Lancet Countdown Estimates Nearly Three Million Climate-Linked Heat Deaths Since 2016

A new international climate and health assessment estimates that human-caused climate change contributed to nearly three million heat-related deaths worldwide between 2016 and 2023. The 2026 Lancet Countdown report, released on October 28, calls for climate change to be formally recognised as a global health emergency, arguing that rising health risks are outpacing measures to address them.

The report was prepared by 146 researchers and monitors 54 indicators spanning exposure to climate hazards, health-system preparedness, emissions, finance and policy. It estimates that heat was associated with an average of about 540,800 deaths annually during 2016–2023, of which 68% were attributable to human-driven climate change. Those figures are modelled estimates rather than a count of deaths individually certified as climate-related.

For 2023 alone, researchers estimated approximately 710,000 heat-related deaths, with more than 71% attributable to human-caused warming. The researchers compare observed heat exposure and mortality with a counterfactual world without the additional warming caused by human activity. Such attribution depends on statistical models and underlying mortality data, so the estimates should not be treated as exact counts.

The study also calculates that heat exposure reduced potential labour income by approximately $1.07 trillion worldwide in 2025. It reports that more than half of the world's land experienced extreme drought for at least one month that year. These indicators show the economic and environmental dimensions of heat-related risks, although they measure different phenomena and should not be combined into a single mortality estimate.

The report identifies progress alongside those harms. Investment in clean energy reached approximately $2.1 trillion in 2025, and researchers estimate that cleaner air has helped avoid around 323,000 deaths annually in countries where pollution from fossil fuels declined. More governments have also introduced climate-informed health plans and warning systems. The authors say these improvements remain insufficient to offset the growing health burden.

The report's recommendation is not an announcement that the World Health Organization or national governments have already declared a new formal emergency. Rather, the researchers are urging institutions to make health outcomes a central measure of climate policy and to coordinate a more sustained response. The findings are being presented ahead of the COP31 climate negotiations in November.