Climate Crisis Made Deadly Heatwave in US and Mexico 35 Times More Likely

Scientists on Thursday released an analysis showing the likely role of climate change in creating the deadly heatwave that hit areas including Mexico and the U.S. south in late May and early June.

Record-breaking heat caused by a heat dome, which engulfed areas from Nevada to Honduras, was hotter and more likely to occur due to the climate crisis, with five-day maximum daytime temperatures 35 times more likely than in pre-industrial times and nighttime temperatures 200 times more likely, scientists at World Weather Attribution (WWA) found.

At least 35 died of related illness in just one week in early June in Mexico, and the total death toll may have been much higher. The scientists emphasized that the extreme weather causing the death and suffering was brought about by fossil fuel emissions.

"Unsurprisingly, heatwaves are getting deadlier," Friederike Otto, a co-author of the study and climate scientist at Imperial College London, told The Guardian. "We've known about the dangers of climate change at least since the 1970s. But thanks to spineless politicians, who give in to fossil-fuel lobbying again and again, the world continues to burn huge amounts of oil, gas, and coal."

The analysis was published on the same day that the Energy Institute reported that fossil fuel consumption climbed to a record high in 2023, with coal, oil, and gas still making up more than 80% of the global energy mix, though the figure fell below 70% in Europe for the first time.

May was the 12th consecutive month that was the hottest on record globally, compared to the same time period in previous years. And June has proved to be dangerously hot in many areas, with hundreds dying in the Hajj pilgrimage in Saudi Arabia as temperatures rose above 124°F and Balkan countries, as well as much of the U.S., currently under extreme heat advisories.

The WWA scientists sought to connect the May-June heatwave to these larger trends, and repeatedly explained the cause of the problem.

"As long as humans fill the atmosphere with fossil-fuel emissions, the heat will only get worse—vulnerable people will continue to die and the cost of living will continue to increase," Izidine Pinto, a co-author and researcher at the Royal Netherlands Meteorological Institute, told The Guardian.

The heatwave coincided with a drought in Mexico, exacerbating already dire conditions as water supplies dwindled and electricity systems faltered. It also followed, and may have helped prolong, a terrible outbreak of dengue in Latin America and the Caribbean that caused over 1,800 deaths. "Every heatwave is a push that builds up dengue transmission," an expert told Scientific American in April. Dengue cases have begun to decline but still persist, according to Dialogue Earth.

The May-June heatwave was notable for especially high nighttime temperatures, which prevent the body from resting and recovering from the daytime heat—a process that's only possible below about 80°F. Certain places in the study area saw nighttime temperatures "with return periods of up to 1000 years."

The climate crisis is changing the likelihood of such weather. "The extreme heat slamming the eastern U.S. this week may be a sign of things to come," The Hill's Zach Budryk wrote Thursday.

That was similar to the message of the WWA scientists.

"These trends will continue with future warming and events like the one observed in 2024 will be very common in a 2°C world," according to their analysis, which refers to a time when the planet has heated 2°C above preindustrial levels; it's already heated up by more than 1°C.

In the analysis, the authors called for warning systems, action plans, laws to protect outdoor workers, and other resilience measures such as better grid systems and more green spaces.