Heat was linked to an estimated 710,000 deaths worldwide in 2023, a single-year record. The 2026 report puts about 71% of that toll down to human-caused climate change, and says the number exceeds annual deaths from malaria or HIV.

The report was published on Oct. 27-28 by 146 researchers from more than 100 institutions in over 30 countries, led by University College London and developed in collaboration with the World Health Organization (WHO). Its headline message: climate change should be treated as a global health emergency.

The numbers behind the headline

According to WHO's summary of the report, annual average heat-related deaths rose by nearly 36% in the years since the Paris Agreement compared with the decade before it. The Lancet Countdown's own findings say many health harms grew faster in 2016 to 2025 than in 2006 to 2015.

The report also attributes heat deaths to climate change for the first time as a tracked indicator. Averaged over 2016 to 2023, heat was linked to more than 540,000 estimated deaths per year, and the researchers attribute 68% of them to climate change, ABC News reported. Across the whole period, that is nearly 3 million deaths.

These are modelled estimates, not counted death certificates. Most heat deaths never appear in records as heat deaths. They appear as heart failure, kidney injury or a stroke on a hot afternoon. A Dawn editorial in Pakistan made the same point this week: a patient arriving with dehydration or breathing trouble may be suffering from extreme weather without the link ever entering the medical record. The Lancet figure is best read as the size of a gap in public health data as much as a death toll.

Fossil fuels in the lungs

Heat is only one channel. The authors found that fossil fuels still supply more than 80% of global energy, and that the resulting air pollution is responsible for about 2.7 million deaths a year, according to ABC's reading of the report.

This is the part of the story that gets the least attention, and it matters for policy. The report notes that many countries that cut fossil-fuel air pollution are now protecting thousands of people from premature death each year, and WHO says global clean energy investment hit a record $2.1 trillion in 2025.

"Climate action is a health intervention," said Dr Diarmid Campbell-Lendrum, head of WHO's climate change, air quality and energy and health unit. Framing climate action as health policy speaks to finance and health ministries as well as environment ministries.

A health-first demand

The authors call for climate change to be formally recognised and addressed as a global health emergency, and for health to be built into decisions on emissions cuts, adaptation and climate finance. Marina Romanello, the project's executive director, said the numbers point to a clear emergency, according to ABC News.

WHO is already acting like it. Since September, the agency says, it has been responding to the expected health impacts of the ongoing El Niño through a graded emergency response and a Global Incident Management Team, supporting the countries most at risk. WHO also notes that a public health emergency of international concern under the International Health Regulations can include events driven by climate change.

That does not mean one is coming. WHO defines a PHEIC as an event that poses a risk to other states through international spread of disease, and heat exposure is not an obvious fit for that definition. The practical value of the phrase "health emergency" is political: it moves climate off the environment ministry's desk.

What to watch at COP31

Governments meet for COP31 in November, and WHO has scheduled a health pavilion there from Nov. 9 to 20. That is the first test of whether health arguments can change climate negotiations, rather than decorate them.

The weak point is the same one that surfaced in this year's biodiversity talks, where COP17 delegates deadlocked over who pays and pledges sat far below the target. The Lancet Countdown gives ministers a number they cannot easily dismiss, 710,000 deaths, but a number is not a budget.

My read is that the most useful thing in this report is not the death toll. It is the case that a country can justify clean-energy spending to its own health ministry on its own terms, without waiting for other countries to move first.