As a year of surprising global warmth came to a close, a record high annual average temperature was already assured. Now, some scientists are already speculating: 2024 could be even hotter.

After all, vast swaths of Earth’s oceans were record-warm for most of 2023, and it would take as many months for them to release that heat. An intense episode of the planet-warming El Niño climate pattern is nearing its peak, and the last time that happened, it pushed the planet to record warmth in 2016.

That suggests there will be no imminent slowdown in a surge of global warmth that has supercharged the decades-long trend tied to fossil fuel emissions.

It could be enough to, for the first time on an annual basis, push average planetary temperatures more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial, 19th century levels, according to Britain’s Met Office. The planet came closer than ever to that dreaded threshold in recent months, providing a first glimpse of a world where sustained levels of that heat would fuel new weather extremes.

But such climate trends can be difficult to predict with precision. After all, at the start of 2023, scientists predicted the year would end as one of the planet’s warmest on record. They didn’t expect it to set so many new precedents — and by record-wide margins.

“The fact that we are in uncharted territory, we don’t actually know what will happen next,” said Carlo Buontempo, director of the European Union’s Copernicus Climate Change Service.

The El Niño factor

El Niño is known to raise planetary temperatures by as much as a few tenths of a degree Celsius, a decent margin for a globally averaged statistic. That’s because it’s associated with warmer-than-average surface temperatures across the central and eastern Pacific Ocean, and those waters release heat and steam into the atmosphere.

El Niño typically lasts a year or less, peaking during the winter months and then fading in the spring. While scientists say no two El Niño events are exactly alike, each one brings some predictability to global climate patterns like few other planetary phenomena.

The current El Niño, which began in June, is considered strong and could peak as a historically potent episode some time in the coming weeks or months. It could be on par with a strong El Niño that began in early 2015, peaked that December, and faded by June 2016, on the way boosting 2016 to record warm global warmth.

If that pattern holds true this time, that could mean record warmth that has persisted over the past six months surges even higher in the first half of 2024.

One reason El Niño’s warming effect tends to crescendo in its latter months ties back to the effects it has on global weather. The abnormal sea surface warmth and storminess El Niño brings to the central and eastern Pacific has domino effects that lead to drought in other parts of the world, including Indonesia, southeast Asia and southern Africa.

“That sets the stage for higher than normal temperatures over land,” perhaps peaking around February, Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research, said in an email. “I expect this to be the case at least for the first 6 months of 2024.”

A momentous warming trend

Whether that warming influence dominates all of 2024 depends on what comes after the current El Niño fades. That is likely to occur by June, returning the Pacific to what climate scientists call neutral conditions — the absence of either El Niño or its foil, La Niña.

Beyond that, it’s not clear if neutral conditions will persist, or if La Niña — known for planetary cooling — will develop. El Niño could even return.

So far, there is no clear hint of what could be ahead. While this El Niño has in some ways developed according to scientists’ textbook understanding of the phenomenon, in other ways it has been difficult to categorize. Some pattern changes that climate scientists would normally expect to see as El Niño winds down have not yet developed, Trenberth said.

“There are some aspects of what is going on that remain puzzling,” Trenberth said. “Climate change means all past analogs are not so reliable.”

Human-caused climate change has indeed dominated global trends: The last eight years have been the eight hottest on record. A sure-to-be-record-hot 2023 and a potentially even hotter 2024 would stretch that streak to a decade.

Regardless of how the climate fluctuates this year, El Niño’s warmth across the Pacific will continue to influence global temperatures and weather patterns heavily, said Andrew Kruczkiewicz, a senior researcher at the International Research Institute for Climate and Society at Columbia University.

“It takes time for that energy to dissipate,” he said. “There’s persistence in the climate system.”