The 2026 Lancet Countdown on Health and Climate Change calls for climate change to be formally treated as a global health emergency. It estimates that heat was linked to a record 710,000 deaths in 2023, according to the World Health Organization, which collaborated on the report.
The report, released ahead of the COP31 climate summit, is the 10th edition of the annual assessment. It is led by University College London and involved 146 researchers from more than 100 institutions in over 30 countries.
Heat deaths climbing
Annual average heat-related deaths rose by nearly 36% in the years following the Paris Agreement compared with the previous decade, according to the WHO.
Heat was linked to the record 710,000 estimated deaths in 2023, and more than 70% of that burden was attributed to human-caused climate change. The figures are modelled estimates rather than counts drawn from death certificates.
Drought also spread. Extreme drought affected nearly 52% of the world's land for at least one month in 2025, the second-highest share on record, the report found.
Dr Diarmid Campbell-Lendrum, head of the WHO's Climate Change, Air Quality and Energy and Health Unit, said:
"Climate change is already harming health in every region of the world, and the evidence shows that many of these impacts are accelerating."
Fossil fuels still dominate
Despite those findings, the shift away from fossil fuels remains slow. Fossil fuels still supply more than 80% of global energy, according to the report.
The world's 100 largest oil and gas companies are on course to produce 150% more fossil fuels by 2040 than is compatible with limiting warming to 1.5C, the report said.
Cleaner air offers gains
The report also points to progress. Clean-energy investment reached a record US$2.1 trillion in 2025, about 82% more than was invested in fossil fuels, according to the researchers.
Cleaner air is estimated to prevent about 323,000 deaths a year in at least 77 countries where fossil-fuel air pollution has fallen since 2016.
What comes next
The report's central demand is that governments treat climate change as a health emergency rather than solely an environmental issue.
