Summary
A Nature Medicine study using global temperature and mortality data estimates that very strong El Niño years are associated with more heat-related deaths and fewer cold-related deaths worldwide. The estimated increase in heat mortality was concentrated in low- and medium-HDI countries.
A peer-reviewed study in Nature Medicine estimates that very strong El Niño years are associated with a rise in global heat-related mortality and a smaller fall in cold-related mortality. The researchers integrated global temperature and mortality databases with epidemiological models to assess how mortality linked to temperature varied with El Niño-Southern Oscillation (ENSO).
ENSO is a climate pattern involving interactions between the ocean and atmosphere that can influence temperatures across the world. The study’s findings describe population-level associations estimated by models, rather than evidence that ENSO directly caused individual deaths.
Estimated changes in heat- and cold-related mortality
For very strong El Niño years, the analysis estimated a 28.87% increase in global heat-related mortality, corresponding to 107,035 additional annual deaths (95% eCI: 27,336 to 176,312). It also estimated a 3.70% decrease in cold-related mortality, or 112,681 fewer annual deaths (95% eCI: −207,619 to −22,203).
The researchers report these as annual mortality estimates associated with very strong El Niño conditions. The opposing heat and cold estimates show why temperature-related health burdens need to be considered together: warmer conditions can raise heat-related mortality while reducing deaths associated with cold.
Burden was concentrated in lower-HDI countries
The estimated increase in heat-related mortality was concentrated in countries with low and medium human development index (HDI), which together accounted for 67.65% of the global increase. Medium-HDI countries had the largest estimated rise: 61,863 additional annual deaths (95% eCI: 19,939 to 105,888).
The study’s point estimates for the combined heat- and cold-related burden suggest a shift from high-HDI countries toward lower-HDI countries. The authors say that, as temperatures continue to warm, future El Niño events could pose additional public-health challenges and highlight the value of climate-informed preparedness.
The figures are epidemiological model estimates based on global temperature and mortality data. They quantify associations across populations; the reported results do not by themselves establish a direct causal effect of ENSO on any individual death.