The decade since the Paris Agreement entered into force has been the deadliest decade for heat on record — and the researchers who measure that toll are now demanding the world treat it accordingly. The 2026 Lancet Countdown on Health and Climate Change, announced today with WHO collaboration, produced by 146 researchers from 71 collaborating institutions across more than 30 countries, finds a record 710,000 heat deaths in 2023 — the highest single-year figure the report series has ever documented — and that average annual heat deaths in the post-Paris decade are nearly 36% higher than in the decade that preceded it. More than 70% of those deaths are directly attributable to human-caused climate change, according to the report’s climate attribution analysis. The report calls for climate change to be formally recognized as a global health emergency.

The call comes at a decisive institutional moment: COP31, the UN climate conference, is scheduled to open in Antalya, Turkey, on November 9, 2026. The Lancet Countdown has historically timed its global annual release to land in the weeks before COP negotiations begin. This year, what it is releasing is both a surveillance record and an institutional demand — not merely documenting what warming has cost, but naming the response mechanism the researchers believe the numbers now require.

Eleven Years After Paris: 36% More Deaths Per Year, Not Fewer

The Paris Agreement entered into force on November 4, 2016. The Lancet Countdown was established that same year specifically to measure whether the world’s most ambitious diplomatic climate commitment was delivering measurable health benefits. Ten years of data have now accumulated. The answer the 2026 report delivers is unambiguous: heat mortality has accelerated, not slowed, since Paris.

The 710,000 heat-linked deaths recorded in 2023 are the highest single-year figure in the Lancet Countdown series, and they follow a trend line that has only moved upward. The 2025 Countdown — covering data through 2024 — had already found prior Lancet Countdown heat averages running 63% higher than in the 1990s, averaging 546,000 per year between 2012 and 2021. The 2026 report extends and sharpens that picture. The post-Paris decade is measurably deadlier in per-year terms than the decade that preceded it, and 2023 was its worst single year.

That deterioration has unfolded during a period of significant geopolitical change. The United States — the country with the largest historical share of cumulative greenhouse gas emissions — withdrew from the Paris Agreement effective January 27, 2026, after re-entering in 2021 under the Biden administration. As of the 2026 Lancet Countdown’s publication, the US is not a party to the agreement whose health outcomes the report is measuring. The absence of the world’s largest historical emitter from the Paris framework is a structural gap the report’s accountability framing implicitly registers — though the aggregate mortality trend it documents reflects a decade of emissions decisions made under that framework and before it.

Professor Marina Romanello, Executive Director of the Lancet Countdown at University College London, said that progress on addressing the mortality trend “has been too slow, too small, and isn’t reaching those who need it most.” The report’s call for a formal global health emergency designation is, in this context, less a rhetorical escalation than a proportional response to what a decade of surveillance now shows.

How Science Produces the 70% Attribution Figure

The claim that more than 70% of 2023’s heat deaths are attributable to human-caused climate change is not an estimate in the colloquial sense. It is the output of a specific scientific methodology — counterfactual climate modeling and Fraction Attributable Risk (FAR) analysis — that has become increasingly precise and increasingly consequential since it was formally introduced in a 2004 Nature paper analyzing the 2003 European heatwave.

The FAR approach works by running climate models under two scenarios: the actual world, with human greenhouse gas emissions included, and a counterfactual world from which those emissions are removed. The fraction of heat mortality that would not have occurred in the counterfactual scenario — the deaths that required anthropogenic warming to happen — is the Fraction Attributable to human activity. Applied at the global annual scale across the Lancet Countdown’s full suite of climate indicators, that fraction exceeds 70% for 2023’s global heat toll.

This methodology also explains why “710,000 heat deaths” is a modeled epidemiological estimate rather than a direct tally from death certificates. Most heat deaths are certified under ICD-10 codes for cardiac arrest, respiratory failure, or other primary causes — not under code X30 (exposure to excessive natural heat). Direct ICD-10 coding massively undercounts the true burden. The Lancet Countdown uses excess mortality analysis combined with attribution modeling, producing estimates that capture deaths caused by heat even when not labeled as such. The 710,000 figure is therefore conservative: it is likely an underestimate of the true burden, not an overestimate.

Who Bears the Heat Burden

The demographic distribution of heat mortality is not uniform, and the 2026 Countdown documents the specific populations where the burden concentrates. Older adults — particularly those aged 85 and above — face disproportionate heat mortality risk due to reduced physiological capacity to thermoregulate. Outdoor workers in agriculture and construction, concentrated in lower-income countries, face both occupational exposure and limited access to cooling. Agricultural laborers in the most heat-vulnerable regions can lose as much as 8% of economic output to heat-related productivity loss in a single year.

The economic scale of heat exposure is now quantifiable in the trillions. Earlier Lancet Countdown reports drawing on 2024 data estimated that heat caused $1.09 trillion in income losses globally in a single year. The 2026 report documents that economic losses from weather-related extreme events have continued to increase, with costs of heat-related deaths among older adults alone reaching hundreds of billions of dollars annually.

Geographically, South Asia, Sub-Saharan Africa, and the Middle East face the highest per-capita heat mortality risk. Extreme humid heat across South Asia — documented by the WWA South Asia heat study in its analysis of the April 2023 heat event — is “largely driven by climate change and detrimental to vulnerable populations.” Low- and medium-income countries as a group lose a larger share of GDP to heat exposure than wealthier nations, compounding health inequality with economic vulnerability.

Drought, Food Security, and Compounding Hazards

Heat mortality is one dimension of what the 2026 report characterizes as an accelerating climate health crisis. Nearly half of all global land area was affected by at least one extreme drought month in recent years — a proportion that has grown substantially since the mid-twentieth century. Worsening hydrological extremes compound the mortality burden in ways that do not always register in heat-death statistics.

Drought degrades food security, compromises water quality, and erodes the agricultural productivity on which the health of low-income populations depends. The 2026 Countdown specifically highlights the interplay between drought, food insecurity, and heat, describing a system of compounding harms: as heat stress reduces labor capacity precisely in the seasons and sectors most exposed to drought, the economic feedback is self-reinforcing. The report characterizes this not as a series of isolated events but as a structural health emergency — the framing that underlies its formal emergency declaration demand.

What Declaring a Climate Health Emergency Would Actually Mean

The 2026 Lancet Countdown’s call for climate change to be formally recognized as a global health emergency points toward a specific institutional mechanism: a Public Health Emergency of International Concern (PHEIC) under the International Health Regulations (IHR, 2005). A PHEIC is the WHO’s highest-tier alert designation, previously applied exclusively to communicable disease emergencies — including H1N1 influenza (2009), Ebola (2014 and again in 2018), Zika (2015–2016), and COVID-19 (2020). Climate change has never received PHEIC designation.

Under IHR Article 12, a PHEIC requires the WHO Director-General’s determination that an event constitutes “a public health risk to other States through the international spread of disease” and potentially requires “a coordinated international response.” The Lancet report’s argument is that the scale of climate-attributable heat mortality already meets the functional threshold for such a response, even if the IHR’s original drafting assumed communicable pathogen spread rather than systemic atmospheric change.

A critical limitation worth noting: a PHEIC does not come with a dedicated funding mechanism. It creates legal coordination obligations for WHO member states under Article 44 and triggers WHO technical assistance provisions under Article 13, but it does not unlock automatic emergency financing. The Lancet Countdown’s call, if adopted, would require separate political decisions about financing to translate legal obligations into funded health-system responses.

The research community’s pressure for that designation has been building independently of the 2026 report. In September 2026, Prof. Matthew Chersich of Wits University co-authored a Lancet letter calling on WHO to formally declare climate a PHEIC, a pre-Lancet-Countdown escalation that the 2026 report’s findings now extend. In May 2026, a Pan-European Commission on Climate and Health chaired by former Iceland Prime Minister Katrín Jakobsdóttir and convened by WHO Europe Regional Director Dr. Hans Henri P. Kluge similarly called for WHO to formally recognize climate as a public health emergency of international concern.

“Climate change is already harming health in every region of the world, and the evidence shows that many of these impacts are accelerating,” said Diarmid Campbell-Lendrum, who heads 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. Cleaner energy, stronger health systems and early warning systems are saving lives today.”

What Progress There Is — and What COP31 Faces

The 2026 Countdown documents genuine gains alongside the mortality trend. Global investment in clean energy reached a global clean energy investment record of $2.1 trillion in 2025 — a figure that, if sustained and scaled, carries genuine implications for long-term climate health outcomes. Countries that have successfully reduced fossil fuel-related air pollution are already realizing measurable mortality benefits, with estimates suggesting that reduced coal combustion alone is preventing approximately 160,000 premature deaths annually in some modeling scenarios. The report also notes increases in national health adaptation planning and the spread of climate-informed early warning systems for extreme heat events.

But the central tension the 2026 Countdown identifies is between the pace of those gains and the pace of the underlying hazard. The atmospheric CO₂ that drove 2023’s 710,000 heat deaths is already in the air. The benefits of today’s clean energy investment arrive with a lag measured in decades; the mortality burden arrives every summer.

COP31, scheduled to open November 9 in Antalya, Turkey, is the next major opportunity to integrate health explicitly into climate mitigation commitments, adaptation finance, and loss-and-damage frameworks. WHO’s Alliance for Transformative Action on Climate and Health (ATACH) continues to operate as the institutional vehicle for health-ministry coordination at the country level, and WHO says it is taking steps to use existing instruments to respond to climate emergencies in line with the Lancet report’s recommendations.

The COP31 host country’s own climate record complicates that backdrop. Turkey announced an expansion of the Cenal Coal Power Plant in June 2026, adding 1,050 megawatts (MW) of new capacity and raising the Turkey’s Cenal coal expansion announced plant’s total installed capacity to 2,370 MW. “The COP31 presidency is coming up short,” said campaigner Duygu Kutluay. “Türkiye has no plan to fully phase out coal while the rest of Europe leaves it behind.”

The Lancet Countdown’s core finding is that the diplomatic framework operating for a decade has not reversed the health trend it was meant to address. The 36% increase in post-Paris heat mortality is not a scenario. It is a measurement. The question for COP31 is whether health will finally be treated as a first-order outcome of climate decisions, rather than a consequence that surveillance scientists document after the fact.

Frequently Asked Questions

What is the Lancet Countdown on Health and Climate Change?

The Lancet Countdown is an annual global surveillance report, established in 2015 and published each year in The Lancet medical journal, that tracks 54 indicators measuring the relationship between climate change and human health. It is produced by 146 researchers from 71 collaborating institutions across more than 30 countries in strategic collaboration with the World Health Organization. It was founded specifically to measure whether the Paris Agreement — adopted in 2015 and in force since November 2016 — was delivering the health benefits its climate goals implied.

How do researchers attribute 70% of heat deaths to human-caused climate change?

The attribution uses a statistical method called Fraction Attributable Risk (FAR), which compares what actually happened to a counterfactual scenario modeled without human greenhouse gas emissions. Researchers run climate models with and without anthropogenic emissions and calculate what fraction of observed heat mortality would not have occurred in the emissions-free scenario. That fraction — more than 70% for 2023’s global heat toll — represents deaths that required human-caused warming to happen. The same methodology, applied at the scale of individual weather events, has been used by groups like World Weather Attribution to quantify climate change’s role in specific heatwaves within days of their occurrence.

What would declaring climate change a PHEIC actually do?

A PHEIC — a Public Health Emergency of International Concern under the International Health Regulations (2005) — is the WHO’s highest-tier alert. It creates legal coordination obligations for member states and triggers WHO technical assistance provisions, but it does not automatically unlock dedicated funding. Every prior PHEIC has addressed communicable disease spread (H1N1, Ebola, Zika, COVID-19). Extending the mechanism to a systemic, slow-onset hazard like climate change would require either a creative application of existing IHR criteria or a formal IHR amendment — a significant institutional step that would require member-state agreement, including from countries with major fossil fuel industries.

What can I do with this information ahead of COP31?

COP31 opens November 9, 2026 in Antalya, Turkey. National governments send their delegations; climate finance, adaptation commitments, and loss-and-damage frameworks are all on the negotiating agenda. Individual readers can contact elected representatives to ask how their country is integrating health into its COP31 positions; monitor whether their country’s NDC (Nationally Determined Contribution) treats reduced heat mortality as a target rather than a hoped-for side effect; and follow whether ATACH’s network of health ministries successfully secures dedicated adaptation financing for climate-resilient health systems in the final COP31 text.