Its 2026 report attributes more than 70% of those estimated deaths to human-caused climate change and estimates $1.07 trillion in potential income losses from heat in 2025, adding to its call for a coordinated health response.
Heat was linked to an estimated record 710,000 deaths worldwide in 2023, the latest year with complete mortality data, the 2026 Lancet Countdown finds. The researchers attribute more than 70% of those deaths to human-caused climate change. They also estimate that heat caused $1.07 trillion in potential income losses in 2025 by reducing the hours people could work.
The tenth annual report brings together 146 researchers from more than 30 countries, led by University College London in collaboration with the World Health Organization (WHO). Inside Climate News described the findings on 28 October. The report says lower-income countries, which contributed relatively little to climate change, bear a disproportionate share of its health harms.
Analysis
For the death estimate, researchers used mortality data from 129 countries to model how deaths vary with temperature worldwide, then combined those results with annual mortality estimates. To estimate the share linked to human-caused warming, they compared modeled deaths under observed temperatures with modeled deaths under temperatures that would have occurred without that warming.
The model assumes the relationship between temperature and deaths stayed constant over time. The researchers say this could overestimate later deaths if people adapted to heat, or underestimate them if people became more vulnerable.
The income figure is an estimate based on potential work hours lost to heat, not a tally of wages workers actually missed. The report identifies Southeast Asia and Africa, and the agriculture and construction sectors, as hardest hit in livelihoods.
Among participants who stayed on treatment, Lilly says its highest retatrutide dose reduced A1c by 2.2 percentage points versus 1.8 for Ozempic after 80 weeks, and weight by 20.9% versus 9.4%. The results describe that group, not everyone enrolled.
The Paris Agreement was adopted on 12 December 2015 and entered into force on 4 November 2016. Comparing 2016–2023 with 2006–2015, the report finds that annual average heat-related deaths rose nearly 36%. That is a comparison of average death counts, not a measure of how quickly deaths rose.
For drought, the report uses a different measure: it says the area affected by extreme drought grew more than 700% faster after the agreement entered into force than it did in 2006–2015. Its latest drought finding concerns 2025.
The report also estimates that from 2016 to 2023, cleaner air prevented 323,000 deaths a year in countries where fossil fuel-related air pollution fell, with leading gains in China and the United States. Increased deaths elsewhere offset those gains globally, it says.
The report’s authors ask WHO and its member states to formally recognize climate change as a global health emergency. They propose using existing emergency mechanisms and creating a new WHO instrument to connect early warnings, health-system preparations, emergency response and funding. WHO describes the declaration as the authors’ proposal. It says it is already using early warnings and emergency operations, and has operated a response team for the expected health effects of the ongoing El Niño since September 2026.
Inside Climate News warned on 28 October that an El Niño intensified by climate change was likely to bring further harmful events in 2026 and 2027. Lancet Countdown executive director Marina Romanello urged governments to prioritize early warnings and equip health systems to respond to potentially lethal extremes. Those are warnings about future risks, unlike the report’s estimates for past years.
At the climate conference known as COP31, scheduled for November 2026, participants are expected to review climate goals. Diana Picon Manyari, international climate senior director at Health Care Without Harm, wants health professionals included in the talks, along with attention to preparing health systems for climate impacts, reducing emissions and making financing easier to access.
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The review warns that reversing nature loss and meeting 23 targets by 2030 require rapidly accelerated action. Countries also agreed a voluntary route for additional donors to signal interest before COP18, while leaving the form of a post-2030 financial mechanism for that conference in 2028.
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The journal’s chief editor says new articles are held out of MEDLINE and PubMed Central during a review, preventing their appearance in PubMed while the review continues.
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