El Niño could cause more than 850,000 heat deaths by March 2027, scientists estimate

The ongoing strong El Niño could cause around 857,000 extreme heat-related deaths worldwide by March 2027.

The estimate is from the Climate Impact Lab, a group of researchers linked to the University of Chicago, in the United States, which updated its projections in a new monitoring tool released this Tuesday (27).

The number is almost double the previous estimate, of approximately 451 thousand deaths, presented by scientists in September. The new projection considers the period from the beginning of the phenomenon, in June 2026, until March 2027.

Of the estimated total, around 373,000 deaths are expected to occur in the next six months, between October this year and March 2027.

The survey also points out that Brazil could record approximately 19,000 heat-related deaths above average during this period.

The number of deaths associated with high temperatures is expected to be above average in all months of the projection.

Global South should concentrate the biggest impacts

The report shows that countries in the Global South are expected to concentrate the majority of heat-related deaths over the next six months.

Among the countries with the highest projections are Nigeria, with around 56 thousand deaths, India, with approximately 55 thousand, and Indonesia, with 29 thousand.

Brazil also appears among the affected countries, with an estimated 19,000 additional heat-related deaths between October 2026 and March 2027.

The projections reflect not only exposure to high temperatures, but also differences in the vulnerability of populations and the adaptation capacity of each region.

Why did the death estimate increase?

According to the Climate Impact Lab, two main factors explain the increase in relation to the projection released in September.

The first is the inclusion of March 2027 in the analyzed period, which allows us to consider more months of duration of El Niño impacts.

The second is the replacement of temperature forecasts for August and September with data actually observed in those months. Temperatures recorded were higher than initially projected.

August 2026 was the hottest ever recorded for the month, while September came in second place in the historical ranking, according to the data considered by the researchers.

New tool tracks deaths by region

The update was accompanied by the launch of a tracker that allows viewing the geographic distribution of heat impacts associated with El Niño.

The tool presents monthly estimates of deaths in around 3,700 administrative regions – such as states and provinces – in different countries. It also brings together data on heat-related deaths since the phenomenon began in June.

Projections are updated monthly and should continue to be released until the end of the current El Niño episode.

To calculate the estimates, researchers use models that relate daily temperature to all-cause mortality, taking into account differences in local climate, population vulnerability and the adaptation capacity of each region.

Scientists combine data on previously observed temperatures with climate forecasts for the next six months. The result is an estimate of additional heat-related deaths compared to the historical average.

According to the group, the data can help governments and organizations identify the most vulnerable regions and direct prevention measures, such as warning systems for heat waves, expanding access to healthcare, creating cooling centers and protecting workers exposed to high temperatures.

The team highlights that targeted actions can prevent tens of thousands of deaths during the phenomenon.