Scientists raise red flag over dangerous trend in deadly heatwaves: 'The impacts are devastating'

A yearlong investigation into extreme heat by global climate experts highlights a dangerous trend: Climate change is fueling more intense and widespread heat waves than ever before.

What's happening?

A collaborative study by World Weather Attribution, the Red Cross Red Crescent Climate Centre, and Climate Central reveals just how much the changing climate has intensified deadly heat waves over the past year, and the results are deeply concerning.

Roughly 4 billion people, nearly half the global population, were exposed to at least 30 days of extreme heat during the study period. Researchers define extreme heat as "hotter than 90% of temperatures observed in their local area over the 1991-2020 period."

Just a few weeks after those startling statistics were released, the United States was enduring its first major heat wave of the summer. Several major cities experienced historic heat during the last full week of June. On June 24, during the peak of the heat, several cities set new record highs, including Raleigh, North Carolina, Philadelphia, New York, Boston, and Newark, New Jersey, when temperatures soared to 100 degrees or hotter. More than 160 million people were impacted by extreme levels of heat and humidity.

Why is an increasing number of extreme-heat days important?

Heat is now the most lethal weather threat in the U.S., according to the National Weather Service, killing more people over the past 30 years than any other hazard, more than twice as many as flooding. A study published in the Journal of the American Medical Association in 2024 also noted a worldwide increase in heat-related deaths, with U.S. deaths more than doubling from 1993 to 2023. Researchers last year revealed that heat waves increase the risk of preterm birth and health complications in infants.

"Exposure to extreme heat makes it difficult for our bodies to cool off, resulting in heat-related illnesses including heat cramps, heat exhaustion, and even fatal medical emergencies such as heat stroke," stated the authors of a Climate Central study on the increasing number of hotter-than-normal summer days.

What's being done about the threat of more days of extreme heat in our future?

Last year continued a disturbing trend: The past 11 years now make up the 11 hottest in recorded history. In the U.S., the eight warmest years have all come since 2012. The joint study noted that 2025 started with the hottest January on record and the lowest amount of Arctic sea ice ever seen in the Northern Hemisphere.

"This is not a surprise or an accident — the causes are well known and the impacts are devastating," say the authors of the study. "The continued burning of coal, oil, and gas has released and accumulated enough greenhouse gases to warm the planet by 1.3°C (over a 5-year average) — and by more than 1.5°C in 2024 alone — compared to pre-industrial times."

Our warming world is supercharging extreme weather events, including heat waves. Reducing the amount of heat-trapping gases being released into our atmosphere is crucial for the future of our planet.

"We need to quickly scale our responses to heat through better early warning systems, heat action plans, and long-term planning for heat in urban areas to meet the rising challenge," Roop Singh, a climate risk adviser at the Red Cross Red Crescent Climate Centre, said in a World Weather Attribution statement, per Fast Company.

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