Half the world has experienced an extra month of extreme heat due to climate change, study says

Half of the world's population suffered an additional month of extreme heat last year due to human-induced climate change, a study published Friday (30) revealed.

The findings underscore how the continued burning of fossil fuels harms health and well-being across all continents, with particularly underappreciated effects in developing countries, the authors said.

“With every barrel of oil burned, every tonne of carbon dioxide released and every fraction of a degree of warming, heatwaves will affect more people,” said Friederike Otto, a climatologist at Imperial College London and co-author of the report.

The analysis, by academic group World Weather Attribution, NGO Climate Central and the Red Cross Red Crescent Climate Centre, was published ahead of World Heat Action Day on June 2, which this year highlights the dangers of heat exhaustion and heat stroke.

To assess the influence of global warming, researchers analyzed the period between May 1, 2024 and May 1, 2025. They defined “extreme heat days” as those in which temperatures exceeded 90% of those recorded in a given location between 1991 and 2020.

Using a peer-reviewed model, they compared the number of such days to a simulated world without anthropogenic warming.

The results were staggering: approximately 4 billion people (49% of the world's population) experienced at least 30 additional days of extreme heat.

The team identified 67 episodes of extreme temperatures throughout the year and found the hallmarks of climate change in all of them.

The Caribbean island of Aruba was worst hit, with 187 days of extreme heat, 45 more than expected in a world without warming.

The study was conducted after a year of record global temperatures: 2024 was the hottest year on record and January 2025 was the hottest January.

On a five-year average, global temperatures are now 1.3°C above pre-industrial levels and will not exceed the symbolic 1.5°C threshold set by the Paris Climate Agreement until 2024.

The report also highlights the lack of data on the health impacts of heat in low-income regions.

Europe recorded more than 61,000 heat-related deaths in summer 2022, but comparable numbers are scarce elsewhere.

The authors emphasized the need for early warning systems, public education and adapted heat action plans for cities. They also considered it essential to improve building design and avoid strenuous activities during peak heat hours.

Still, adaptation alone will not be enough. The only way to halt the growing severity and frequency of extreme heat is to rapidly phase out fossil fuels, the authors warned.

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