A staggering 4 billion people—half of the world’s population—experienced at least 30 additional days of extreme heat over the past year due to human-induced climate change, a new international study revealed Friday.

Published ahead of Heat Action Day on June 2, the report was compiled by experts from World Weather Attribution (WWA), Climate Central, and the Red Cross Red Crescent Climate Centre.

Key Findings

• Between May 2024 and May 2025, billions were exposed to extreme heat — temperatures hotter than 90% of historical observations in their region — directly attributed to climate change.
• All 67 major heatwaves documented globally in the past year were intensified by climate change.
• The number of extreme heat days has at least doubled in 195 countries and territories due to fossil fuel-driven global warming.
   

Expert Warnings

• Dr. Friederike Otto (WWA co-lead, Imperial College London): “This study is a stark warning. Climate change is here, and it kills. We must transition to efficient, renewable energy systems.”
• Mariam Zachariah (Imperial College): Described the findings as “staggering,” citing serious societal effects from heat-related illnesses, death, crop failures, productivity loss, and transport disruption.
• Roop Singh (Red Cross Red Crescent Climate Centre): Urged expanded early warning systems, heat action plans, and resilient urban planning.
• Dr. Kristina Dahl (Climate Central): “Heat is the deadliest consequence of climate change. We can now quantify how fossil fuel emissions are reshaping global daily temperatures.”
   

Global Call to Action

• The authors stress the urgent need for:
• Stronger heat action policies and early warning systems
• Nationwide monitoring of heat impacts
• Long-term adaptation planning in urban and rural areas
   

This report adds to the mounting scientific consensus that climate-driven extreme heat is not a future threat, but a current and deadly reality, with billions already affected.

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