LATIN AMERICA · CLIMATE AND HEALTH
Hot years in the tropics get deadlier when El Niño, a periodic warming of the tropical Pacific Ocean, shifts rain and heat around the world. A study in Nature Medicine, a leading medical journal, links very strong El Niño years to about 107,000 extra heat deaths a year, with South America hit hardest in percentage terms.
The study looks at past years, so it does not forecast deaths in the 2026-2027 El Niño. Mexico’s weather service forecast in July that a very strong El Niño was likely in 2026-2027, and Peru has budgeted money to prepare.
Key Facts
- Heat deaths Very strong El Niño years add 107,035 heat deaths a year worldwide, compared with neutral years.
- Cold deaths 112,681 fewer cold-related deaths a year, so the two effects largely offset globally.
- South America Heat deaths rise 76.13% in very strong El Niño years, the largest of the regions reported.
- Inequality Countries with low and medium UN human development scores hold 42.16% of people but 67.65% of added heat deaths.
- Limit Built on past data, so it cannot directly predict deaths in the 2026-2027 El Niño.
The study counts past heat deaths in very strong El Niño years and does not forecast the current El Niño, but it shows where the risk is greatest.
In Plain English
El Niño is a periodic warming of the tropical Pacific Ocean that shifts rain and heat around the world. The researchers compared very strong El Niño years with neutral years, which serve as the baseline.
The Human Development Index (HDI) is a UN ranking of health, education and income. Countries with low and medium scores are grouped together in the study.
What the Study Found
The research was led by ISGlobal, the Barcelona Institute for Global Health, a research centre in Spain. ISGlobal released its summary on Tuesday, 10 November 2026.
Natalia Shartova is the first author, and Joan Ballester Claramunt coordinated the work. The team covered 1980 to 2023, including the very strong episodes of 1982-83, 1997-98 and 2015-16.
Compared with neutral years, very strong El Niño years are linked to 107,035 additional heat-related deaths a year worldwide. Neutral years, without El Niño or its cooler counterpart, serve as the baseline.
The same years bring 112,681 fewer cold-related deaths a year. The authors say the two effects largely offset each other globally.
That does not make El Niño harmless. Shartova said: “The fact that these two changes largely offset each other globally does not mean that El Niño is beneficial to health.”
The data came from mortality records for 1,667 regions in 125 countries. Statistical methods extended them to 3,331 regions in 189 countries, covering more than 8 billion people.
Why South America Stands Out
Annual heat deaths in very strong El Niño years rise by 76.13% in South America, the largest of the regions reported. Small island developing states, meaning small island countries, follow at 65.93%.
Sub-Saharan Africa sees a rise of 54.02%, and South and South-East Asia 43.11%. These are rises in each region’s own annual heat deaths, not shares of the global total.
Countries with low and medium HDI scores hold 42.16% of the world’s population but account for 67.65% of the estimated increase in heat deaths. The medium-HDI group has the largest absolute increase, 61,863 additional deaths a year, or 58% of the global rise.
Our Latin America news hub follows how governments in the region respond. The study itself looks only at past deaths, not at government plans.
What It Means for You
Travellers and retirees heading to South America or small island states should note that the study finds among the largest percentage rises there. The figures describe whole populations, not the risk to any one visitor.
Ballester Claramunt said the findings identify the regions and seasons most affected by El Niño. He added that this can show where preparedness matters most.
Preparation is under way in Peru, which has budgeted money, and the study may help governments decide where to focus. Whether such plans will work is not yet known.
What Is Not Known
Nobody can yet say how many deaths this El Niño will cause. The study is built on past data and cannot be used directly to predict deaths in the ongoing 2026-2027 episode.
Mortality records were unavailable for about one third of the countries analysed, mostly poorer ones. Estimates for most low-HDI countries and much of sub-Saharan Africa rely on models built with data from other regions, so they must be read with caution.
Frequently Asked Questions
What is El Niño?
El Niño is a periodic warming of the tropical Pacific Ocean that shifts rain and heat around the world. Very strong episodes in the study include 1982-83, 1997-98 and 2015-16.
Does this mean El Niño is deadly worldwide?
The two effects largely offset each other, but the authors stress this does not make El Niño beneficial to health. Very strong years bring 107,035 more heat deaths but 112,681 fewer cold deaths a year.
Which regions are hit hardest?
South America sees the largest percentage rise of the regions reported, at 76.13%, followed by small island developing states at 65.93%. Sub-Saharan Africa rises 54.02% and South and South-East Asia 43.11%.
Can the study predict deaths in the current El Niño?
No, the study uses past data from 1980 to 2023. It cannot be used directly to predict deaths in the ongoing 2026-2027 El Niño.
Sources: Nature Medicine (nature.com/nm, DOI 10.1038/s41591-026-04793-w); ISGlobal press release of 10 November 2026 (isglobal.org).
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