The sea surface temperature in a key section of the central equatorial Pacific Ocean has now surpassed all previous temperatures on record for this region, exceeding 86 degrees Fahrenheit (30 degrees Celsius) for the first time, according to preliminary data released Monday (Oct. 5).

Specifically, these temperatures occurred in the Niño 3.4 region, located between 5 degrees north and 5 degrees south latitude, and 120 degrees west and 170 degrees west longitude. Researchers use this region to monitor the progression of El Niño, the warm phase of a multiyear natural climate pattern that's currently in full swing and steadily intensifying. But how significant is this new record, and could it be a harbinger of increasingly extreme El Niño events in the future?

At this time of the year, sea surface temperatures above 86 F are common in the western Pacific warm pool, a mass of water located northeast of Australia. But the Niño 3.4 region is nowhere near the warm pool and usually has much cooler temperatures. This latest data indicates "an exceptionally warm state for this part of the tropical Pacific," said Jin-Yi Yu, a professor of Earth system science at the University of California, Irvine.

"If the reported daily El Niño 3.4 temperature above 30°C is verified in the observational dataset, it would be an extraordinary record," Yu told Live Science in an email.

Other experts agreed. A Niño 3.4 sea surface temperature above 86 F is a "very significant" new record, Timothy Osborn, a professor of climate science and the director of the Climatic Research Unit at the University of East Anglia in the U.K., told Live Science in an email. Mat Collins, a professor of climate systems and the head of mathematics and statistics at the University of Exeter in the U.K., also called the temperature "very significant" in an email to Live Science.

But it's important to note that absolute temperature is not the standard way of measuring the strength of El Niño, Osborn said. Researchers usually assess El Niño intensity by comparing sea surface temperatures in the Niño 3.4 region with the average conditions there or with sea surface temperatures across the rest of the tropics, with the latter method removing a skew in the data caused by the climate-change-induced heating of oceans globally.

"On those measures, the current event is already close to being the strongest [El Niño] on record and will likely soon exceed previous records given that the event is forecast to strengthen further," Osborn said. "For some measures, it is already record-breaking for the time of year."

"Super" El Niño

El Niño events happen when warm water in the western tropical Pacific Ocean migrates eastward along the equator, toward South America. This boosts global temperatures, triggering heavy rainfall and floods in regions like East Africa, southern China, the southern U.S. and the Pacific coast of equatorial South America, while places such as Indonesia, the Philippines, southern Africa and northern South America experience drought.

"El Nino impacts are greatest across the tropics and in the lands around the Pacific Ocean," Osborn said. "An El Nino with record strength is very significant because it greatly disrupts the atmospheric circulation which controls the weather patterns including patterns of rainfall."

As of Oct. 6, the temperature anomaly in the Niño 3.4 region is 6 F (3.34 C) above average and rising. A typical El Niño increases Niño 3.4 temperatures by a maximum of 1.8 to 3.6 F (1 to 2 C) above average, so the current condition is "exceptionally large," Yu said. "This indicates that a very strong, or what is sometimes called a 'super,' El Niño is developing."

This year's El Niño is being amplified by human-driven global warming, which has increased background ocean temperatures. As a result, it's likely that sea surface temperatures in the Niño 3.4 region will keep rising over the coming weeks and peak in November or December, before declining again in 2027, Collins said.

"The Niño 3.4 anomaly is very likely to remain extremely large and may increase further," Yu said, echoing forecasters' suggestions that it could reach 7.2 F (4 C) by November.

A new kind of El Niño?

The world is on the brink of crossing a critical warming threshold, raising the question of whether the current conditions can be considered a new normal for future El Niños.

While it's likely that future El Niños will be more extreme than past ones, on average, not every El Niño will be record-breaking and as dramatic as the one unfolding now, because these events tend to be very variable, Collins said.

As climate change intensifies, the big worry is that certain regions will be primed for extreme conditions even before an El Niño strikes, Osborn said. For example, regions that are getting drier due to global warming could see catastrophic droughts if they overlap with areas that experience dryness during El Niño events. Likewise, places that are getting wetter could see worse deluges of rain and flooding if they coincide with areas with higher precipitation during El Niños. But that doesn't necessarily mean extreme El Niños are the new normal, he said.

Instead, the location and duration of El Niño events may be transforming, Yu suggested. "In research by my group and collaborators, we have documented changes not only in El Niño intensity, but also in where the warming occurs and how long events persist," he said.

Yu and his colleagues helped to introduce the idea that we are seeing the emergence of two distinct types of El Niño: the eastern Pacific El Niño and the central Pacific El Niño. "Many El Niño events in the earlier observational record were dominated by warming in the eastern tropical Pacific, whereas Central Pacific El Niño events became much more prominent in recent decades," he explained, adding that El Niños have also been lasting longer.

Global warming may be creating a new kind of El Niño by strengthening atmosphere-ocean interactions in the subtropical Pacific, Yu said. If these interactions combine with processes in the equatorial Pacific, where eastern Pacific El Niños emerge, they might trigger unusually strong events with extreme heating in the central Pacific.

"That provides a physical reason to take the possibility of more frequent extreme El Niño events in a warmer climate seriously," Yu said. "But I would distinguish that from saying that every El Niño will become progressively stronger."

On Sept. 20, the Antarctic ozone hole peaked at 10.6 million square miles (27.4 million square kilometers), the second-largest size ever observed for this time of the year.

The last time the ozone hole was this big was in October 2015, when it reached a whopping 10.8 million square miles (27.9 million square km), records from the Copernicus Atmosphere Monitoring Service show. So why is the hole in the ozone layer — the shield that protects life on Earth from harmful ultraviolet solar radiation — so big this year, despite other clues telling scientists that it is recovering as expected from the damage human-made chemicals did in the 20th century?

The ozone hole's extent is due to extremely low temperatures in the stratosphere, but it's also possible that we could be seeing a new long-term trend of large, persistent holes, experts told Live Science.

"This year's ozone hole shouldn't be a cause for alarm," Hannah Kessenich, a postdoctoral physicist at the University of Otago in New Zealand who predicted the 2026 ozone hole's extent using satellite data and a computer model, told Live Science in an email. "However, there are still many unanswered questions. It's something we need to keep a close eye on."

Accurate predictions

The latest figures from the Copernicus Atmosphere Monitoring Service indicate that the size of Antarctica's ozone hole has dropped to around 8.9 million square miles (23 million square km) since Sept. 20, making it unlikely that this year will break the 2015 record. However, scientists think the hole will remain large and fluctuate over the next few weeks, Kessenich said.

Antarctica's ozone hole expands every year during the Southern Hemisphere's winter and spring. It typically reaches its maximum size between mid-September and early October, when temperatures are still freezing in the stratosphere and sunlight illuminates the frozen continent for the first time after months of darkness. The hole then shrinks again until late January as surrounding ozone-rich air mixes into the depleted region.

Antarctica's ozone hole was caused by emissions of ozone-destroying chlorofluorocarbons (CFCs) between the 1930s and late 1980s. These chemicals increased concentrations of chlorine in the stratosphere, thereby promoting a reaction that depletes the ozone layer. While countries signed the Montreal Protocol to phase out CFC use beginning in 1989, major CFCs have atmospheric lifetimes of 50 to 100 years, so the hole's recovery could take six decades, researchers estimate.

The ozone layer is particularly vulnerable above Antarctica due to the frigid conditions in the polar stratosphere. Temperatures below minus 108 degrees Fahrenheit (minus 78 degrees Celsius) trigger the formation of high-altitude clouds, whose icy surfaces turn inactive chlorine into its ozone-destroying form in the presence of sunlight. These conditions don't exist to the same extent in the Arctic, because warmer air from the midlatitudes mixes more readily with cold Arctic air than with Antarctic air, thereby blocking the formation of high-altitude clouds.

Changes in the polar vortex

This year's large ozone hole is caused by a very strong polar vortex, a wall of wind that encircles Antarctica and the Southern Ocean in the winter, trapping cold air above the continent. The polar vortex created colder-than-usual conditions in the stratosphere over Antarctica, accelerating the growth of the ozone hole.

Researchers haven't detected an increase in reactive chlorine, but the colder polar vortex has triggered more ozone depletion than usual, said Susan Solomon, a professor of chemistry and environmental studies at MIT who pioneered the study of Antarctica's ozone hole in the 1980s.

This size of this year's ozone hole is most likely a product of natural variability in atmospheric dynamics, Kessenich said.

"We expect ups and downs in the size of the hole from year to year," Solomon told Live Science in an email. "A year or a few years of bigger or smaller holes doesn't tell us anything about ozone loss or recovery; it is just variability. We have to look at the longer term trends, and those metrics continue to tell us that the ozone hole is slowly recovering as expected."

It's also reassuring that the ozone hole, while large, isn't as "thin" as in years past. The hole's extent is calculated based on the area above the continent with ozone values below 220 Dobson units, a measure of how many ozone molecules occur in a vertical column through Earth's atmosphere. Although the area of this year's ozone hole is huge, ozone values haven't dropped as low as in previous big-ozone-hole years, suggesting that there is less ozone "missing" from the hole compared with those years, Kessenich and her colleagues wrote in The Conversation.

But there's also the possibility that we've shifted to a new long-term trend of big ozone holes persisting until late spring, Kessenich said. Changes in global atmospheric dynamics unrelated to CFCs could be making longer-lived holes more likely, she and her colleagues wrote in the article.

There is also some evidence that climate change will strengthen the Antarctic polar vortex over time, which could lead to colder temperatures in the stratosphere and greater ozone losses in the spring, Kessenich said. If this year's polar vortex stays robust, the ozone hole could remain large well into November, she noted.

"It's too soon to tell what has been driving dynamical variability in recent years, but more research is needed," she added.

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