‘TOO HOT TO HANDLE’: Climate Change Added 30 Days of Extreme Heat Globally

By Francis Allan L. Angelo

Human-caused climate change has added an average of 30 extra days of extreme heat for 4 billion people—roughly half the global population—over the past 12 months, according to a new global analysis released ahead of Heat Action Day on June 2.

The report, titled Climate Change and the Escalation of Global Extreme Heat, was produced jointly by World Weather Attribution (WWA), Climate Central, and the Red Cross Red Crescent Climate Centre. Drawing on data from 247 countries and territories, the report combines peer-reviewed climate attribution science with urgent calls for local and global heat response planning.

“All 67 major extreme heat events in the past year were made more likely by climate change,” the report states.

The study period, from May 1, 2024, to May 1, 2025, included Earth’s hottest year on record and the hottest January ever recorded. In that span, 4 billion people experienced at least 30 days of extreme heat—defined as daily temperatures hotter than 90% of historical observations for their region from 1991 to 2020.

“In the past year, climate change added an extra month of dangerous heat for four billion people. That’s half of the people on Earth, a staggering result,” said Dr. Mariam Zachariah, a climate researcher at Imperial College London and part of the WWA team.

In many tropical regions, the added number of extreme heat days exceeded 100—quadruple the global average. Aruba led all territories with 187 total days of extreme heat; 142 of them were attributed to climate change.

“This study needs to be taken as another stark warning. Climate change is here, and it kills,” said Dr. Friederike Otto, co-lead of WWA. “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.”

Heat Attribution Science

Researchers used Climate Central’s Climate Shift Index (CSI) and ERA5 data to compare observed temperatures with modeled scenarios of a world without human-caused climate change. The result quantifies how much more likely and intense heat events have become.

“All 67 extreme heat events identified over the past year were made more likely by human-caused climate change,” said Dr. Kristina Dahl, Vice President for Science at Climate Central.

Among the most extreme examples:

• The May 2024 heatwave in the Pacific Islands was made at least 69 times more likely due to climate change.
• A Central American and northern South American event in late August was at least 24 times more likely.
• A December 2024 event stretching across Central and West Africa was 15 times more likely.
• In South Sudan, a February 2025 heatwave forced school closures after children collapsed in classrooms.

WWA’s criteria identified four specific heatwaves for in-depth analysis. In Central Asia, temperatures were 10°C hotter than they would have been without global warming. In the Mediterranean and South Sudan, the report found such heat events would have been virtually impossible without climate change.

Impacts and Harm

Despite the mounting danger, the health and societal impacts of extreme heat remain underreported. Vulnerable populations—including outdoor workers, elderly residents, pregnant individuals, low-income groups, and those with chronic illnesses—bear the brunt of the heat.

“In Juba, South Sudan, dozens of schoolchildren collapsed due to heat,” said Dr. Zachariah. “This triggered a two-week nationwide school shutdown, which directly impacts education and long-term development outcomes.”

Dr. Lisa Patel, pediatric hospitalist and executive director of the Medical Society Consortium on Climate Health, highlighted heat’s cumulative impact on health, citing increased hospitalization for dehydration and heat-exacerbated birth complications. “Heat can cause long-term organ damage, especially in those repeatedly exposed,” she said.

High humidity levels further increase danger by hindering the body’s natural cooling process. Bernadette Woods Placky, Chief Meteorologist at Climate Central, noted that humidity’s compounding effect is especially deadly but often overlooked in measurements and responses.

‘Silent Killer’

One of the report’s central concerns is the widespread underreporting of heat-related deaths and illnesses. Many fatalities are mistakenly attributed to secondary conditions such as cardiovascular or renal failure, obscuring the true public health toll.

“We found that while people may recognize heat as a growing threat, many don’t see themselves as personally at risk,” said Karina Izquierdo, Urban Advisor for Latin America and the Caribbean at the Red Cross Climate Centre. “In Nepal, 60% of survey respondents recognized heatwaves as serious, but many said they were ‘used to the heat’”.

This normalization of danger weakens preventive actions and delays urgent adaptation strategies.

Adaptation Is Not Enough

The report lays out a multi-level strategy for addressing heat impacts:

• Individual actions: Staying hydrated, adjusting activity levels, and using cooling techniques like wet towels.
• Household measures: Installing reflective roofs, improving insulation, and ensuring ventilation.
• Community and city-level strategies: Creating Heat Action Plans (HAPs), establishing cooling centers, and using heat hotspot maps.
• Urban planning: Greening cities, providing shaded areas, and upgrading public infrastructure.
• Policy and legal reforms: Enacting heat safety laws, revising building codes, and integrating cooling into social protection programs.

However, the report emphasizes that these adaptations are stopgap measures without systemic change.

“There is good news. We know exactly how to stop heatwaves from getting worse: restructure our energy systems to be more efficient and based on renewables, not fossil fuels, and create more equal and resilient societies,” Dr. Otto said.

The year 2024 was the first in which average global temperatures stayed 1.5°C or more above pre-industrial levels for the entire year. Scientists warn that the 2°C threshold—considered a dangerous tipping point—could make events like the 2025 Central Asia heatwave an annual occurrence.

Without rapid decarbonization, current adaptation strategies will likely be overwhelmed.

“This is not a surprise or an accident,” said Dr. Zachariah. “It is a direct consequence of continued fossil fuel use and increasing atmospheric emissions”.