Earth just sweltered through the hottest day ever recorded

July 21 was an unprecedented day, and not just because President Joe Biden dropped out of the presidential race so close to the election. July 21 was the hottest day on record, according to the Copernicus Climate Change Service, with a global average temperature of 62.76 degrees Fahrenheit, slightly beating out the previous record set on July 6 of last year.

For 13 straight months now, the planet has been notching record temperatures, from hottest year (2023) to hottest month (last July). And what was a daily temperature record eight years ago has now become worryingly commonplace. “What is truly staggering is how large the difference is between the temperature of the last 13 months and the previous temperature records,” said Carlo Buontempo, director of the European Union’s Copernicus service, in a statement. “We are now in truly uncharted territory and as the climate keeps warming, we are bound to see new records being broken in future months and years.”

The territory may be uncharted, but the causes of this heat are abundantly clear. For one, there’s the steady rise of global temperatures due to carbon emissions. Since 1850, the Earth’s temperature has risen by 0.11 degrees F per decade on average, but that rate of warming since 1982 has jumped to 0.36 degrees per decade. Last year was already the hottest year on record by far, while 10 of the warmest years have all happened in the last decade. Copernicus also notes that before July 2023, the daily global average temperature record was 62.24 degrees F, on August 13, 2016. But since July 3, 2023, 57 days have exceeded that mark. Uncharted territory, indeed.

The world may also be feeling the lingering aftereffects of El Niño this summer. That’s the band of warm Pacific Ocean water off the coast of South America, which sends additional heat into the atmosphere that raises temperatures and influences weather patterns. The most recent El Niño peaked around the new year, then faded through this spring. “The atmosphere knows no boundaries,” said Shang-Ping Xie, a climate scientist at the Scripps Institution of Oceanography in San Diego. “We’re still under the influence of El Niño. Not to mention that North Atlantic warming is one of the reasons that this Atlantic hurricane season is expected to be very active.”

So while July 21 might have been sweltering for landlubbers, the parts of the Atlantic Ocean where hurricanes form are also extremely hot. Those warm waters are what fuel cyclones like Hurricane Beryl, which slammed into Texas earlier this month and left hunger in its wake. Scientists have forecasted five major hurricanes and 21 named storms this season, thanks in part to those high ocean temperatures.

There might also be some natural variability thrown into the mix this summer: Some years are just hotter than others even in the absence of human-caused warming. And this time of year is when global average temperatures naturally peak, as the Northern Hemisphere summer starts to mature. (More landmasses in the North absorb and emit the sun’s energy, versus all that ocean area in the South that helps cool things down.

“It just so happened that we had a spike on top of what is typically the warmest climatological week of the entire year,” said Zeke Hausfather, a research scientist at Berkeley Earth, which does its own climate analyses. “This is the warmest day on record, but also July is now — at least in my analysis — almost certain to not be the warmest July on record.” That is, the 13-month streak of records may well come to an end. Last July was so hot, it set a very high bar for future Julys to beat.

At the same time, by Hausfather’s calculations, there’s a 95 percent chance that 2024 will edge out 2023 as the hottest year ever. “It’s just been so warm in the first six months of the year that even if we don’t set new records for the second six months, we’re still very likely going to end up above 2023,” Hausfather said. “We’ve just built up that much of a lead already.”

Back in the Pacific Ocean, though, relief may be on the way: With El Niño gone, its cold-water counterpart, La Niña, could form in the coming months. That may help bring down global temperatures in 2025, and maybe even beyond. “The last La Niña was a three-year event,” Xie said. “That is of course very rare, but has extraordinary effects on the climate.”

Regardless of El Niño and La Niña, though, the past year has been exceptionally hot — an ominous sign that the planet hasn’t just entered uncharted territory, but an increasingly perilous one.