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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At the end of a glacier deep in East Antarctica's Taylor Valley, there is a haunting waterfall that oozes red brine like a bleeding wound in the ice. Scientists explained the brine's gory hue several years ago, finding that it is exceptionally rich in iron. And now, they may have identified the salty water's origin.

Microbes in the crimson waterfall, called Blood Falls, suggest the brine is composed of ancient seawater that was trapped in a pool beneath the glacier when ocean levels fell and the glacier advanced. However, it's unclear exactly when that happened, researchers noted. Previous studies had already proposed a seawater origin for the brine, based on various chemical signatures and bacteria detected in the liquid, but the new results add molecular and genetic evidence to the mix of clues.

"Findings in this study reveal a dominance of marine eukaryotic lineages in the Blood Falls area" compared with the broader region, known as the McMurdo Dry Valleys, the authors wrote in the study, published Monday (Aug. 3) in the journal Nature Geoscience. "This marine signal is less prominent but still detectable in the prokaryotic structure," the researchers added.

Eukaryotes' cells contain a membrane-bound nucleus and other closed internal compartments. Prokaryotes, by contrast, are single-celled organisms whose DNA floats around freely in the cell, unbounded by a membrane.

To characterize the types of microorganisms present within Blood Falls, the researchers used a suite of genetic techniques to analyze 167 samples of water, sediment and air from around the falls and the broader McMurdo Dry Valleys.

Some researchers argue that Blood Falls' water does not originate from seawater, and suggest the marine bacteria and chemical signatures that point to seawater may have instead reached the falls from the ocean via intense winds, which are common in the McMurdo Dry Valleys. By analyzing samples from various sites in the Dry Valleys, the team behind the new study compared microorganisms from the wider region with those at Blood Falls to determine if Blood Falls has a distinct microbial assemblage potentially left over from ancient conditions.

The researchers found that the crimson brine and associated red-tinted sediments at Blood Falls shared a higher proportion of eukaryotes with nearby oceanic samples than other sites in the Dry Valleys did. Whereas Blood Falls had a little over 9% of its eukaryotes in common with the ocean, the Dry Valleys showed only about 1% similarity, according to the study. The remaining eukaryotes and most of the prokaryotes identified in the paper had freshwater and terrestrial origins.

The results also showed that the air near Blood Falls contained only a tiny proportion of marine microorganisms, suggesting that present-day winds can't fully explain the microbial composition of Blood Falls, the researchers wrote.

Therefore, an ancient seawater origin is the most likely explanation for the microorganisms found at Blood Falls today, the team concluded. Winds may have played a role in shaping the community in the past, but now, their influence is probably insignificant, the team added.

The brine that feeds Blood Falls may have become entrapped more than 1 million years ago, during a warm period with higher sea levels and less ice cover than there is now, previous estimates suggested. However, further work, including more comprehensive genetic profiling and mapping of microorganisms, is needed to pinpoint when Taylor Valley's glacier grew to cover the brine, the researchers wrote.

Antarctica quiz: Test your knowledge on Earth's frozen continent

While millions around the world grappled with extreme heat this month, a research station in Antarctica recorded Earth's coldest temperature since 2012.

The high-altitude research station, named Concordia, logged a low of minus 119.4 degrees Fahrenheit (minus 84.1 degrees Celsius) on July 18, according to data from the station.

Concordia is located in the interior of the Antarctic continent, which is currently in the dead of winter with no sunlight. Temperatures at the station regularly fall below minus 112 F (minus 80 C) this time of year ‪—‬ so the new reading isn't unprecedented, but it's still significant.

"Even here, where extreme cold is expected, temperatures below minus 84 C are remarkable and highlight how variable Antarctic weather can still be," Gabriele Carugati, the station leader at Concordia for Italy's National Antarctic Research Program (PNRA), told Live Science over a video call from the station.

The French Polar Institute Paul-Émile Victor, which runs Concordia with the PNRA, sent Live Science raw data from July 18, which showed the temperature dropping to minus 84.1 C twice, at 6:25 a.m. and 6:34 a.m. local time.

The extreme chill at Concordia stands in sharp contrast to the sweltering heat that many countries are currently experiencing. North America and Europe have been battling heat waves this summer, with Western Europe recording the hottest June on record. Meanwhile, wildfires are raging in Canada, the U.S., France, Spain and other countries.

Globally, average temperatures are going up as humans pump more heat-trapping greenhouse gases into the atmosphere. However, Earth's weather systems are complex, and climate change doesn't mean that everywhere gets hotter all of the time.

"Climate change describes the long-term global trends, while individual weather events can still [bring] exceptional cold," Carugati said. "Antarctica is influenced by complex atmospheric processes, so an extreme low temperature at one location does not contradict the broader picture of global warming."

"Astronauts of ice"

Concordia is considered the most remote and extreme research station in the world. Built on top of a 10,800-foot-thick (3,300 meters) ice cap, the station is used for a variety of purposes, including seismic observations, astronomy and the modeling of Earth's past climates, according to the French Polar Institute Paul-Émile Victor.

"Concordia is a special place because it sits at over 3,200 meters [10,500 feet] above sea level on the Antarctic Plateau, and more than 1,000 kilometers [600 miles] from the coast," Carugati said. "During winter, there is no sunlight for months, the atmosphere is extremely dry and stable, and under clear skies, heat continuously escapes to space because there are no clouds, allowing temperatures to fall to extraordinary levels."

Concordia's environment is so harsh and isolated that the station is also used to improve our understanding of the physical, mental and social challenges astronauts experience in space. Carugati noted that the only person at the station who is not researching the environment is a European Space Agency biomedical doctor, who is studying the researchers who work there, nicknamed "astronauts of ice."

Planes can't fly to Concordia once winter sets in, and it's around 370 miles (600 kilometers) from the nearest research station. That technically makes crews more isolated than astronauts on the International Space Station, which orbits about 250 miles (400 km) above Earth, according to the European Space Agency.

What is the coldest temperature ever recorded?

The coldest temperature ever recorded at Concordia was minus 120.5 F (minus 84.7 C), logged in the winter of 2010, according to the Italian Antarctic Meteo-Climatological Observatory. However, another high-altitude research station in East Antarctica has the all-time record for the coldest temperature ever recorded on Earth. Russia's Vostok weather station, the nearest station to Concordia, recorded a temp of minus 128.6 F (minus 89.2 C) in July 1983, according to the World Meteorological Organization.

Satellite data suggests that temperatures can drop as low as minus 144 F (98 C) in East Antarctica, according to a 2018 study published in the journal Geophysical Research Letters. However, even though Antarctica is the coldest and driest continent, it's not immune to global warming.

Major glaciers and the ice sheet they support are at risk in West Antarctica, with the Antarctic Peninsula — which extends out of the western side of the continent — experiencing the most rapid warming. A study published in February in the journal Frontiers in Environmental Science found that decisions made on greenhouse gas emissions today will determine how much the peninsula will change in the coming centuries, with sea ice, ice shelves and glaciers, along with the penguins that live on them, at risk of disappearing.

Concordia sits on the largest ice sheet on Earth. This sheet in East Antarctica is more stable than the smaller sheet of West Antarctica, but it is still vulnerable to rising temperatures. An unprecedented Antarctic winter heat wave in March 2024 saw temperatures near Concordia rise to a record high of 15.1 F (minus 9.4 C) ‪—‬ about 32 F (18 C) warmer than the previous March maximum. This East Antarctic heat wave was amplified by global warming, according to a study published in April in the journal npj Climate and Atmospheric Science.

Earth recently entered an El Niño, the warm phase of a multiyear natural climate pattern, which could bring unprecedented temperature extremes to an already-warming world. Carbon Brief, a U.K. based outlet that reports on climate news and policy, has predicted that 2026 is likely to be the second-warmest year on record, behind 2024, with the intensifying El Niño increasing the likelihood that 2027 will be the warmest year ever recorded.

For now, at Concordia, the researchers are continuing their work in the blistering cold of Antarctica's winter. Carugati noted that the latest extreme-temperature data will inform forecasts and long-term climate monitoring.

"Extreme observations like this help scientists better understand atmospheric processes and improve the climate models," he said.

A colossal chunk of sea ice roughly the size of Texas is missing from the west coast of Antarctica, and scientists fear it might never form again.

Antarctica is currently in winter, which runs from March to October on the southernmost continent. During the winter months, floating sea ice surrounding the continent typically grows, driving currents that regulate Earth's climate. But this year, there's a notable ice gap over the Bellingshausen Sea, on the western side of the Antarctic Peninsula.

Satellite observations have revealed that around 250,000 square miles (650,000 square kilometers) of sea ice hasn't formed yet, compared with the average amount of sea ice between 1991 and 2020, The Guardian reported last week. For comparison, the ice gap covers an area slightly larger than France or nearly the size of Texas.

Will Hobbs, a sea ice-ocean interaction scientist at the University of Tasmania, told The Guardian that he was "concerned" by the lack of sea ice and that it was "depressing." Hobbs noted that this year represents the third time in four years that the region's sea has been very low.

"I don't think we will see sea ice there any more," he said. "It's done."

Researchers still have a lot to learn about sea ice changes in Antarctica. Hobbs said that the sea ice loss was likely linked to changes in the ocean and that scientists are trying to determine whether global warming was a factor.

Sea ice has declined much more slowly in Antarctica than in the Arctic. But in recent years, scientists have been witnessing an astonishing change in the sea ice extent. One record low in 2016 was followed by another in 2022 and then a third in 2023.

Edward Doddridge, a physical oceanographer at the Institute for Marine and Antarctic Studies in Australia, told ABC News (Australia) that he was no longer surprised by sea ice loss.

"It's not good news, but it has become a pattern that we're expecting now," Doddridge said. "A warming world is going to have less sea ice."

The diminished winter sea ice is likely to have a variety of knock-on effects. For example, this area of sea ice normally provides important habitat for animals like krill and penguins. Sea ice also plays an important role in regulating the climate, including by driving key ocean currents, insulating the ocean from the sun, and protecting ice shelves at the mouths of glaciers.

Down the coast from the missing sea ice, researchers have warned that a key ice shelf is about to disintegrate from Antarctica's Thwaites Glacier — nicknamed the "Doomsday Glacier" because its collapse could raise sea levels by 2.1 feet (65 centimeters) in the coming centuries, flooding coastal communities worldwide. The ice shelf helps protect the mouth of the glacier by acting as a buttress, thereby restraining the flow of ice from the glacier into the sea.

Thwaites Glacier has been melting rapidly since the 1980s, which is part of a wider concern for the West Antarctic Ice Sheet that it helps to support. The collapse of such an ice sheet is considered one of the major environmental tipping points, or "points of no return," that humanity must avoid in the fight to rein in climate change.