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The 2025 Lancet Countdown on Health and Climate Change paints a stark picture: the world is getting hotter, and the health consequences are accelerating.

Between 2020 and 2024, 84% of the heatwave days people experienced each year would not have occurred without climate change. As a result, heat-related deaths have surged by 63% since the 1990s, now averaging 546,000 deaths annually from 2012–2021.

The impacts extend far beyond mortality. 123.7 million more people are experiencing moderate or severe food insecurity linked to droughts and heatwaves, while lost labour productivity from extreme heat reached an estimated US$1.09 trillion in 2024. Low- and medium-income countries are bearing the greatest economic burden, losing a larger share of their GDP to heat exposure.

These findings underscore a growing reality: extreme heat is becoming one of the most urgent and unequal threats to human health and wellbeing. The report calls for accelerated action to strengthen early warning systems, urban planning, and heat-health protection, particularly for the most vulnerable populations.

Developed by 128 experts from 71 institutions, the Lancet Countdown tracks 57 indicators of health and climate progress, providing an essential evidence base for governments, researchers, and communities confronting the heat crisis.

Explore the report and data