The Pine Island Glacier on the coast of West Antarctica is a case in point. A massive iceberg roughly 225 square miles in size — or in more familiar terms, 10 times the size of Manhattan — broke off in July 2015. Scientists subsequently spotted cracks in the glacier on a November 2016 flyover. And in January, another iceberg cleaved off the glacier.
The ocean under Pine Island Glacier’s ice shelf has warmed about 1°F since the 1990s. That’s causing the ice shelf to melt and pushing the grounding line — the point where the ice begins to float — back toward land, creating further instability.
Thwaites Glacier on the edge of West Antarctica is one of the planet’s fastest-moving glaciers. Research shows that it is sliding unstoppably into the ocean, mainly due to warmer seawater lapping at its underside.
Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.
Sea ice off Antarctica and in the Arctic is at record lows for this time of year after declining by twice the size of Alaska in a sign of rising global temperatures, climate scientists say. “There are some really crazy things going on,” said Mark Serreze, director of the U.S. National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, saying temperatures in parts of the Arctic were 20 degrees Celsius (36°F) above normal some days in November. Worldwide, this year is on track to be the warmest on record. Combined, the extent of polar sea ice on Dec. 4 was about 3.84 million square kilometers (1.48 million square miles) below the 1981-2010 average, according to NSIDC satellite measurements. That is roughly the size of India, or two Alaskas.
For most of the latter half of the 20th century, the Antarctic Peninsula was one of the fastest-warming places on the planet, with serious repercussions for the local environment, including the spectacular disintegration of a millennia-old ice shelf, and global sea level rise.
But a new study detailed Thursday in the journal Nature suggests temperatures on the peninsula have dropped slightly since the late 1990s. This relative cooling is partly driven by the recovery of the ozone hole, and is, along with the warming that preceded it, within the realm of the wild shifts in climate the region has naturally experienced in the past, they found.
The cooling is relatively minor — less than 2 degrees F (1 degree C) since the 1990s — and it doesn’t negate the background warming that is happening because of the steady rise of heat-trapping greenhouse gases in the Earth’s atmosphere, the researchers said. It is simply masking it for the time being. Eventually, human-driven warming will overwhelm the influence of the ozone hole recovery and natural climate drivers, and temperatures will once again rise.
Up and down
The Antarctic Peninsula is the arm of land that juts up from the continent. Between 1951 and 2000, the temperature at one weather station on its west coast rose by about 5 degrees F (2.8 degrees C), compared to a little more than 1 degree F (0.5 degrees C) globally.
That warming was accompanied by significant decreases in sea ice, changes to plant and animal communities, and the melt of land-bound glaciers and the floating ice shelves that buttress them.
In 2002, the Larsen B ice shelf spectacularly collapsed, stunning Antarctic researchers. A 2014 study pointed to the warm air that bathed the peninsula in the preceding summers as the precipitating cause of the ice shelf’s demise.
But since the 1990s, the average temperature of the peninsula has declined by 0.9°F (0.5°C) per decade, Turner and his colleagues found when they looked at weather station data. That is about the same rate that it had warmed in the previous five decades.
There had been signs that the warming had abated, such as a slowing of the expansion of plants that linked the higher temperatures, and a smaller proportion of glaciers in retreat. Turner and his team wanted to know what was causing the relative downturn.
“Nowhere on Earth does climate change for a single reason,” he said.
The researchers found that changes in regional wind patterns — from warm-inducing westerlies to cold-bringing easterlies — were linked to both the warming and cooling periods the peninsula has undergone.
The development and then recovery of the ozone hole was a key driver, as it helped to alter those winds, as did the prevailing climate patterns in the tropical Pacific Ocean.
“The ozone hole really had a big impact, especially in the summer,” Turner said.
The period of warming was due to some combination of the ozone hole, greenhouse warming, and a tendency toward El Niño-like conditions in the Pacific, all favoring warmer westerlies. The cooling period has happened as the ozone hole has begun to heal and the Pacific Ocean favored La Niña-like conditions, ushering in more easterlies. (Those easterly winds also blew sea ice toward the peninsula and helped to reinforce the cooling, as the ice blocked the transfer of heat from the ocean to the atmosphere.)
“This is an excellent study by some of the international leaders in Antarctic climate — what it does is provide a climate context for a trend that’s been reported in a couple of ways previously,” Ted Scambos, a glaciologist at the National Snow & Ice Data Center in Boulder, Colo., said in an email. Scambos was not involved in the study.
Warming will win out
To put the warming and cooling periods into context, the team included analyses of ice core records. These cylinders of ice drilled from Antarctic glaciers can reveal temperature patterns and showed that episodes like these had occurred in the past as the result of natural variations in climate. The warming period, while unusual, wasn’t unprecedented. Nor is the cooling period.
That doesn’t mean that greenhouse gas-driven warming isn’t playing a role now, either on the peninsula or on Antarctica as a whole (of which the peninsula only makes up 1 percent). Instead, it means that the large ups and downs driven by the ozone hole and natural variability are overwhelming the long-term warming signal for the time being.
If emissions of carbon dioxide and other gases continue, that signal will eventually emerge, likely sometime in the next two to three decades, Turner said. Then the impacts — from disrupting the peninsula’s resident Adélie penguins to causing further ice melt and sea level rise — will resume.
“The effect of this cooling/flattening of the warming trend in the northern Peninsula is to put the region into a giant holding pattern,” Scambos said, “hanging right at the tipping point of further massive retreat and glacier speed-up.”
Carbon dioxide has been steadily rising since the start of the Industrial Revolution, setting a new high year after year. There’s a notable new entry to the record books. The last station on Earth without a 400 parts per million (ppm) reading has reached it. In the remote reaches of Antarctica, the South Pole Observatory carbon dioxide observing station cleared 400 ppm on May 23, according to an announcement from the National Oceanic and Atmospheric Administration on Wednesday. That’s the first time it’s passed that level in 4 million years
An estimated 150,000 Adelie penguins living in Antarctica have died after an iceberg the size of Rome became grounded near their colony, forcing them to trek 60km to the sea for food.
The penguins of Cape Denison in Commonwealth Bay used to live close to a large body of open water. However, in 2010 a colossal iceberg measuring 2,900 square kilometres became trapped in the bay, rendering the colony effectively landlocked.
Penguins seeking food must now waddle 60km to the coast to fish. Over the years, the arduous journey has had a devastating effect on the size of the colony.
Since 2011 the colony of 160,000 penguins has shrunk to just 10,000, according to research carried out by the Climate Change Research Centre at Australia’s University of New South Wales. Scientists predict the colony will be gone in 20 years unless the sea ice breaks up or the giant iceberg, dubbed B09B, is dislodged.
Penguins have been recorded in the area for more than 100 years. But the outlook for the penguins remaining at Cape Denison is dire.
“The arrival of iceberg B09B in Commonwealth Bay, East Antarctica, and subsequent fast ice expansion has dramatically increased the distance Adélie penguins breeding at Cape Denison must travel in search of food,” said the researchers in an article in Antarctic Science.
“The Cape Denison population could be extirpated within 20 years unless B09B relocates or the now perennial fast ice within the bay breaks out”
“This has provided a natural experiment to investigate the impact of iceberg stranding events and sea ice expansion along the East Antarctic coast.”
In contrast, a colony located just 8km from the coast of Commonwealth Bay is thriving, the researchers said.
The iceberg had apparently been floating close to the coast for 20 years before crashing into a glacier and becoming stuck.
January 1995 marked a seminal moment in modern Antarctic history, with the crumbling of the Larsen A ice shelf, a floating plain of ice fed by glaciers on the Antarctic Peninsula. Less than a decade later, its southern neighbor, the Larsen B ice shelf, disintegrated, stunning polar scientists.
After the spectacular collapses of Larsen A and B, scientists began keeping a close watch on the next ice shelf to the south, the Larsen C, which has shown some worrying signs of thinning. At about the area of Scotland, it is five times larger than the Larsen B (itself five times as large as the Larsen A), “so when Larsen C goes, it’s going to be a really big event,” Paul Holland, a researcher with the British Antarctic Survey, said.
The failure of the Larsen C would mean that Antarctica’s contribution to sea-level rise would increase, further imperiling Earth’s built-up coastlines.
The loss of the Larsen A and B ice shelves caused the glaciers behind them to speed their flow to the sea, contributing to the rise of global sea levels that are already threatening the more than 1 billion people who live along coastlines. Since the beginning of the 20th century, global sea levels have risen by 8 inches, making storm surges during events like Hurricane Sandy higher and more destructive than they once were and causing more regular minor floods in coastal areas.
The most recent Intergovernmental Panel on Climate Change report estimates global sea levels could rise by between 10 and 39 inches by 2100. The IPCC estimates that Antarctica’s current contribution to that rise is about one one-hundredth of an inch a year.
One key question Antarctic scientists have been trying to answer is what exactly is happening to the Larsen C: Are warm waters melting it from below, or is warming air melting it from above?
A new study from Holland and his colleagues, detailed in the journal The Cryosphere, suggests it could be both.
Lots of ice shelves all around Antarctica have been shrinking in recent years, and doing so at an increasing rate, as recent research has shown. Most of these are being eaten away from below, as warm ocean waters invade and lap away at the ice. Air temperatures, while warming, are still too cold to cause much surface melt across much of the continent.
But on the Antarctic Peninsula — the arm that stretches northward from the continent toward South America — rising air temperatures are impacting the ice. The region is a global hotspot for warming, with temperatures that have risen by about 5 degrees F in the past 50 years, while the globe as a whole has warmed by about 1.3 degrees F.
A study published last year pointed the finger at this warming as the reason for the Larsen B collapse, arguing that the elevated temperatures caused excessive surface melt that led to significant cracks in the ice.
When it comes to the Larsen C shelf, both warming air and melting ice are potential culprits. The surface of the ice shelf has been getting lower and lower in recent decades, but it was unclear what the source of that lowering was. It could be that the layer of compacted snow at the surface, called firn, was melting and compacting further still, or it could be that ice from the bottom of the shelf was melting, causing the height of the glacier to adjust. Or it could be some combination of the two.
That’s what Holland and his colleagues set out to tease apart with their research. To do this, they stitched together data from eight different radar surveys, some conducted by airplane and others done by dragging the equipment across the ice. The radar can penetrate the layers of ice to show how thick both the firn layer and the shelf as a whole are.
What they found was that the ice shelf was indeed losing ice, and that the firn layer was shrinking.
“The fact that it’s sort of being attacked by both does make it unique,” Holland said.
What exactly is causing the ice loss and firn compaction is still not fully known. It’s possible the firn is melting and compacting because of warmer air, or it could simply be that less snow is falling to build it up. For the ice loss, which is the larger force affecting the shelf, it could be that the ocean waters are melting the ice, or that the flow of the ice is changing.
“There’s all kinds of wacky possibilities,” Holland said. “It’s really tough to figure out what it is.”
Ted Scambos, a researcher with the U.S. National Snow and Ice Data Center in Boulder, Colo., said that the new study did a good job of separating the potential influences on the ice shelf and backs up what others have long suspected was happening in the region. Scambos was not involved with the study.
The one-two punch to the Larsen C makes the ice shelf more vulnerable, particularly with some other worrying signs. The biggest threats to the ice shelf’s stability, Holland thinks, come from indications it could unpin itself from an island that helps slow its flow, as well as a rift that has formed across the ice. If that rift reaches more vulnerable parts of the ice sheet, it could seriously destabilize it.
“That’s a thing we need to keep an eye on,” Holland said.