatures, humidity and nighttime stress to levels that scientists say would have been virtually impossible in the climate of five decades ago. Without faster emissions cuts, they warned, similar or more severe heatwaves will become increasingly frequent and more damaging.
For European governments, the heatwave is therefore both an emergency and a forecast. The immediate task is to protect people through alerts, cooling access, medical preparedness and service adjustments. The longer-term task is to redesign cities, buildings, infrastructure and energy systems for a hotter climate while reducing the emissions that are making the extremes worse. The scientists’ analysis makes clear that the present heat is not simply a record-breaking weather episode; it is a measure of how far Europe’s climate risk has already shifted.
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