More than 450,000 dead by February? These are the potential devastations that the intense heat linked to this year’s “super El Niño” could cause, according to a new report from the Climate Impact Lab (CIL), published Wednesday September 23.
El Niño is a natural climatic phenomenon, but global warming could make it worse.
“We have long been able to predict the impact of temperatures on crops, and now we can predict their impact on the worst-case scenario: death,” explains Michael Greenstone, co-founder of the Climate Impact Lab. “As a result, we estimate that 451,000 deaths could occur in the coming months due to El Niño.”
The authors of the report specify that they started from a statistical relationship already established by the CIL between temperature and excess mortality, taking into account the local climate, vulnerability and capacity for adaptation.
This relationship is applied to 24,378 regions around the world, then crossed with data from the SEAS5 seasonal forecast system relating to temperature anomalies. Uncertainty from both seasonal weather and the temperature-mortality relationship is incorporated into the results.
“This number is so high that it can be chilling: these are parents and children, grandparents and neighbors, people who go to work, take care of their families and live their lives.”
Michael Greenstone, co-founder of CIL, professor emeritus of economics at the University of Chicago
The figure put forward by the CIL adding to the consequences of droughts, forest fires and floods expected due to rising temperatures and changes in precipitation patterns, this El Niño episode – which also recorded a record temperature on September 21 several months before its expected peak – could well become the most intense ever recorded.
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More worryingly, the report shows that the episode, which began in June, is expected to raise global temperatures around 1.2°C above normal in the coming months, temporarily exposing much of the world to heat levels that climate change is expected to make usual within around 20 years.
Beyond the human toll announced, researchers therefore see in this “super El Niño” a warning: today’s exceptional heat provides a glimpse of what could become ordinary in a few decades. And above all, some of the expected deaths can still be avoided.
“A postcard from the future”
“El Niño is, in fact, propelling us into the future.” The formula appears at the opening of the report and summarizes the structuring idea of the document according to which the current episode constitutes an anticipated exposure to thermal conditions expected to become ordinary under the effect of climate change.
“It’s more than a hot summer : it’s a postcard from the future”
Climate Impact Lab report, September 2026
Over the six months from September 2026 to February 2027, the CIL estimates the number of additional heat-related deaths worldwide at 239,000 (compared to the 1996-2025 average, and with an uncertainty margin of plus or minus 11,000).
The authors emphasize that this toll is expected to increase further, with El Niño expected to persist until spring 2027 and above-normal temperatures possibly persisting until June or even July.
The largest increases in mortality would be concentrated in the global South, with particularly large outbreaks in the Sahel, South and Southeast Asia, Central Africa and parts of South America.
The Sahel would pay the heaviest price, with 66,800 additional heat-related deaths expected between September and February, including 31,400 in Nigeria, 17,500 in Sudan, 10,000 in Niger and 8,000 in Chad.
Indonesia could have 19,300 additional deaths, India 15,800 and Brazil 13,300. In Southeast Asia, the Philippines, Vietnam, Thailand and Cambodia would total 19,400 additional deaths.
Estimated additional number of heat-related deaths between September 2026 and February 2027 compared to the period 1996-2025. © Climate Impact Lab (CIL) 2026 Report
However, tropical countries would not be the only ones affected. In the United States, some 3,500 additional heat-related deaths are expected, which would place the country among the 20 most affected in the world, according to CIL projections reported by the Guardian.
According to Michael Greenstone, the report allows decision-makers “to precisely identify the emergency measures to be taken now to save tens of thousands of lives in the months to come.”
Indeed, deaths will not all occur simultaneously. Some of the most affected countries are expected to experience a significant portion of their excess mortality between December 2026 and February 2027, which, according to the authors, leaves time to intervene.
Thus, the CIL considers that targeted interventions could still make it possible to reduce the number of deaths by several tens of thousands. The report specifically seeks to identify geographic areas and periods where immediate action could have the most impact.
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Tens of thousands of deaths could still be avoided
Among the actions identified by the “CIL Adaptation Inventory” (a database listing adaptation interventions that have already demonstrated their ability to save lives and improve human well-being, editor’s note) include heat alerts, health actions for vulnerable populations, cooling centers, hydration points, protection for workers and strengthening the capacities of health systems.
The report also mentions advance funding, heat action plans with monitoring of related symptoms, home visits, improved access to water, improved temperature forecasts and wider access to cooling technologies.
However, as a number of these measures have only been evaluated in specific geographic areas, experts call for increasing knowledge about the effectiveness of different strategies across regions, climates and health systems, and then investing in preparedness and planning.
It now remains to determine which measures are the most effective depending on the territories: a crucial issue, according to the CIL, to prepare populations for heat expected to become more and more frequent.
This is all the more urgent as heat-related mortality is already increasing sharply as a result of global warming. According to the latest Lancet Countdown global report, published in 2025, some 546,000 people now die each year from extreme heat, 23% more than in the 1990s.
