This Summer Could Be Even Hotter

There are still a few days left, but this month is on track to be the warmest May ever documented. In fact, every month since last June has broken worldwide temperature records. The world’s oceans, which were too hot last year, are still mostly too hot now. The combination of manmade global warming, an unnatural climate phenomenon, and El Niño, a natural one, has inflated temperatures around the globe over the past year; the current El Niño event, which emerged in the middle of 2023, has been among the strongest on record. This El Niño, at least, is nearly done—but its end likely won’t save the Northern Hemisphere from another sweltering summer.

El Niño episodes last only about nine to 12 months at a time, and forecasters predict that its cooler opposite, La Niña, will settle in sometime between this summer and early fall. La Niña should eventually lower the planetary thermostat, Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration who studies the twin phenomena, told me. But a worrying amount of climate chaos still awaits us as La Niña asserts itself in the next several months, and the relief it may bring will be only temporary in the grand scheme of our warming world.

The transition to La Niña is not a flipped switch; the excess heat of El Niño conditions takes time to dissipate. As a result, “there’s a high likelihood that 2024 will be even warmer than 2023 because of this delayed effect,” McPhaden said. “La Niña may bring some relief, if not this year, then perhaps in 2025.”

For many people, though, 2025 is too far away. Right now, Southeast Asia is suffering from extreme heat. Europe is set to experience another brutally hot summer. In parts of the United States, heat-related health emergencies reached historic levels last summer, and we may experience a repeat this year. Some parts of Florida have already registered heat indexes—the “what it actually feels like” measure, combining air temperatures and relative humidity—well above the danger threshold this year, and it’s still spring.

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The extreme heat in Florida isn’t limited to land. Along its coasts, a marine heat wave caused massive coral bleaching last year, and marine scientists are not hopeful about this year either. Historically, such events were limited to August. But “last year, it all started in early July, and now this year, we’re seeing temperatures hit August levels in the middle of May,” Derek Manzello, a coral biologist and the coordinator of NOAA Coral Reef Watch, told me. “La Niña really can’t come soon enough,” he said, because “it should basically stop the bleeding.”

But for Florida especially, the transition to La Niña is its own kind of danger. During La Niña, high-altitude winds that might tear apart hurricanes in El Niño years weaken instead. So more storms spin into existence and strengthen on their way to land. To make matters worse, hurricanes intensify by feeding off warm seawater—and plenty of that is available in the Atlantic right now. The combination of La Niña and abnormally hot oceans is expected to produce a perilously strong hurricane season for the Eastern Seaboard, the Gulf Coast, and the Caribbean.

Both El Niño and La Niña deliver grief to some regions of the world—heavy rains, intense storms, droughts, wildfires—and a reprieve to others. In Canada, “we want to move from El Niño to La Niña,” Hossein Bonakdari, a University of Ottawa professor who specializes in the effects of climate change on civil-engineering infrastructure, told me. That’s because Canada experienced a staggeringly destructive wildfire season last year, and La Niña likely will bring much-needed rainfall that can reduce the risk of blazes. Meanwhile, “California loves El Niño because that rescued us last year from the drought,” Alexa Fredston, a quantitative ecologist at UC Santa Cruz, told me.

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And human-caused climate change is amplifying the effects of both phenomena. “In a warmer world, the atmosphere can hold more moisture,” McPhaden said, so El Niño– or La Niña–caused rainfall that might once have been severe instead becomes extreme. A warmer atmosphere also increases the rate of evaporation of water on land, so severe droughts turn into extreme droughts, too.

Climate change also risks dampening the relief that La Niña has historically brought to regions warmed by El Niño. Manzello worries that La Niña won’t be enough to keep corals from bleaching this time, even moving into next year. “How much help is it really going to bring now that the global ocean is just so darn hot?” he said. La Niña’s cooler temperatures curb the formation of harmful algal blooms, which can be toxic to people, animals, and aquatic ecosystems, Julian Merder, a postdoctoral researcher at the Carnegie Institution for Science, told me. But what happens if global warming nudges temperatures into algae’s preferred zone even during the cool phase? Such blooms thrive in warm temperatures and on nutrients flushed from land by heavy rains and runoff. Historically, El Niño has provided both of those conditions. But in a warmer world, heavy snowpack from a La Niña winter would melt during springtime into hotter conditions, making trapped nutrients available to algae. “It might even be the case that La Niña is getting us more harmful algal blooms than El Niño would,” Merder said.

The La Niña that perspiring Americans might long for now is not what it used to be. “La Niña years now are warmer overall on the planet than big El Niño years were 25 years ago,” McPhaden said. Both climate phenomena have always been powerful. But in the 21st century, the cool phase is only a temporary antidote to the symptoms of climate change, and a fainter one at that. If greenhouse gases continue to warm our world, La Niña’s reprieve will only grow weaker.