A new rapid attribution study by Vrije Universiteit Brussel (VUB) finds that human-induced climate change made the June 2026 heatwave in Belgium 3.9°C hotter and more than doubled the number of heat-related deaths. Of the estimated 1,181 deaths statistically linked to the extreme temperatures recorded between 17 and 28 June 2026, 665 - or 56% - would not have occurred without anthropogenic climate change. This is the first time heat-related deaths during a specific Belgian heatwave have been attributed to human-induced climate change.
The June 2026 heatwave was Belgium's deadliest on record. Over its twelve days, maximum temperatures in Uccle peaked at 35.5°C on 26 June. On the night of 24–25 June, the temperature did not fall below 24.1°C - the highest overnight minimum ever recorded during a Belgian heatwave since records began in 1892. Emergency services were overwhelmed: calls to the 112 emergency number reached nearly twice the usual daily volume on 26 June, and geriatric wards reached full capacity. According to provisional figures, 27 June was the second deadliest day of the 21st century in Belgium.
The study, published today as a rapid attribution report by researchers at VUB's Department of Water and Climate, is the first attribution of heat-related deaths to human-induced climate change for a specific Belgian heatwave. It uses established, peer-reviewed methods combining epidemiological models - which link daily maximum temperatures to mortality risk - with extreme event attribution methods that estimate how much warmer the heatwave was made by human-induced climate change. This rapid attribution study highlights that the health risks of climate change are already here today and fossil fuel emissions have caused the deaths of hundreds of Belgian citizens this June only.
Key findings include:
Climate change made the heatwave 3.9°C hotter. Human-induced climate change warmed the peak 12-day period by 3.9°C compared to a world without anthropogenic warming. For example, on the hottest day (26 June), Belgium's average daily maximum temperature would have reached 32.1°C instead of the observed 36.0°C in the absence of climate change.
Climate change more than doubled the heat-related deaths. The study estimates 1,181 heat-related deaths during the heatwave. Heat-related deaths thus equal about a quarter of all deaths recorded during the heatwave. Of these heat-related deaths, 665 deaths (56%) are attributable to human-induced climate change.
Women and older people bear the greatest burden. Women account for more heat-related deaths than men. People aged 85 and over account for half of all heat-related deaths (heat with or without climate change).
Wallonia — and Liège in particular — was hardest hit. The climate change attributable province death rate was highest in Liège (9–11 deaths per 100,000 inhabitants), followed by Hainaut and Namur (7–9 deaths per 100,000 inhabitants). Temperature anomalies exceeded 9.5-10°C above normal in parts of southern Belgium.
Belgium is warming faster than the global average. Europe has warmed about twice as fast as the global average since the 1980s. Heat extremes in western Europe have intensified even faster, due to diminishing air pollution and global circulation changes linked to climate change. This amplification pushed temperatures from the low-risk into the high-risk range of the temperature-mortality relationship, explaining the sharp increase in heat-related deaths.
Excessive heat disrupts the human body's normal functioning, aggravates pre-existing conditions, and can lead to serious complications such as heatstroke, dehydration, and organ failure. Dangerous heatwaves are being made more frequent and intense by climate change, primarily driven by the burning of fossil fuels like oil, coal, and gas.
Maxim Sleypen, Lead Author and researcher at VUB, said:
"Our research shows that without human-induced climate change, the June 2026 heatwave would have been nearly 4°C cooler. Of the almost 1,200 deaths we link to heat, more than half would not have occurred without this extra warming. This means that global warming is already costing lives in Belgium today. That is why every fraction of a degree of warming we avoid will save lives."
Emma Kuijt, Co-Author and researcher at VUB and UCLouvain, said:
"The burden of this heatwave was not shared equally. Older people, women, and communities in the most deprived areas suffered the most - likely exacerbated by factors beyond temperature alone, pre-existing health conditions coupled to socio-economic factors (housing with poor insulation, limited cooling capacity and many others). Understanding these inequalities is essential if we are to protect the most vulnerable."
Wim Thiery, Senior Author and Professor at VUB, said:
"Three compounding factors made this heatwave so deadly: Europe is warming twice as fast as the global average, heat extremes are intensifying even faster, and the risk of death rises steeply once temperatures pass a critical threshold. Every additional increment of global warming will push more heatwaves into that lethal range. Urgent cuts to fossil fuel emissions are not optional - they are a matter of life and death."
The findings come at a critical moment. The summer of 2026 was the warmest ever recorded in Belgium, and saw three officially declared heatwaves. The June event alone has been identified by World Weather Attribution as part of a wider European heatwave that would have been virtually impossible in a pre-industrial climate. As global temperatures continue to rise, events like this will become more frequent, more intense, and more deadly - unless mitigation is accelerated.
The authors call on policymakers to keep warming in line with the Paris Agreement, to substantially increase investment in adaptation - including heat action plans, early warning systems, and strengthened public health infrastructure - and to ensure that the most vulnerable communities are protected from the growing risks of extreme heat. Every degree of warming prevented translates into lives saved.
