Researchers at the Barcelona Institute for Global Health estimate that the strongest El Niño episodes since 1980 added 107,035 heat-related deaths per year worldwide while removing 112,681 cold-related deaths. The paper appeared in Nature Medicine with an article date of Nov. 4, and the institute pushed out its press release on Nov. 9. It arrives while the tropical Pacific is already deep into another warm phase.
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A 3,331-region model built on 1,667 regions of records
The team used climate and mortality data from 1980 through 2023, a span that includes the 1982-83, 1997-98 and 2015-16 episodes, and compared very strong El Niño years with neutral ones. Actual death records existed for 1,667 regions in 125 countries. Statistical models then stretched those relationships to 3,331 regions in 189 countries, covering more than 8 billion people.
The work was led from ISGlobal, with N. Shartova as first author and J. Ballester as study coordinator, and the findings were circulated through a press release on EurekAlert and the journal itself under DOI 10.1038/s41591-026-04793-w. The two central estimates are associations between ocean conditions and temperature-related mortality, estimated against what neutral years would have produced, rather than a count of certificates marked El Niño.
That design matters for how far the numbers can travel. Observed mortality in 1,667 regions anchors the estimates, and the remaining regions inherit relationships learned from the places that do report. The 1980-2023 window contains three named very strong episodes, 1982-83, 1997-98 and 2015-16, so the signal is read across several decades in which populations, health systems and the background climate all changed.
South America, island states and sub-Saharan Africa take the steepest increases
Heat-related mortality rose most in South America, by 76.13%, followed by Small Island Developing States at 65.93%, sub-Saharan Africa at 54.02% and South and South-East Asia at 43.11%. Tropical regions showed the largest relative increases even where the temperature change itself was modest, because the populations there have little room between ordinary heat and dangerous heat.
Wealth sorts the toll as sharply as latitude does. Countries with low or medium scores on the Human Development Index hold 42.16% of the world’s population but account for 67.65% of the estimated heat-death increase. The medium group alone showed the biggest absolute jump, at 61,863 additional deaths per year, which is 58% of the global increase.
Reading the totals alongside the regional percentages shows why the authors frame the work around preparedness rather than a single global tally. A percentage increase in a tropical region with modest seasonal swings can still mean a large jump in risk for the people who live there, which is the pattern the regional figures above describe.
A near-cancellation in the totals that says little about who is safe
Because 112,681 fewer cold deaths nearly matches 107,035 extra heat deaths, a reader could be tempted to call El Niño a wash. Shartova rejects that reading directly: in the study’s words, the fact that the two changes largely offset each other globally does not mean El Niño is beneficial to health. The figures are sums across the planet, and a death avoided in one place does not return a life lost somewhere else.
Data gaps weigh on the numbers too. Mortality records were missing for about one-third of the countries analysed, mostly under-resourced ones, so estimates for many low-development countries and much of sub-Saharan Africa come from models trained on other regions. The authors say those results should be read cautiously. They also note that El Niño reaches beyond temperature into floods and droughts, which this paper does not count.
The 2026-27 episode and the limits on forecasting deaths
NOAA’s Climate Prediction Center issued an El Niño advisory in its Oct. 8 diagnostic discussion, reporting a Nino-3.4 anomaly of +2.1 degrees C and saying a strong-to-very-strong event is likely through January-March 2027. Forecasters put the chance of a historic reading, a three-month index of +2.5 degrees C or higher, at 83% for October-December. For November, NOAA’s national summary leans warm for most of the Lower 48.
The Pacific conditions behind that outlook are extreme by any measure. The same discussion reports sea surface temperature anomalies above +4.0 degrees C in parts of the eastern equatorial Pacific, a Nino-1+2 anomaly of +3.9 degrees C, and a deeper-than-average thermocline. It puts the odds of a historic event at 54% for September-November and 70% for November-January, so the heat-death pattern the study measured is not a distant scenario for health planners in the regions it flags.
The ISGlobal authors are explicit that their retrospective associations cannot be used directly to predict mortality during the ongoing 2026-2027 episode. Ballester says the value lies in identifying which regions and seasons are hit hardest, so that health agencies can prepare region-specific warnings and target at-risk groups. The next Climate Prediction Center update is scheduled for Nov. 12, and it will show whether the current event keeps climbing toward the very strong class the study examined.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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