A new analysis shows that human-caused climate change made 67 extreme heat events between May 2024 and May 2025 more likely including record-shattering heatwaves in the Mediterranean, Central Asia, and South Sudan. All 67 events either broke temperature records, caused serious damage, or both.
Using the Climate Shift Index, researchers found that every country and territory experienced more extreme heat days due to climate change. In 195 countries, the number of such days has at least doubled compared to a world without global warming. Nearly 4 billion people half the world’s population faced an extra month of extreme heat over the past year.
The report, compiled by Climate Central, World Weather Attribution, and the Red Cross Climate Centre, points to a troubling global pattern. In Aruba, 187 extreme heat days were recorded in the last year more than four times the expected amount without climate change. The Federated States of Micronesia saw 57 extra extreme heat days, the highest climate-added total of any nation. The United States experienced 46 extreme heat days, 24 of which were directly attributed to climate change.
The most climate-influenced event was a record May 2024 heatwave in Pacific islands, which scientists estimate was made at least 69 times more likely by rising global temperatures.
The study used 30 years of historical temperature data (1991–2020) to identify extreme heat days those in the top 10% of observed temperatures. While some scientists note this is a relatively broad definition, it aligns with the temperature range where heat-related illness and mortality begin to rise.
According to the authors, the planet has already warmed by 1.3°C compared to preindustrial times (based on a five-year average), with 2024 marking the first year global temperatures consistently exceeded the 1.5°C benchmark. Without immediate action to phase out fossil fuels, future heat-related harms could grow far worse.
Extreme heat is a silent but deadly threat. It burdens the human body, aggravates existing health conditions like cardiovascular and respiratory diseases, and increases the risk of heatstroke and death. Vulnerable populations including outdoor workers, people without access to cooling, and those with chronic illnesses are especially at risk.
In response, the International Federation of Red Cross and Red Crescent Societies will host Heat Action Day on 2 June, focusing on global awareness of heat-related health risks. The campaign will promote recognition of symptoms like heat exhaustion and stroke and share prevention tips from agencies like the CDC.
The message is clear: extreme heat is no longer a distant threat. It’s here, it’s intensifying, and it demands urgent climate action and preparedness.