A science-fiction trope is the time traveler who visits the present day with a dire warning about the future only to be tragically ignored. It resonates because it’s so believable. In fact, Earth had just such a visitor recently, and we dismissed it completely. Three years ago, scientists warned that an approaching El Niño in the Pacific Ocean could temporarily boost global temperatures past 1.5 degrees Celsius above preindustrial averages, offering a taste of what the world would be like if we breached that long-term limit set by the Paris accords in 2015. Naive climate columnists wondered whether this would be enough to scare people into doing more to avoid that future. As expected, the El Niño of 2023 and 2024 delivered record-smashing temperatures. It was indeed frightening. And Americans responded by putting a virulent climate-change denier back in the White House, one whose stated goal was to burn more of the fossil fuels heating up the planet. Meanwhile, the political will to cut greenhouse-gas emissions flagged elsewhere in the world. El Niño is likely to return this year,