A report partnered with the United Nations and the World Health Organization on Wednesday estimated a record 710,000 people globally died from heat in 2023.
For the first time, more than seven in 10 of those fatalities were attributable to human-caused climate change, according to the Lancet Countdown report. The document analyzed global trends across 54 indicators linking climate change and health.
The authors said health harms from climate change are accelerating. Heat exposure in 2025 caused the loss of 573 billion potential work hours, costed at $1.07 trillion, the report found. Heat-related deaths have increased by nearly 36% since the 2015 Paris Agreement compared to the prior decade.
The global area affected by extreme drought has grown more than 700% faster than it did between 2006 and 2015, with droughts affecting 51.8% of global land for at least one month in 2025. The report also examined the link between rising temperatures and rainfall patterns to dengue transmission, finding that conditions suitable for transmission by Aedes albopictus mosquitoes increased by 24% between the 1981 to 1990 and 2016 to 2025 periods.
Expanding fossil fuel extraction is threatening catastrophic health risks, the authors said. The world’s 100 largest oil and gas companies plan to produce 150% more fossil fuels by 2040 than is compatible with limiting warming to 1.5 degrees Celsius above pre-industrial averages.
The UN World Meteorological Organization separately warned that atmospheric levels of carbon dioxide and other greenhouse gases reached record highs in 2025, locking in more long-term temperature increases.
However, clean energy investments and climate action are starting to deliver health benefits. Cleaner air from reduced fossil fuel pollution is preventing an estimated 323,000 deaths a year in 70 countries. Clean energy jobs grew 2.3% in 2024, and global clean energy investment reached a record $2.1 trillion last year.
About one in four countries now have a national plan to adapt health services to climate change, up from 14 WHO member states in 2015. Wealthy nations accounted for 55% of climate and health laws in 2025, compared to 2% in developing countries.
The authors called for formally recognizing climate change as a global health emergency ahead of the UN COP31 climate conference in Antalya, Türkiye.