An international coalition of scientists is urging world leaders and the World Health Organization (WHO) to formally declare climate change a global health emergency after finding that extreme heat caused roughly three million deaths between 2016 and 2023. The appeal was issued on October 28, 2026, in the 10th annual Lancet Countdown on Health and Climate Change report, published just weeks ahead of the United Nations COP31 climate summit in November. Led by University College London in collaboration with the WHO and funded by the Wellcome Trust, the assessment brings together 146 researchers from more than 100 institutions across over 30 countries to track 54 health and climate indicators.

According to Inside Climate News, the researchers warn that health harms driven by planetary heating have accelerated much faster in the decade since the 2015 Paris Agreement was adopted than in the decade prior. While the landmark climate treaty was once praised by the WHO as the most important public health agreement of the century, continued reliance on fossil fuels and record greenhouse gas emissions have outpaced global preparedness.

"The evidence is undeniable: climate change is one of the greatest threats to health facing humanity," WHO Director-General Tedros Adhanom Ghebreyesus said in the report, noting that the impacts are already visible through worsening heat stress, extreme weather events, food insecurity, and infectious disease risks.

Escalating Heat Mortality and How It Is Measured

The report identifies extreme heat as the most prominent and measurable threat to human life. In 2023—the latest year with complete mortality data evaluated in the study—heat was linked to an estimated record 710,000 deaths worldwide. According to Phys.org, that annual toll exceeds global mortality figures typically associated with malaria or HIV, with 71.5% of those 2023 heat deaths attributed directly to human-caused warming, while The Straits Times reports the human-caused share at more than 70%.

Looking at broader multi-year trends, the research estimates an average of 540,800 heat-associated deaths annually between 2016 and 2023. The study attributes 68% of those deaths—approximately 369,900 per year—directly to climate change, up sharply from 55% (or 219,100 deaths per year) recorded between 2006 and 2015. Cumulatively, Marina Romanello, executive director of the Lancet Countdown at University College London, noted that the three million heat-related deaths recorded in the eight-year span since the Paris Agreement is roughly equivalent to the entire population of Wales being wiped out.

To determine the exact share of mortality linked to human activity, researchers compiled state-recorded heat mortality figures and subtracted the baseline deaths that epidemiological models indicate would have occurred in a world without anthropogenic warming, explained Professor Ollie Jay of the University of Sydney's Heat and Health Research Center.

Jay emphasized that mortality figures represent only "the tip of the iceberg," adding that "that iceberg is not melting, it's growing every year." Beyond fatal outcomes, prolonged exposure to high temperatures triggers acute heatstroke, severe heat exhaustion, kidney strain, disrupted sleep patterns, and the rapid worsening of underlying cardiovascular and respiratory conditions.

Drought, Infectious Disease, and Economic Strain

Beyond direct temperature extremes, the Lancet Countdown tracks destabilizing shifts in global water systems and agricultural stability. According to Deutsche Welle, the global land area affected by extreme drought grew more than 700% faster in the past decade compared to the preceding ten-year period. In 2025 alone, extreme drought affected more than half of the world's land surface for at least one month.

These severe water extremes directly threaten food and clean water supplies, driving widespread malnutrition and heightening the risk of waterborne and vector-borne infectious diseases. While the report highlights shifting infectious disease patterns as a critical global indicator, the published summaries focus on broad global risks rather than quantifying specific disease outbreaks within the United States.

The physical toll on workers is also creating severe economic instability. Working in extreme heat places outdoor laborers—particularly farmworkers and construction crews—at immediate risk of occupational illness and injury. In 2025, heat exposure wiped out 573 billion potential working hours globally. Over the past three years, reduced worker productivity has cost the global economy more than $1 trillion annually, reaching an estimated $1.07 trillion in lost potential income last year alone.

While lower-income nations in Africa and Southeast Asia bore the heaviest burden—losing between 3.2% and 5% of their gross domestic product (GDP) according to differing regional metrics cited in the report—developed economies are not immune. The Americas lost an estimated 1.5% of GDP to heat-related productivity declines, compared to 0.2% in Europe.

What an Official Emergency Declaration Would Change

It is important for readers to note that the call for a "global health emergency" is currently a scientific recommendation from the Lancet Countdown authors, not an official declaration enacted by the WHO or the United Nations. While the WHO holds the authority to declare a Public Health Emergency of International Concern (PHEIC) for acute outbreaks, researchers are advocating for a new, specialized WHO or UN instrument designed specifically for the long-term threat of climate change.

According to Romanello, a formal global health emergency framework would shift governments away from "responding to emergency after emergency." Instead, the proposed designation aims to establish a cohesive, long-term response that builds healthcare system capacity, strengthens disease surveillance, and expands early-warning infrastructure so countries can prevent mass-casualty events before they happen.

Alan Dangour, director of climate and health at the Wellcome Trust, stated that global leaders must change course by placing human well-being at the center of climate negotiations. Rather than measuring success strictly by carbon emissions targets or degrees thresholds, Dangour argued that policy outcomes should be evaluated by lives saved and public health metrics improved.

Despite the grim trajectory, the report notes areas of measurable progress. Since 2016, 56 of the WHO's 194 member states have adapted their public health and early-warning systems to better anticipate extreme weather events. In addition, global investment in clean energy reached $2.1 trillion in 2025, demonstrating that structural transitions are underway even as researchers push for faster intervention at the upcoming COP31 summit.

Frequently Asked Questions

Has the World Health Organization officially declared climate change a global health emergency?

No. The call for an emergency declaration is a formal recommendation made by the 146 researchers behind the 2026 Lancet Countdown report. While the WHO collaborated on the study and Director-General Tedros Adhanom Ghebreyesus endorsed its findings regarding health threats, neither the WHO nor its member states have formally enacted a binding emergency declaration or established the proposed international instrument yet.

How does extreme heat impact everyday health and US communities?

While the retrieved study summaries do not break down city-by-city US mortality figures, the report shows the Americas lost the equivalent of 1.5% of GDP due to heat-related productivity losses. Clinically, extreme heat prevents the human body from cooling itself efficiently, which can lead to heat exhaustion, potentially fatal heatstroke, chronic kidney damage among outdoor workers, lost sleep, and acute flare-ups of preexisting heart and lung diseases.

What would a coordinated global health response actually do?

Researchers are calling for a permanent international framework that centers health in climate funding and policy. In practice, this means expanding national heat early-warning systems, upgrading hospital resilience against extreme weather, monitoring shifting infectious disease zones, and protecting vulnerable outdoor laborers from hazardous working temperatures.

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