A new report estimates that the unusually strong El Niño event could cause 451,000 additional heat deaths between June 2026 and February 2027.

The estimate, reported by the Guardian, was produced by researchers linked to the Climate Impact Lab and the University of Chicago. It combines month-by-month relationships between temperatures and heat deaths in 24,378 regions with forecasts for the months ahead.

The countries projected to be most affected include Nigeria, Indonesia, Sudan, India and Brazil. The United States is in the top 20, with about 3,500 additional heat deaths projected.

The figure is a forecast, not a confirmed toll. The report is being submitted to a peer-reviewed journal, and its authors released the estimate before peer review because they said the public-health stakes justified immediate attention. The period was corrected from September 2026–February 2027 to June 2026–February 2027.

The report also points to the way climate risk compounds existing inequality. Heat exposure is shaped by housing, work, access to cooling, health systems and the ability of governments to issue warnings and respond.

The useful question is not whether the projection will land on a single exact number. It is whether governments can use the warning to target heat action plans, health-system capacity and food-security measures before the next dangerous season arrives.