Looking at Antarctica in the summer, time seems to have frozen. The Antarctic midnight sun appears to hover in place, never setting below the horizon for several weeks from November to January.
But Antarctic eternity is an illusion. Just a decade ago, on summer nights on the coast, the sun would move gently across the ocean, coating the ice floes with a golden glow.
Today, however, much of the sea ice is no longer visible. Scientists are increasingly concerned it may never return.
“Antarctica It feels remote, but the sea ice out there is important to all of us,” Ella Gilbert, a polar climate scientist at the British Antarctic Survey told LiveScience. “This is a very important part of our climate system.”
Until recently, Antarctic sea ice fluctuated between relatively stable summer minimums and winter maximums. But after hitting record lows in 2016, things started to change.Two all-time lows soon followed, including a record low in February 2023 of just 737,000 square miles (1.91 million square kilometers).
Winter began that March, and scientists hoped the ice sheets would rebound. But what happened surprised them: Antarctic ice experienced six months of record lows. During the peak of winter in July, the continent was missing a chunk of ice larger than Western Europe.
“We all agree that the lowest is the worst; that’s 2023, not 2070,” Arian PritschAntarctic climate researcher at Australia’s Monash University told Live Science. “So when winter came, we couldn’t believe it.”
Now, in 2024, sea ice extent has reached a near-record low: only 766,400 square miles (1.985 million square kilometers) February 20th.
related: ‘Everything beats expectations in 2023’: Antarctic sea ice falls to disturbing lows for third year in a row
A profound “regime shift” has occurred in the Antarctic region, and climate scientists are racing to understand what happens next.
“When you push any part of the climate system, it has ripple effects that are felt around the world — not necessarily immediately, but years later,” Gilbert said. “So by getting more and more Push the system harder and we’ll make these ripples bigger and bigger, and eventually we’ll all feel them.”
The heartbeat of the ocean
As Antarctica’s summer turns into winter, sea ice expands from a minimum of about 1 million square miles (3 million square kilometers) to 7 million square miles (18 million square kilometers), covering 4% of the Earth’s surface in an irregular porcelain shape. White tiles.
Most sea ice grows in open water on floating ice shelves that ring the continent during winter’s weeks-long polar night. Struck by strong winds from inland, seawater holes or polynyas in floating ice shelves freeze and are sprinkled with snow, forming ice layers one by one.
Coastal ice mosaics have many uses. First, this sea ice moat continuously warms the water in the continent’s increasingly unstable land ice, thus protecting its hanging glaciers. The surface of sea ice also reflects some of the solar energy back into space, a process called the albedo effect.
These floating platforms also play a key role in the Antarctic ecosystem, providing habitat for creatures such as penguins and krill. The krill feed on photosynthetic algae growing around the platform, and their poop locks in carbon dioxide, which then falls to the seafloor.
Sea ice also contributes to the conveyor belt that drives ocean circulation. As sea ice melts, cold water pouring down from the continental shelf pushes deep water further downward, forming the Circumpolar Current, which drives all the world’s ocean currents. Actually, 40% of the world’s oceans Its origins can be traced to the Antarctic coastline, making it crucial for regulating regional climate around the world.
It seems that the rhythmic expansion and contraction of the ice sheet is like heartbeatpushing nutrients, oxygen and heat around the world and sucking carbon dioxide into the deep ocean, About 30% of carbon emissions are trapped there For hundreds of years.
For most of recorded history, the “heartbeat” of the ocean and its impact on the carbon cycle and ocean circulation have been fairly stable. But then it skipped a beat.
New record
Satellite records chart Earth’s sea ice every year, measuring sea ice fluctuations at the poles since 1979.
The future of the Arctic has always been simple and bleak: Ice coverage continues to decline Exceed 12% every ten years.
However, on the other side of the world, Antarctica appears to be beating the odds. Until 2015, Antarctica’s ice extent not only remained stable but also increased slightly, and in fact reached an all-time high in 2014. A chance event or an ominous fundamental shift.
“What has happened over the past seven years is likely to continue,” Martin Siegert, a glaciologist who leads surveys of Antarctic sea ice decline, told Live Science.
A key factor in the rapid melting of the Arctic is a process called surface albedo feedback. When sea ice melts, it exposes darker waters that absorb more sunlight.This vicious reversal of the albedo effect has transformed the Arctic from a refrigerator into a radiator, and now it’s warming Four times faster than the rest of the world.
“If we started losing sea ice every year, and the same process happened in Antarctica as in the Arctic, Antarctica would warm at an accelerated rate. That would be a disaster for the planet,” Siegert said.
Before 2016, scientists held out faint hope that Antarctica’s complex system could temporarily stabilize global climate. Now, that hope has been dashed.
In a September 2023 paper, Prich and her colleague Edward Doddridge found the first clue that changes in the Antarctic sea ice system were more than just an aberration: In 2015, the Southern Ocean Warming begins at depths of 330 to 660 ft (100 ft).
related: ‘Unprecedented, ‘stunned’, ‘unbelievable’: Changing Antarctic sea ice could have huge impact, says climate scientist Edward Doddridge
Because sea ice loss tends to occur in areas of highly warmed oceans, which changes the way the atmosphere and ocean interact to form ice, the Antarctic system enters a new state. Prich said it was this change that contributed to last year’s record lows.
The new Antarctica behaves differently. Before the apparent shift, there was no connection between summer minimum and winter maximum sea ice. Now, the two are closely linked.
what’s next
The direct impacts of Antarctic sea ice loss are already being felt.For example, the 2022 decline resulted in Massive death of thousands of emperor penguin chicks In West Antarctica, scientists expect to see more deaths starting in 2023. Biggest heat wave on recordtemperatures were 72 degrees Fahrenheit (40 degrees Celsius) above normal.
related: Hundreds of Emperor Penguin chicks fall from 50ft cliff in unprecedented footage
Additionally, deep ocean currents around Antarctica have 30% slowdown since 1990sexpected to slow down Increase by another 40% by 2050.
Although the reverse albedo feedback causes an accelerated response, scientists are careful not to call the decline of Antarctic sea ice an irreversible tipping point.
“If the weather is a little colder, [sea ice] It could freeze again,” Prich said.
The bigger concern, however, is that a lack of sea ice could trigger other lasting tipping points in the region, she noted.
“In the absence of sea ice, waves break ice shelves faster than they would otherwise,” Prich said. “Once ice shelves break, the land ice they support can slide into the ocean.”
If the West Antarctic ice sheet alone broke off and melted into the sea, global sea levels would rise by about 11 feet (3.4 m).
A weakening of Antarctic-driven ocean circulation could also accelerate the collapse of key ocean currents, such as the Atlantic Meridional Overturning Circulation (AMOC), which helps maintain the temperate climate of the Northern Hemisphere.
recent, Worrying research Point out that AMOC’s strength is declining.If the ocean currents weaken as before during the last ice ageFor example, temperatures in Europe and North America could drop by as much as 9 degrees Fahrenheit (5 degrees Celsius) within a decade.
The timing and impact of these secondary tipping points have become crucial issues. However, despite agreement on the significant impacts of climate change, Antarctica’s complexity, lack of historical data and difficulties in obtaining funding to collect data make accurate predictions challenging.
“Antarctica is difficult. It’s hard to model; it’s hard to measure. It’s hard to even get there,” caroline holmespolar researchers at the British Antarctic Survey told Live Science. “But there’s a lot of research momentum right now that says we need to do more.”
In the meantime, the obvious prescription for our troubled planetary system still applies: urgent and deep cuts in global carbon dioxide emissions, Siegert said.
“The only way out is decarbonization, and decarbonizing as quickly as possible means we don’t see the worst outcomes,” Siegert said.
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