On Labor Day, you could drive from Minnesota’s border with Canada all the way to where Louisiana hits the Gulf of Mexico and not encounter a high under 90 degrees. The heat hasn’t broken: Today, nearly a third of Americans are sweltering under heat alerts.
Such weather is a fitting end to a devastating season, the kind you run out of superlatives for. This summer, climate extremes suddenly seemed to be everywhere, all at once. It was the world’s hottest June since humans started keeping track. July was even worse. Phoenix—which averaged 102 degrees in July—got so hot that people received third-degree burns from touching doorknobs. In Iowa, livestock dropped dead in their pens. The disasters weren’t limited to heat: Canadian wildfires blanketed large swaths of the United States in smoke, flash floods thundered through Vermont, and wildfires reduced parts of Maui to rubble.
Pumpkin spice is already back on the Starbucks menu, but fall isn’t poised to provide a respite. El Niño, the warm phase of a naturally recurring cycle that can wreak havoc on global weather patterns, has officially returned—and it’s predicted to be a strong one. The southern U.S. will likely be wetter, while forecasts are for a warm winter in the North. These cycles always have some variability, but experts say that the climate crisis has now raised temperatures to the extent that they may also amplify El Niño. This summer has shown starkly how climate change can supercharge the weather. This fall, El Niño could further magnify the problem.
Although El Niño technically started in June, it likely didn’t contribute much to this summer’s extremes. That was the climate crisis. Across the U.S., hundreds of temperature records fell. Kansas City’s heat index approached that of Death Valley. Chicago had to reduce its trains’ speeds because high temperatures stressed the tracks. “Historically, El Niño events during the summer have very little impact over the United States,” Michelle L’Heureux, a climate scientist at the National Oceanic and Atmospheric Administration, told me. “Climate change, however, is having an impact.” Scientists once hesitated to say how global warming might worsen weather. Now they can accurately measure just how much climate contributes to events such as heat waves. An international team of researchers found that climate change made July’s heat waves in the U.S., Europe, and China hotter by as much as 2 degrees Celsius, or 3.6 degrees Fahrenheit, as a result of climate change.
After this summer’s extremes, it’s daunting to be entering the height of an El Niño cycle. Typically, because of the direction the world spins, winds move from east to west across the tropics. This blows warm surface water away from South America, where colder water swells up to replace it. But every two to seven years, these winds weaken and more warm water remains along the Americas—producing El Niño. (When the winds strengthen, you get its counterpart, La Niña.) The Pacific Ocean is huge, covering a third of the Earth, so these cycles can cause dramatic variations in global storms and droughts. That’s why L’Heureux calls El Niño “the Great Nudger.” As she explains, “It nudges atmospheric patterns over the globe in certain directions that cause weather patterns to reoccur.”
Unlike during La Niña, when a cooler ocean can absorb more heat, El Niño basically acts as a temporary boost to global warming—bumping global temperatures up by around a tenth of a degree Celsius, or roughly 0.2 degrees Fahrenheit. The effects, however, vary by location: Some places become colder, while others become much warmer. A strong El Niño during the winter of 1997–98, for example, caused flooding in California, while Indonesia and the Philippines suffered under a severe drought. In 2016, another record El Niño contributed to what is still officially the world’s warmest year on record; NOAA estimates it raised the annual global temperature 0.12 degrees Celsius, or 0.2 degrees Fahrenheit, above average.
The influence of El Niño is also potentially intensifying because of climate change. Warmer air holds more moisture, setting the stage for more extreme precipitation; likewise, hotter temperatures may worsen the drought conditions it already tends to bring to some locations. “El Niño impacts do not work in isolation anymore. There’s always a climate component,” L’Heureux said.
Unless you’re a mosquito in New Mexico, that is not good news for the fall and winter. Right now, satellites, sensors, and models suggest that ocean temperatures are gradually increasing, as the cycle gathers strength. El Niño’s impacts will be most visible later this fall and into winter 2024. (It’s called El Niño, or “little boy” in Spanish, after the newborn Christ, because the cycle tends to peak around Christmas.) At that point, much of the southern U.S. will likely see wetter conditions. Meanwhile, the Pacific Northwest is predicted to be drier, while the northern part of the country may have a balmy winter. “Because it’s a climate forecast, and we can’t say anything definitively, we put probabilities on everything,” L’Heureux said.
Based on past El Niños, the U.S. may be in for more climate extremes. In 1997–98, for example, California saw 150 percent of its normal rainfall, washing away roads and producing deadly, home-destroying mudslides. The Midwest practically had no winter, with some areas experiencing average temperatures 12 degrees warmer than in a normal year. Some may cheer a milder fall and winter, but that might also heighten the risk of troubling heat deeper into September and October. And warmer temperatures could set the stage for worse wildfires next summer. That’s not to mention all the other downstream effects from knocking normal patterns out of whack. In 2016, for example, a cool, wet spring was great for fleas and other disease-carrying insects, increasing cases of plague and West Nile in the Southwest. Going back to 1982–83, unseasonable heat in Alaska was likely behind the reduced salmon harvest, while warmer waters caused a rash of shark bites off the Oregon coast.
Nor, of course, is El Niño merely a U.S.-specific problem. Just like with climate change, developing countries are often hit the hardest. Petteri Taalas, secretary-general of the World Meteorological Organization, warned that as a result of El Niño, the coming months may have “far-reaching repercussions for health, food security, water management and the environment.” The sum total of heat could cause global temperatures to surge past an infamous benchmark—1.5 degrees Celsius warmer than the preindustrial era, topping records set during the last El Niño in 2016.
L’Heureux leads the El Nino-Southern Oscillation team at NOAA’s Climate Prediction Center, and her team predicts that El Niño has a more than 95 percent chance of lasting through February 2024. After that, it’s hard to say. El Niños typically persist for about a year, but the exact timing and intensity of each cycle can vary. In a warmer future, El Niños may stretch longer. A recent Nature paper suggests there’s some early evidence that the transitions between El Niño and La Niña phases may be slowing down—which means that the conditions associated with them could stick around. The Pacific Walker Circulation, a massive atmospheric loop over much of the tropics, helps dictate these transitions, and many models project that climate change will weaken this loop. As a result, “instead of single years of El Niño or La Niña conditions, we may experience more multiyear events,” says Georgina Falster, the paper’s lead author. Think extended droughts, more summers with weeks-long heat waves.
These are complicated systems, and many parts of the El Niño cycle still aren’t well understood. But figuring out how these cycles may be changing is important, because climate models rely on our best attempt at describing current conditions in order to make assumptions about how the world might change. If the assumptions aren’t accurate, they could alter our forecasts for climate impacts. “There’s a lot of uncertainty” with these models, L’Heureux said. That’s true of how we experience climate change too. The weather in any given year can have a lot of variability, a point Senator James Inhofe’s congressional snowball accidentally made. Climate change may not always feel linear—this past summer, its impacts felt like they fast-forwarded. A hot winter, fueled in part by El Niño, doesn’t necessarily mean next summer will be even worse. But in the long term, the trend of higher temperatures is undebatable.
Disconcertingly, this is all still just the overture to a world that looks very different from the one we’ve known to date. Allegra LeGrande, a physical-research scientist at the NASA Goddard Institute for Space Studies, told me that by the time her young children are in their 40s, “they won’t have a summer as cool as the summer has been.” Though researchers have predicted dire climate consequences for decades, many of the scientists I’ve spoken with this summer have wrestled with how to feel about the recent drumbeat of broken records. For her part, LeGrande has been coping by bingeing survival shows like Alone that drop contestants in the wilderness to see how long they can withstand the elements—a cinematic version of the shifting reality many are already starting to face off-screen.
No matter how much you study or read about the climate crisis, it hits differently when you have to confront it every time you walk outside. After this summer’s strangeness, the science may be complicated, but the conclusion is simple: Even when this El Niño dissipates and the world returns to a cooler phase, it won’t be enough to counteract the march toward a hothouse Earth. Only we can do that.