Over the past year, nearly half of the global population experienced an additional month of extreme heat due to human-driven climate change, according to a recent scientific study.
The report highlights the widespread health and environmental impacts of continued fossil fuel use, particularly in developing regions where the effects often go underreported. Scientists stressed the urgency of implementing early warning systems, public awareness campaigns, and urban-specific heat action plans to help communities better prepare for rising temperatures.
“With each barrel of oil burned and every tonne of carbon dioxide released, more people suffer from intense heat waves,” said Friederike Otto, a climate scientist at Imperial College London and co-author of the study.
The research was conducted by scientists from World Weather Attribution, Climate Central, and the Red Cross Red Crescent Climate Centre. It was released in advance of Heat Action Day, observed on June 2 to raise awareness about heat-related illnesses like heat exhaustion and heat stroke.
Researchers analyzed data from May 1, 2024, to May 1, 2025, and defined “extreme heat days” as those hotter than 90% of temperatures recorded between 1991 and 2020 at specific locations. They then compared this data to climate simulations representing a world without human-induced global warming.
Their findings were striking: nearly four billion people — 49% of the global population — endured at least 30 extra days of extreme heat. The team documented 67 heatwave events during the year, all of which showed clear signs of being influenced by climate change.
Aruba, a Caribbean island, was the most affected location, experiencing 187 extreme heat days — 45 more than would have occurred in the absence of global warming.
The study comes after 2024 was declared the hottest year ever recorded, overtaking 2023. January 2025 also set a new record as the warmest January on record. On a five-year average, global temperatures are now 1.3°C above pre-industrial levels. In 2024 alone, that figure exceeded the 1.5°C limit outlined in the Paris Agreement.
Researchers also pointed out a significant data gap in heat-related health impacts across lower-income countries. While Europe recorded over 61,000 heat-related deaths during the summer of 2022, many deaths elsewhere are underreported or wrongly attributed to other health conditions like cardiovascular or respiratory issues.
To tackle the crisis, the study urges investment in climate-resilient infrastructure, improved building designs with better shading and ventilation, and changes in public behavior — such as limiting outdoor activity during peak heat.
However, the authors made clear that adaptation alone will not solve the problem. To prevent further escalation in the severity and frequency of heatwaves, rapid global action to eliminate fossil fuel use is essential.
