Peruvian fishermen gave El Nino its name — "the little boy," or Christ Child — after noticing unusually warm Pacific waters around Christmas that caused the fish they depended on to suddenly become scarce.
But what those fishermen observed locally can have consequences thousands of kilometers away. El Nino can shift temperature and rainfall patterns around the world, bringing extreme heat and drought to some regions and heavy rain and flooding to others.
Researchers now estimate that the unusually high temperatures linked to the current El Nino could cause around 451,000 excess deaths worldwide from June 2026 to February 2027.
The event is a "postcard from the future," Tamma Carleton, head of research at the University of Chicago's Climate Impact Lab, told DW. Land temperatures over the coming months are forecast to run about 1.2 degrees C (2.1 F) above normal.
"For the average person, that's roughly the warming climate change is projected to bring about 20 years from now, arriving all at once," Carleton said.
How does El Nino affect weather worldwide?
Normally, winds blowing west across the Pacific push warm surface water towards Asia and Australia, allowing colder water to rise near South America. During El Nino, which occurs erratically every two to seven years, those winds weaken. Less cold water then rises, and much more of the Pacific stays unusually warm.
The warmer water heats the air above it and fuels rainfall over the central and eastern Pacific. The rising air spreads high in the atmosphere, sending waves that disrupt weather worldwide.
"It is like throwing a stone into a lake," climate researcher Fred Kucharski told DW. "Initially the surface perturbation is local, but then the energy spreads all over the lake through wave propagation."
Kucharski said the effects can cross the tropics within one week and reach higher latitudes in about two. Where the waves travel determines whether a region becomes hotter, cooler, wetter or drier.
The current El Nino developed in June and has strengthened rapidly since. It is now on course to become an exceptionally strong — sometimes called "super" — El Nino.
The Climate Impact Lab says its estimate covers only the first nine months of El Nino, as far as the current seasonal forecasts allow. The event is expected to continue into Northern Hemisphere spring, and its effect on global temperatures could last longer.
"We expect the final number to be meaningfully higher than what we are currently reporting here," Carleton said.
Why can El Nino be so deadly?
The estimate of 451,000 excess deaths covers deaths linked to the direct health effects of unusually high temperatures associated with El Nino.
Extreme heat strains the heart and kidneys, makes it harder for the body to maintain a safe temperature and can worsen cardiovascular, respiratory and other illnesses. As a result, the underlying condition is often recorded as the cause of death rather than the heat that aggravated it.
"Most heat deaths never show up in official statistics as heat deaths," Carleton said.
El Nino can also alter rainfall, contributing to drought in some regions and heavy rain and flooding in others.
Floods can kill, contaminate drinking water and spread disease. Drought can damage harvests and cause water and food shortages.
Deaths from these other indirect effects are not included in the 451,000 projection.
Where will the toll be greatest?
The Climate Impact Lab expects some of the largest increases in deaths in the Sahel, South and Southeast Asia and parts of Latin America. The highest numbers of fatalities are predicted for Nigeria, Sudan, Niger, Chad, India, Indonesia and Brazil.
Many are projected to occur between December and February, meaning much of the expected toll still lies ahead.
"Heat headlines usually focus on Europe and North America," Carleton said. "This event's toll is overwhelmingly in lower-income, already-hot countries, where people have the fewest ways to adapt and where these deaths are least likely to be counted."
Are these lives being significantly shortened?
Some people who die during extreme heat are already frail. This raises an important question: Is the heat cutting their lives substantially short, or merely bringing forward deaths that would have occurred days or weeks later — an effect known as mortality displacement?
The underlying research uses annual rather than daily death rates, which largely filters out deaths brought forward by only days or weeks.
Ben Armstrong, an emeritus professor at the London School of Hygiene and Tropical Medicine, said he could not verify the 451,000 figure. But because the estimate is based on annual mortality data, it largely excludes deaths brought forward by only days or weeks. If the figure is correct, he said, most of those counted "would have lived at least six months longer."
Why predict deaths before they happen?
Scientists have long estimated the death toll from extreme temperatures retrospectively. Better seasonal forecasting is increasingly allowing researchers to look ahead instead.
To produce the estimate, researchers used earlier work showing how death rates change during hot weather in different parts of the world. They combined it with seasonal forecasts showing how hot each place is expected to become.
"Putting the two together lets us estimate the human cost of this event while there's still time to do something about it, rather than counting the deaths after the fact," Carleton said.
Heat warnings, cooling centers and hydration stations, home visits to vulnerable people, protections for outdoor workers and additional health care capacity could all reduce mortality.
The researchers believe targeted interventions could save tens of thousands of lives.
For Carleton, the forecast is a warning to prepare now for the heat that climate change could make commonplace.
"This El Nino gives us a look at future weather in the 2040s," Carleton said. "These temperatures will become normal in 20 years, giving us time and reason to begin investing in adaptive capacity now."
Edited: Carla Bleiker
