This June, a historic, day-and-night heatwave has seared across Western and Southern Europe, bringing dangerous triple-digit temperatures and oppressive humidity to millions of people. A groundbreaking rapid attribution study released Friday by the international climate research collective World Weather Attribution (WWA) has delivered a definitive conclusion: this record-breaking extreme heat event could not have occurred without the influence of human-caused climate change.
The research, which analyzes the current heat dome-fueled heatwave that began spreading across the continent on June 18, draws stark comparisons between modern climate conditions and historical heat patterns. Scientists found that an identical heat event would have been virtually impossible to occur in the climate conditions that existed 50 years ago, in 1976. Compared to the baseline of just 20 years ago, this type of extreme heat is now 200 times more likely to occur.
To put these temperature shifts in context, the study team compared current temperatures to two major historic European heat events, 1976 and 2003, which were previously regarded as extreme benchmarks. Researchers estimate that a comparable heatwave in 1976’s cooler climate would have registered 3.5°C (6.3°F) lower during daytime hours and 2.4°C (4.3°F) lower at night. Even as recently as 2003, the same event would have been 2°C (3.6°F) cooler during the day and 1.3°C (2.3°F) cooler after sunset.
“The increase in temperatures was so dramatic that we would have expected to have never seen this event in the 1976 climate,” explained lead author Theodore Keeping, a climate scientist at Imperial College London’s Centre for Environmental Policy. “And it would also still have been very, very rare, even 23 years ago in 2003.”
WWA, a European-based collaborative network of climate scientists focused on linking extreme weather to climate change, has pioneered rapid event attribution studies since 2015. Their work examines how much of the increased risk of extreme events can be traced back to climate change driven by fossil fuel emissions. While the organization’s rapid studies have not completed full peer review, they rely exclusively on methodology that has already passed peer review, giving their findings broad scientific credibility. For this analysis, the team combined observed on-the-ground temperature data with weather forecast modeling to assess the full scope of the heatwave.
Beyond just air temperature, the study measured combined heat stress, a metric that accounts for both temperature and humidity and directly reflects dangerous strain on the human body. The analysis found that 45 percent of the 850 cities across 30 European countries included in the study have already broken, or are on track to break, all-time records for heat stress. Keeping noted that this combination of extreme heat and high moisture makes the current event far more dangerous than a dry heatwave, as it impairs the body’s ability to cool itself through sweating.
In the researchers’ assessment, this marks the most severe heatwave ever recorded in Northwestern Europe, and the most intense humid heat event ever documented in the region.
Europe is uniquely vulnerable to this type of extreme heat, due to its faster rate of warming compared to the global average. Data from the EU’s Copernicus Climate Change Service confirms that Europe has warmed at twice the global average rate since the 1980s, making it the fastest-warming continent on Earth. A 2023 WWA study found that roughly 1,500 excess deaths were tied to a climate change-fueled European heatwave last summer alone.
Much of the continent also lacks critical infrastructure to handle sustained extreme heat. Most residential and public buildings across Western Europe do not have widespread air conditioning, leaving millions without a reliable way to cool down after the sun sets. Unusually high overnight temperatures during this heatwave have prevented people from recovering from daytime heat exposure, amplifying health risks.
In response to the crisis, national weather agencies across France, Italy, Spain, the United Kingdom and other impacted countries have issued the highest-level red heat alerts. Major sporting events, school sessions, public transit operations and tourist attractions have been restricted or canceled to reduce heat-related risks. France, which has born the brunt of the current heatwave, recorded its hottest all-time national temperature this week, and has already reported 40 drowning deaths as people flocked to bodies of water to find relief from the heat.
Remarkably, researchers found that the current El Niño ocean warming cycle in the Pacific has had no measurable impact on this specific heat event. This June’s heat also follows on the heels of an unprecedented record-breaking heatwave that hit Europe in May 2024, marking an early start to the extreme heat season that typically does not arrive until July and August.
Some outside climate experts say the WWA study may actually understate the role of climate change in driving the extreme heat. Michael Mann, a prominent climate scientist at the University of Pennsylvania who was not involved in the research, noted that the study’s findings are reasonable, but similar attribution analyses have consistently underestimated how much climate change amplifies extreme heat events.
“If anything, this latest assessment — and all similar assessments — are actually underestimating the role that climate change is playing here,” Mann said, pointing to his own separate research on climate change-driven heat stress amplification in North America.
For Keeping and the WWA team, the findings of the study send a clear message to policymakers and communities: extreme heat events like this are no longer rare anomalies, and urgent action is needed both to adapt to unavoidable warming and cut the carbon emissions that are driving climate change.
“We need to expect them to happen. They’re only going to become more frequent in the near term,” Keeping said. “We also need to address the source of climate change as well. And that is very simply carbon emissions from burning fossil fuels.”