El Niño heat could cause 451 000 additional deaths worldwide by February 2027 as Pacific temperatures reach record levels

Map showing additional heat-related deaths forecast between September 2026–February 2027 vs 1996-2025. Credit: Climate Impact Lab Heat during the strengthening El Niño could contribute to an estimated 451 000 additional deaths worldwide between June 2026 and February 2027, according to a Climate Impact Lab assessment released on September 23, 2026. The total includes 239 000 projected deaths during September 2026–February 2027. The estimates compare mortality with the corresponding months of an average year using a 1996–2025 baseline. The June–August component represents modeled mortality for months preceding the report’s release, rather than a verified count of deaths. For September–February, the report gives an estimate of 239 000 ± 11 000 additional deaths, equivalent to 228 000–250 000 under its stated uncertainty calculation. It defines the range as the mean plus or minus 1.96 standard errors. The analysis estimates excess mortality during the event against that historical baseline. It does not isolate the effect of El Niño from every other contributor to the anomalous heat. Impact Lab The brief estimates 66 800 additional heat-related deaths across the Sahel countries it identifies as most affected during September 2026–February 2027. That total includes 31 400 in Nigeria. The same six-month projections include 19 300 additional deaths in Indonesia and 19 400 across the Philippines, Vietnam, Thailand and Cambodia combined. Estimates for India and Brazil are 15 800 and 13 300, respectively. The assessment comes as the US National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center recorded a Niño-3.4 sea-surface temperature of 29.6°C (85.3°F) for the week centered on September 16. The anomaly was +3.0°C (+5.4°F), up from +2.9°C (+5.2°F) a week earlier and matching the value listed for November 18, 2015, at the dataset’s reported precision. The Washington Post reported a daily Niño-3.4 anomaly of +3.05°C (+5.49°F) on September 19, setting a new daily record in its analysis of NOAA’s Optimum Interpolation Sea Surface Temperature dataset. Impact Lab NOAA assesses seasonal El Niño strength using the Relative Oceanic Niño Index (RONI), which averages relative sea-surface temperature anomalies over three months and adjusts for conditions across the tropical oceans. A record in the daily Niño-3.4 anomaly does not establish a record under that index. NOAA’s September 10 ENSO Diagnostic Discussion maintained an El Niño Advisory and reported a greater than 90% chance of a very strong event during Northern Hemisphere autumn and winter 2026–27. For October–December, NOAA forecast a 75% chance that the three-month RONI would reach at least +2.5°C (+4.5°F). The agency said an event meeting that threshold would exceed previous events in its record dating to 1950. The assessment was prepared , Tamma Carleton, Genevieve Maricle and Emily Grover-Kopec of the Climate Impact Lab.