A powerful El Nino event now affecting the planet could lead to an estimated 451,000 excess deaths from extreme heat, according to a new report from the Climate Impact Lab (CIL), a research initiative run by the University of Chicago’s Energy Policy Institute.
The estimate covers the full period during which the warming effects of the El Nino are expected to be felt. Researchers say about 239,000 of those deaths could occur between September 2026 and February 2027 alone, based on current seasonal forecasts. The researchers estimate that the remaining deaths could occur as the effects of the event continue into the middle of 2027.
The scale of the projection is remarkable. The report says the estimated deaths in the next six months could be about 65 times the number of people believed to have died or gone missing in the recent Nepal flash flood, which claimed about 6,800 lives.
A hotter world arriving sooner
The current El Nino began in June 2026 and is expected to continue through the Northern Hemisphere spring. Researchers project that global land temperatures could be about 1.2°C, or 2.1°F, above normal in the coming months. The researchers say these conditions resemble what climate models had projected could become common only about two decades from now.
The forecast also points to a sharp rise in extreme heat. The report estimates that the period could bring 44% more extremely hot days than a typical year. To estimate the possible death toll, researchers used seasonal forecasts from the European Centre for Medium-Range Weather Forecasts and a 51-member forecast ensemble. They studied the relationship between temperature and mortality across 24,378 regions around the world.
The projections were compared with temperature and mortality patterns recorded between 1996 and 2025. This region-by-region approach allowed researchers to estimate not only the overall number of additional deaths, but also where the risks could be highest and when they could occur.
Developing countries face the biggest risks
The largest increases in heat-related deaths are expected in parts of the Global South, where high temperatures often overlap with greater exposure to outdoor work, limited access to cooling and weaker health infrastructure. The Sahel is projected to record about 66,800 additional heat-related deaths between September 2026 and February 2027.
Nigeria alone could account for nearly half of that number, with an estimated 31,400 additional deaths. Sudan could see about 17,500, while Niger and Chad could record about 10,000 and 8,000 respectively.
Southeast Asia is also expected to face a significant increase in heat-related mortality. The Philippines, Vietnam, Thailand and Cambodia together could see about 19,400 additional deaths. Indonesia alone is projected to record another 19,300. India and Brazil are also among the countries facing a substantial increase, with an estimated 15,800 and 13,300 additional deaths respectively.
The 10 countries with the highest projected additional deaths are Nigeria, Indonesia, Sudan, India, Brazil, the Democratic Republic of the Congo, Niger, Chad, the Philippines and South Sudan. The Democratic Republic of the Congo is projected to see about 10,000 additional deaths during the six-month period.
The timing of deaths could vary
The effects of extreme heat will not be spread evenly across the forecast period. In some countries, the largest increase in deaths is expected later in the six-month window, between December 2026 and February 2027.
Nigeria could see about 15,400 additional deaths during these three months, while Indonesia could record about 10,400. Brazil and India are also expected to experience their highest projected mortality during this period, with about 8,000 and 7,400 additional deaths respectively.
The timing is important because many of these deaths have not yet occurred. This means governments and humanitarian organisations still have time to prepare for the periods when heat exposure is expected to be highest. Measures such as early warnings, access to drinking water and cooling spaces, health outreach and protections for outdoor workers could help reduce the impact.
India could face further risks in 2027
The heat risk is not expected to end when the current six-month forecast period closes. Researchers expect heat-related deaths to continue rising into the middle of 2027 in parts of the Northern Hemisphere, including India and Pakistan, as these countries move into their hotter summer months.
The projected increase is particularly important because extreme heat can affect large populations at the same time. People who work outdoors, older adults, people with existing health vulnerabilities and those without access to cooling can face greater exposure. The researchers say more localised forecasts could help governments identify the areas where intervention is needed most.
A chance to act before the heat peaks
One of the main aims of the report is to move the focus from counting deaths after an extreme heat event to preventing them before they happen. The Climate Impact Lab plans to continue updating its forecasts and has developed an interactive tool that can help track changing mortality risks.
The researchers say such information could help governments, humanitarian organisations and other agencies decide where emergency funding and other resources should be sent. The report also points to the Climate Impact Lab’s Adaptation Inventory, which brings together evidence on measures that can help communities cope with extreme heat. These include heat warning systems, cooling centres, hydration stations, health outreach to vulnerable people, protections for workers exposed to high temperatures and greater capacity in health systems.
Lessons from extreme heat
The report describes the current El Nino as “a postcard from the future”. The idea is that the extreme temperatures being experienced now may give a glimpse of conditions that could become more common as the planet warms.
El Nino itself is a natural climate pattern, but its effects are now unfolding against a warmer global climate. This means an event that would once have produced a certain level of heat can now push temperatures to even more dangerous levels.
The researchers argue that climate change also gives governments an opportunity that a sudden El Niño event does not: time to prepare. Building heat warning systems, expanding access to water and cooling, improving temperature forecasts and strengthening local health services can help communities respond before temperatures reach dangerous levels.
Preparing for the next heat event
Some interventions are already showing promise. These include early financing before a heat event, heat warning systems linked to action plans, health workers making home visits, improved access to water, monitoring of heat-related symptoms and wider access to cooling technologies. However, the researchers say there is still a major gap in evidence. Many heat interventions have been tested only in a limited number of regions, making it difficult to know how well they will work in different climates, communities and health systems.