Lancet Countdown: Heat-Related Deaths Up Nearly 36% in Decade After Paris Agreement

The 2026 Lancet Countdown on Health and Climate Change, released today, Oct. 28, estimates that annual average heat-related deaths worldwide rose by nearly 36% in the decade after the Paris Agreement entered into force, compared with the decade before.

The report is the 10th in the series. It is led by University College London, developed in collaboration with the World Health Organization, and tracks 54 indicators. Per the report, 146 researchers from more than 100 institutions in more than 30 countries contributed.

The heat numbers

Heat was linked to an estimated 540,800 deaths per year from 2016 to 2023. The report attributes 68% of those, or 369,900 a year, to human-caused climate change. In 2006–2015, the share was 55%, or 219,100 a year.

2023 was the worst year in that window. Heat was linked to a record 710,000 estimated deaths, and the report says 71.5% of them were driven by climate change. It says that toll exceeds deaths from malaria or HIV. Across 2016 to 2023, the report estimates climate change caused almost 3 million heat deaths.

These are modeled estimates, not death-certificate counts. The attribution to climate change comes from comparing observed temperatures with what the authors model would have occurred without human-caused warming.

Drought and country detail

The report says extreme drought affected nearly 52% of the world's land for at least a month in 2025, the second-highest level on record. It also cites satellite analysis suggesting that since 2003, 80% of the world's land has faced significant shifts toward drier or wetter groundwater conditions.

India gets specific figures. People there were exposed to more than 2,600 hours a year in 2016–2025 in which heat posed a moderate or higher risk of heat stress during moderate outdoor activity. That is more than 200 hours above the 1990s annual average. Indians also lost an estimated 64 hours of sleep a year to hot nights between 2021 and 2025, about three hours more than in 1986–2005.

What the report says is working

The findings are not all negative. Global clean energy investment hit a record $2.1 trillion in 2025. Countries that cut fossil fuel-related air pollution are estimated to be preventing thousands of premature deaths each year. More countries have adopted national health adaptation plans and climate-informed early warning systems.

"Climate change is already harming health in every region of the world, and the evidence shows that many of these impacts are accelerating," said Dr. Diarmid Campbell-Lendrum, head of WHO's Climate Change, Air Quality and Energy and Health Unit. "At the same time, this report demonstrates that climate action is a health intervention."

Marina Romanello, executive director of the Lancet Countdown, said: "These numbers point to a clear emergency."

The authors call for climate change to be formally recognized as a global health emergency. They also want health built into emissions, adaptation and financing decisions.

Europe's summer

A separate set of two peer-reviewed papers in Nature Health puts a number on this summer's heat in Europe. Researchers at Imperial College London modeled deaths in 854 cities across 30 countries from June through August. They estimated 50,391 heat-related deaths, of which 32,619 they attribute to the added heat from burning coal, oil and gas.

That is about 71% above the previous worst summer in the same dataset, 29,480 deaths in 2022. The cities hold roughly 40% of the population of the countries studied. The authors say the total is an undercount because it excludes a deadly May heat wave and everything outside those cities.

Italy, France, Spain and Germany had the highest tolls. About a third of the deaths fell between June 17 and July 1, when temperatures ran 5.3°C (9.5°F) above normal. Western Europe's summer was about 2.9°C (5.2°F) above the 1991–2020 average, with some days more than 12°C (21.6°F) above normal in some countries.

The method has limits the authors acknowledge. Clair Barnes, the lead author, said the team can be "quite confident" in calling 2026 "likely to have been the worst on record for heat-related mortality across much of Europe." The researchers say the approach has produced estimates broadly in line with those later published by national health authorities.

Barnes also pointed to infrastructure. "Much of Western and Northern Europe, our infrastructure is just not designed to cope with the sort of temperatures that we are seeing now," she said.

The policy backdrop

The Lancet report lands as governments prepare for COP31, which is scheduled to begin Nov. 9 in Antalya, Türkiye. A UN assessment earlier this month found that current policies could lead to 2.8°C of warming this century and beyond. CNN reported that another UN report days before the Europe study warned the 1.5°C target has effectively slipped out of reach.

The Paris Agreement asked countries to hold warming well below 2°C and preferably to 1.5°C. By the report's own accounting, the decade since has brought rising heat deaths alongside record clean energy spending.

Whether COP31 will act on the authors' request for a formal global health emergency designation is an open question. Delegates have not announced a decision on it.