Lancet Countdown Estimates 710,000 Heat-Related Deaths in 2023, Urges Global Health Response

A new global assessment of climate change and health estimates that heat was associated with 710,000 deaths worldwide in 2023, with more than 70% of that toll attributable to human-caused climate change. The 2026 Lancet Countdown report was presented on October 28 at a health and climate conference scheduled to begin at 13:00 UTC, ahead of the COP31 climate summit.

The report's findings are statistical estimates of heat-associated mortality, not a count of death certificates identifying heat as the immediate cause. Researchers compared conditions under observed warming with estimates of what would have happened without human-caused climate change. The assessment also examines the decade after the Paris Agreement entered into force against the preceding decade.

Across 2016–2023, researchers estimated an average of about 540,800 heat-related deaths each year, with roughly 68% attributable to climate change. The World Health Organization said annual average heat-related deaths were nearly 36% higher in the period following the Paris Agreement than in the preceding decade.

The report describes impacts extending beyond mortality. It estimates that extreme heat cost the world 573 billion potential working hours and US$1.07 trillion in potential earnings in 2025. It also reports that 51.8% of the world's land experienced extreme drought for at least one month that year, underscoring the combined effects on workers, food production and water security.

The assessment also identifies progress. Clean-energy investment reached approximately US$2.1 trillion in 2025, while some countries reduced deaths associated with fossil-fuel air pollution. More governments have prepared health-system adaptation plans and introduced early warning systems, although access and funding remain uneven.

Researchers called for climate change to be formally recognized and addressed as a global health emergency, with public health incorporated into emissions policy, adaptation planning and international financing. This is a recommendation by the report's authors; it is not an announcement that the WHO has issued a formal Public Health Emergency of International Concern declaration.

The Lancet Countdown is an international research collaboration involving 146 experts and 54 indicators. Its conclusions highlight both the growing estimated health burden and the potential benefits of reducing pollution and improving preparedness.