The images are spectacular: Exhausted after weeks of exposure to temperatures above 50°C (122°F) in the southeastern Mexican state of Tabasco, howler monkeys fall from trees in a state of dehydration. Despite the efforts of locals to save them, the authorities reported that at least 164 of these primates had died in May. "Temperatures have never risen to this level for so long," said a vet who took part in monkey rescue brigades in the jungle around the town of Comalcalco.

For over a month, Mexico has been experiencing its third heat wave of the year, thanks to a high-pressure system that is preventing cloud formation and exposing the country to the sun's rays. The temperature has regularly exceeded 45°C (113°F) in 19 of the country's 32 states, and the Ministry of Health has attributed 61 deaths to the heat. Despite scattered rainfall in recent days, more than 70% of the country is still suffering from varying degrees of drought, and 4,650 fires were recorded in the first half of the year, 132 of which are still burning.

"Temperatures in 2024 will beat all historical records, not only because of their intensity but also because of the duration and extent of the heat wave, which is affecting almost the entire territory," said Jorge Zavala, director of the Institute of Atmospheric Sciences and Climate Change at the National Autonomous University of Mexico. The expert is concerned about the effects of extreme heat on health, not least because the majority of homes are not equipped with adequate ventilation systems to withstand these extreme conditions.

In Mexico City, where the heat reached a peak of 34.7°C (93,2°F) on Sunday, May 26, for the first time in a century of weather records, the air is all the more stifling as the megalopolis has been on almost permanent pollution alert in recent weeks, owing to the high concentration of ozone in the atmosphere.

The authorities have restricted car use to cope with the build-up of this pollutant, which increases the heat and affects the respiratory system, and exhorted the capital's 9 million inhabitants (20 million including the greater suburbs), to go out as little as possible, not to engage in outdoor physical activity and not to fill up with petrol during the afternoon.

In the state of San Luis Potosí, in north-central Mexico, some hospitals have been overwhelmed by the large number of patients suffering from sunstroke. The high demand for energy from air-conditioning systems has put a strain on the national power system, forcing the government to schedule overnight blackouts to make up for the lack of electricity. The authorities have estimated that two further heat waves could occur between now and the end of June.

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