El Niño could cause 451,000 excess heat deaths, offering glimpse of climate future

Peruvian fishermen named it centuries ago—El Niño, the little boy, or Christ Child—after noticing warm Pacific waters appearing around Christmas that scattered the fish they relied on. What those fishermen saw in their local waters can reshape weather patterns thousands of kilometers away, bringing scorching heat and drought to some places while dumping torrential rain on others. Today, researchers estimate that the unusually high temperatures tied to the current El Niño event could cause around 451,000 excess deaths worldwide between June 2026 and February 2027.

The mechanism is straightforward in its brutality. Normally, trade winds push warm surface water westward across the Pacific toward Asia and Australia, allowing colder water to rise near South America. During El Niño, which arrives unpredictably every two to seven years, those winds weaken. Less cold water rises to replace the warm surface layer, leaving much of the Pacific abnormally heated. That warmer water warms the air above it and fuels rainfall over the central and eastern Pacific. The rising air spreads high into the atmosphere, sending waves that ripple outward and disrupt weather worldwide. Climate researcher Fred Kucharski described it simply: throwing a stone into a lake. The initial disturbance is local, but the energy spreads everywhere through wave propagation. The effects can cross the tropics in a week and reach higher latitudes in about two. Where those waves travel determines whether a region becomes hotter, cooler, wetter, or drier.

The current El Niño developed in June and has strengthened rapidly since, now on course to become exceptionally strong—sometimes called a "super" El Niño. Land temperatures over the coming months are forecast to run about 1.2 degrees Celsius (2.1 Fahrenheit) above normal. Tamma Carleton, head of research at the University of Chicago's Climate Impact Lab, framed this starkly: "For the average person, that's roughly the warming climate change is projected to bring about 20 years from now, arriving all at once." The 451,000 figure covers only the first nine months of El Niño, as far as current seasonal forecasts extend. The event is expected to continue into Northern Hemisphere spring, and its effect on global temperatures could persist longer. Carleton said they expect the final number to be meaningfully higher than what they are currently reporting.

Extreme heat kills through direct physiological assault. It strains the heart and kidneys, makes it harder for the body to maintain a safe temperature, and worsens cardiovascular, respiratory, and other illnesses. Often, the underlying condition is recorded as the cause of death rather than the heat that triggered or accelerated it. Most heat deaths never appear in official statistics as heat deaths. El Niño also alters rainfall patterns, contributing to drought in some regions and heavy rain and flooding in others. Floods kill directly, contaminate drinking water, and spread disease. Drought damages harvests and causes water and food shortages. Deaths from these indirect effects are not included in the 451,000 projection, meaning the true toll could be substantially higher.

The Climate Impact Lab expects some of the largest increases in deaths in the Sahel, South Asia, 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. Carleton noted a stark geographic reality: "Heat headlines usually focus on Europe and North America. 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."

A critical question shadows the estimate: Are these lives being significantly shortened, or is the heat merely bringing forward deaths that would have occurred days or weeks later? Some people who die during extreme heat are already frail. 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 independently 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."

Scientists have long estimated the death toll from extreme temperatures after the fact, counting bodies once the event had passed. Better seasonal forecasting is now allowing researchers to look ahead instead. To produce the estimate, researchers combined earlier work showing how death rates change during hot weather in different parts of the world with seasonal forecasts showing how hot each place is expected to become. Putting the two together lets them estimate the human cost while there is still time to act. 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 routine. "This El Niño gives us a look at future weather in the 2040s," she said. "These temperatures will become normal in 20 years, giving us time and reason to begin investing in adaptive capacity now." The current event is a postcard from a future that is already being written.