A staggering four billion people—more than half of the world’s population—experienced at least one additional month of extreme heat over the past year, according to a new report linking the surge in deadly temperatures directly to human-caused climate change.
From May 2024 to May 2025, vast regions across the globe suffered unprecedented spikes in heat levels, triggering widespread health emergencies, straining energy grids, reducing crop yields, and overwhelming healthcare systems. The findings were released by a coalition of experts from World Weather Attribution, Climate Central, and the Red Cross Red Crescent Climate Centre.
The researchers used peer-reviewed scientific methods to analyze the growing intensity and frequency of heat waves, concluding that climate change was the primary driver behind the surge.
“Although floods and cyclones often dominate headlines, heat is arguably the deadliest extreme event,” the report stated. “Its impacts are silent but devastating.”
The Hidden Toll of Heat Waves
While hurricanes and wildfires often receive more attention, experts emphasize that heat waves are deadlier and far more insidious. Unlike storms that leave behind visible destruction, heat kills quietly—especially affecting the elderly, chronically ill, low-income families, and those without access to cooling systems.
“Heat waves are silent killers,” said Friederike Otto, associate professor of climate science at Imperial College London and one of the report’s lead authors. “People don’t fall dead on the street in a heat wave. They die at home or in hospitals, often unrecognized as heat-related fatalities.”
Many of these deaths go unreported or are misclassified under other health conditions, such as heart attacks or kidney failure. This undercounting, scientists say, masks the real and growing threat posed by extreme heat.
Climate Change Doubled the Number of Extreme Heat Days
The report’s findings show a dramatic increase in the number of extreme heat days in nearly every country. The scientists analyzed historical climate data and compared it with current heat trends, factoring in emissions and greenhouse gas concentrations. Their conclusion: in most parts of the world, extreme heat days have at least doubled, and in some regions, tripled.
“This is no longer an anomaly—it’s the new normal,” said Dr. Andrew Pershing, director of climate science at Climate Central. “People everywhere are experiencing temperatures that were once rare, multiple times a year.”
From Asia to Africa, the Americas to Europe, heat waves have become increasingly intense and prolonged. In many cities, especially in low- and middle-income countries, basic infrastructure has struggled to cope.
Vulnerable Populations at Greatest Risk
The report highlights that the most vulnerable communities suffer the most during extreme heat events. Older adults, people with pre-existing medical conditions, outdoor laborers, and those living in informal settlements or poorly ventilated homes face significantly higher risks.
In places like Delhi, Karachi, Cairo, and Lagos, entire neighborhoods lack access to reliable electricity or cooling systems. Children in schools without fans, workers on construction sites, and patients in underfunded hospitals are all disproportionately affected.
“Heat does not impact everyone equally,” said Julie Arrighi, acting director at the Red Cross Red Crescent Climate Centre. “We see that those with the fewest resources are the ones bearing the heaviest burden.”
In several countries, energy demand surged so dramatically during heat waves that power grids failed, leaving millions without electricity during the hottest hours. Hospitals also reported spikes in admissions due to heat strokes, dehydration, and respiratory distress.
Global Food Systems Also Hit Hard
In addition to health and infrastructure, agriculture is taking a major hit. Prolonged exposure to extreme heat has damaged crops, reduced yields, and strained irrigation systems. Farmers in parts of India, Sub-Saharan Africa, and the southern United States have reported losses in staples like rice, wheat, and maize, raising fears of food insecurity.
“We’ve seen entire harvests lost to just a few weeks of abnormal heat,” said Dr. Tanisha Kumar, an agricultural scientist based in Hyderabad. “There’s no resilience left in the soil—it’s been exhausted by repeated climate shocks.”
Livestock deaths due to overheating and water scarcity are also on the rise, further affecting food supplies and rural livelihoods.
Urgent Need for Local and Global Action
The scientists behind the report emphasize that while adaptation measures are critical, only long-term global mitigation—especially the phase-out of fossil fuels—can prevent the most catastrophic outcomes in the future.
To help vulnerable communities survive current and future heat waves, the report recommends:
- Establishing early-warning systems to alert the public about upcoming extreme heat events.
- Providing cooling centers and shelters, particularly in densely populated urban areas.
- Improving building designs to incorporate ventilation, shading, and heat-resistant materials.
- Offering emergency medical services with trained personnel for heat-related health issues.
- Enforcing workplace safety laws, especially for outdoor and manual laborers.
- Planting trees and creating urban green zones to naturally reduce city temperatures.
“Adapting to the heat is essential,” Otto added. “But without strong climate policies to drastically reduce emissions, these heat waves will become even more intense and more frequent. Adaptation alone won’t be enough.”
A Call to Phase Out Fossil Fuels
Ultimately, the scientists say that only comprehensive mitigation efforts—especially a rapid and coordinated shift away from coal, oil, and natural gas—can limit future temperature extremes and prevent widespread climate-related suffering.
“Each tenth of a degree matters,” said Dr. Pershing. “If we don’t act now to reduce global emissions, we will be looking at heat events that make this past year seem mild.”
With global temperatures now hovering around 1.2°C above pre-industrial levels, the urgency of meeting the 1.5°C limit agreed upon in the Paris Climate Accord has never been greater. World leaders are being urged to treat extreme heat as a humanitarian and security emergency—not just an environmental issue.
Final Thoughts
This new report serves as a wake-up call to both governments and individuals. The impact of climate change is no longer a distant threat—it’s already reshaping lives across the globe. From increased deaths to failed crops, overloaded hospitals to energy blackouts, the rising heat is placing pressure on every corner of society.
Unless immediate steps are taken to both adapt and mitigate, the next 12 months may bring even more suffering than the last.
