As an unusually intense El Niño event builds in the tropical Pacific Ocean, a groundbreaking new analysis from the University of Chicago’s Climate Impact Lab has delivered a stark warning: the natural climate phenomenon could lead to approximately 451,000 additional heat-related deaths across the globe over the coming six months. Researchers emphasize that this figure is a model-based risk assessment, not a precise prediction of exact fatalities, calculating excess mortality against baseline temperature averages for a typical year.
The analysis currently focuses on the period from September 2026 through February 2027, but the team warns that the impacts of record-breaking heat may linger long after this window, particularly as spring and summer arrive in the Northern Hemisphere. The warning comes as leading meteorological bodies around the world confirm that El Niño is rapidly gaining strength.
Early this month, the World Meteorological Organization (WMO) stated there is a near-certain chance the event will persist through February 2027, and is on track to intensify into a rare “strong event” that will peak by the end of 2026. The U.S. National Oceanic and Atmospheric Administration (NOAA) echoes this assessment, reporting that sea surface temperatures in parts of the equatorial Pacific are already more than 3 degrees Celsius above the long-term average. NOAA estimates the probability of this event ranking among the most intense El Niños on record reaching 75% for the October to December 2026 period.
El Niño reshapes global atmospheric circulation patterns, leading to drastically different impacts across regions: some face deadly extreme heat and crippling drought, while others are hit by catastrophic heavy rainfall and flooding. For the upcoming event, Climate Impact Lab projects global average land temperatures will sit 1.2 degrees Celsius above non-El Niño baselines, with the number of extreme heat days rising by 44% compared to average years.
The worst impacts are projected to fall disproportionately on low-income, warmer regions across Africa, Asia, and South America. The Sahel region is expected to see roughly 66,800 excess heat-related deaths, with Nigeria hit hardest at approximately 31,400 additional fatalities, followed by Sudan with 17,500. Other heavily impacted nations include Indonesia (19,300), India (15,800), and Brazil (13,300).
Michael Greenstone, co-founder of the Climate Impact Lab and a co-author of the study, explained that vulnerability extends beyond raw temperature increases. “If you already live in a warm place, those extra couple of degrees are far more dangerous,” he said. Additional factors shaping mortality risk include population size, population exposure to unregulated high temperatures, access to healthcare, electricity and cooling, and governmental capacity to implement adaptive measures. Lower-resource nations face compounded risk, as extreme heat often overlaps with pre-existing crises in food security, energy access, and public health infrastructure.
Notably, the 451,000 figure only accounts for excess heat-related mortality. The total health toll of the event could be far higher, as strong El Niños also trigger droughts, wildfires, extreme flooding, and disruptions to agricultural production that further strain food security across vulnerable parts of Asia and Africa. Earlier this month, the World Health Organization (WHO) warned that the 2026 El Niño will bring a wide range of interconnected health risks, urging nations to prioritize preparation for vulnerable communities and already overburdened health systems. The WHO notes that heat is already one of the leading causes of weather-related mortality globally, with an average of 489,000 heat-related deaths recorded annually between 2000 and 2019.
While El Niño itself is a natural periodic cycle of ocean and atmospheric conditions in the tropical Pacific, not a direct product of anthropogenic climate change, it is unfolding on a planet already warmed significantly by human-caused greenhouse gas emissions. This means the baseline global temperature is already higher, amplifying the extreme heat impacts of even a natural El Niño event. The WHO confirms that combining El Niño with long-term climate change-driven warming significantly increases the probability of extreme heat events across most regions. Researchers stress they are measuring excess mortality against a baseline average year, rather than attributing every extreme temperature or death directly to El Niño.
The 451,000 estimate carries important caveats: it is not an observed fact or a guaranteed outcome. Researchers produced the figure by combining historical temperature-mortality relationships across thousands of global regions with projected temperature trends for the coming months, leaving exact regional outcomes uncertain. External climate factors can either amplify or dampen El Niño’s impacts, and heat sensitivity varies across populations. The WMO adds that El Niño strength alone does not determine local weather, with conditions in the Indian and Atlantic Oceans also able to reshape regional impacts. As such, the study is framed primarily as a warning about the scale of potential risk, not an exact prediction of fatalities.
Despite the grim projection, researchers note that there is still time for governments to act to reduce harm. Targeted preparedness measures including early extreme heat warnings, public cooling centers, improved workplace protections for outdoor laborers, and expanded healthcare capacity during heat events can cut mortality significantly. The WHO shares this conclusion, noting that most heat-related health impacts are predictable and preventable with timely, coordinated action. With El Niño projected to continue strengthening through the end of 2026 and persist at minimum through February 2027, the coming months are seen as a critical window for preparation to avoid preventable deaths.