Summer 2024 Was the Hottest Ever Measured, Beating Last Year

Summer 2024 Was the Hottest Ever Measured, Beating Last Year

By Saima S. Iqbal

In Japan more than 70,000 people visited emergency rooms for heat stroke this July and August alone. In Iran an unrelenting heat wave shuttered government agencies, banks and schools. And in the U.S. cities such as Phoenix, Ariz., and Las Vegas endured high temperatures above 100 degrees Fahrenheit (38 degrees Celsius) for weeks on end. These were just some of the markers of what European and American climate agencies have found to be the hottest June to August on record—and they offer a peek at how further warming could transform the planet.

This new summer record, an average temperature of 62.2 degrees F (16.8 degrees C), beats out last summer’s extraordinarily high average by a narrow 0.05 degree F (0.03 degree C). Both constitute the highest two summer averages in annals that go back to 1850. But studies of ancient tree rings suggest that 2023’s temperature—and by extension 2024’s—were the hottest in the past 2,000 years. And some climate scientists calculate that these two years’ summer averages could even be the highest in 125,000 years; that far back in Earth’s history, hippos swam in the waters around Great Britain., and forests dotted the Arctic. The U.S. National Oceanic and Atmospheric Administration’s National Centers for Environmental Information now says there is a 97 percent chance that 2024 will beat 2023 as the hottest full year on record as well.

A blistering June and August contributed in large part to this summer’s record. Both months broke or matched heat records from 2023, with average global surface area temperatures exceeding preindustrial levels by at least 2.7 degrees F (1.5 degrees C). In 2016, under the Paris climate accords, countries agreed to try to keep global warming below this threshold—though that goal considers a multiyear average, not single months. Had July been a tad hotter, the planet could have laid claim to a 14-month streak of such threshold-passing temperatures. (July did see the hottest day on record, however: on July 22 the global average temperature reached 62.89 degrees F, or 17.16 degrees C, about three degrees F, or 1.7 degrees C, above preindustrial averages.) This year 15 countries ranging from Mexico to Chad reached all-time high temperatures; 130 national monthly records have also been broken.

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Such a record of records reflects the magnitude of human-induced climate change. Global temperature records do cluster around El Niño events, the most recent of which began in late 2023 and ended in May 2024. This complex climate pattern leads to considerable heat being released from the tropical oceans into the atmosphere. But El Niño only contributes 0.36 degree F (0.2 degree C) of variation to the global temperature and alone could not produce the rapid changes the planet is now undergoing. “Human emissions of greenhouse gasses effectively add a permanent El Niño worth of heat every decade,” says Zeke Hausfather, a climate scientist who works for the nonprofit Breakthrough Institute. Other unknown factors appear to be in play as well, he notes, because scientists believe up to one third of the planet’s observed warming throughout 2023 and 2024 is not accounted for by human-made climate change or El Niño.

Earth has endured more extreme temperatures in the past, but those extremes built up more gradually. “These are geological trends that usually take millions of years or thousands of years to happen,” says Angel Fernández-Bou, a biosystems engineer at the University of California, Merced. “Now that [same] increase of temperature happens over decades.” As a result, scientists worry that the planet is warming far too quickly for living things and their environments to adapt.

Modern sewers, for instance, might not withstand the increasingly intense rains. Our body won’t be able to tolerate as much time outdoors—or indoors without air-conditioning—as heat waves grow more intense and frequent. Increasing wildfires are expected to raze thousands of acres of crops and grazing lands. And past adaptation measures have proven more slow going and costly than previously imagined, Hausfather points out.

Though global and national temperature records offer clear signs of how much excess heat greenhouse gases have trapped in the atmosphere, real people do not live in average temperatures. Such measurements can mask wide regional variations and extremes. In the U.S. Southwest, successive summer heat domes created one of the hottest places on the planet: As of September 4, Phoenix had reached 100 degrees F for more than 100 days in a row. This blew the city’s previous record of 76 consecutive days, set in 1993, out of the water. A July heat wave burdened Olympic athletes in Paris, spread wildfires in Portugal and Greece and worsened water shortages in Italy and Spain. Even the Southern Hemisphere, where it was winter, sweltered throughout June to August. Across Australia, it often felt more like summer, with national temperatures 5.4 degrees F (three degrees C) above normal throughout August—and one remote region in Western Australia reaching a record of 107 degrees F (41.6 degrees C). In July regions of winter-bound Antarctica rose 50 degrees F (28 degrees C) above typical temperatures.

The planet will continue to blast through heat records until humans stop producing greenhouse gases, says Andrew Dessler, a climate scientist at Texas A&M University. With renewable energy now cheaper than fossil fuels, the largest hurdle to meaningful action is not technological but political, he says. This means “the solution is in our grasp,” Dessler emphasizes.

Greenhouse gas emissions have held steady over the past decade, at least preventing further acceleration of warming. Stopping global temperatures from rising even more, however, will require putting an end to emissions from the burning of fossil fuels and from other sources such as deforestation and agriculture. Climate scientists now project that the planet will pass the 1.5-degree-C threshold set by the Paris accords later this decade or early next.

“But it’s not like the climate goes from fine to on fire as soon as the world passes 1.5,” Hausfather emphasizes. “Every tenth of a degree matters; the higher the warming, the worse the impacts.”