Quantcast

Melting Antarctic Glacier Unstoppable, Global Sea Level Could Rise by 4 Feet

Climate

A rapidly melting section of the West Antarctic Ice Sheet appears to be in irreversible decline, with nothing to stop the entire glacial basin from disappearing into the sea, according to researchers at University of California Irvine and NASA.

The new study presents multiple lines of evidence—incorporating 40 years of observations that six massive glaciers in the Amundsen Sea sector “have passed the point of no return,” according to glaciologist Eric Rignot, a University of California Irvine Earth system science professor who is also with NASA’s Jet Propulsion Laboratory. The new study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

West Antarctica's Thwaites Glacier is one of six believed to be on an irreversible path to melting away. Photo credit: NASA

These glaciers already contribute significantly to sea level rise, releasing as much ice into the ocean each year as the entire Greenland Ice Sheet does. They contain enough ice to boost the global sea level by four feet (1.2 meters) and are melting faster than most scientists had expected. Rignot said the findings will require that current predictions of sea level rise be revised upward.

“This sector will be a major contributor to sea level rise in the decades and centuries to come,” Rignot said. “A conservative estimate is that it could take several centuries for all of the ice to flow into the sea.”

Three Lines of Evidence

Three major lines of evidence point to the glaciers’ eventual demise: changes in their flow speeds, how much of each glacier floats on seawater, and the slope and depth below sea level of the terrain they’re flowing over. In a paper published last month, the research group showed that the speed at which the glaciers are moving has accelerated steadily for four decades, increasing the amount of ice draining from them by 77 percent from 1973 to 2013. This new study focuses on the other two lines of evidence.

The West Antarctic glaciers flow out from land over the ocean, with their front edges afloat. The point at which they lose contact with land is called the grounding line. Virtually all glacial melting occurs on the undersides of their floating sections—beyond the grounding line.

Just as a boat that’s run aground can float again if its cargo is unloaded, a glacier can float over an area where it used to be grounded if it becomes lighter, which it does by melting or by stretching out and thinning. The Antarctic glaciers studied by Rignot’s group have shrunk so much that they’re now floating above places where they used to sit solidly on land, which means the grounding lines are retreating inland.

They’re “buried under a thousand or more meters of ice, so it’s incredibly challenging for a human observer on the ice sheet surface to figure out exactly where the transition is,” Rignot said. “This analysis is best done via satellite techniques.”

The team used radar observations from the European Remote Sensing satellites (ERS-1 and ERS-2) between 1992 and 2011 to map the grounding lines’ inland creep. The satellites employ a method called radar interferometry that enables scientists to measure very precisely— within a quarter of an inch—how Earth’s surface is moving. Glaciers shift horizontally as they flow downstream, but their floating portions also rise and fall with changes in the tides. Rignot and his group mapped how far inland these vertical motions extend to locate the grounding lines.

Vicious Cycle

The accelerating flow speeds and retreating grounding lines reinforce each other in a recurring loop. As glaciers move faster, they stretch out and thin, which decreases their weight and lifts them farther off the bedrock. As the grounding line retreats and more of the glacier becomes waterborne, there’s less resistance underneath, so the flow accelerates, and so on—with each action intensifying the next.

Slowing or stopping these changes requires “pinning points”—bumps or hills rising from the glacier bed that snag the ice from below. To locate them, researchers produced a more accurate map of bed elevation that combines ice velocity data from ERS-1 and ERS-2 and ice thickness data from NASA’s Operation IceBridge mission and other airborne campaigns. The results confirmed that just one pinning point remains upstream of the current grounding lines. Only Haynes Glacier has major bedrock obstructions upstream, but it drains a small sector and is retreating as rapidly as the other glaciers.

Bed topography is another key to the fate of the ice in this basin. All the glacier beds slope deeper below sea level as they extend inland. As they retreat, they cannot escape the ocean’s reach, and the relatively warm water melts them even more rapidly.

The accelerating flow rates, lack of pinning points and sloping bedrock all point to one conclusion, Rignot said:

“The collapse of this sector of West Antarctica appears to be unstoppable. The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating parts of the glaciers. At this point, the end appears to be inevitable.”

--------

YOU MIGHT ALSO LIKE

Will White House Climate Report Spark Action on Global Warming?

Major Antarctic Glacier Melting Irreversibly, Reaching Tipping Point

Researchers Discover Arctic Warmer Than Anytime in Last 44,000 Years 

--------

EcoWatch Daily Newsletter

A verdant and productive urban garden in Havana. Susanne Bollinger / Wikimedia Commons

By Paul Brown

When countries run short of food, they need to find solutions fast, and one answer can be urban farming.

Read More Show Less
Trevor Noah appears on set during a taping of "The Daily Show with Trevor Noah" in New York on Nov. 26, 2018. The Daily Show With Trevor Noah / YouTube screenshot

By Lakshmi Magon

This year, three studies showed that humor is useful for engaging the public about climate change. The studies, published in The Journal of Science Communication, Comedy Studies and Science Communication, added to the growing wave of scientists, entertainers and politicians who agree.

Read More Show Less
Sponsored
rhodesj / Flickr / CC BY 2.0

Cities around the country are considering following the lead of Berkeley, California, which became the first city to ban the installation of natural gas lines in new homes this summer.

Read More Show Less
Rebecca Burgess came up with the idea of a fibersheds project to develop an eco-friendly, locally sourced wardrobe. Nicolás Boullosa / CC BY 2.0

By Tara Lohan

If I were to open my refrigerator, the origins of most of the food wouldn't be too much of a mystery — the milk, cheese and produce all come from relatively nearby farms. I can tell from the labels on other packaged goods if they're fair trade, non-GMO or organic.

Read More Show Less
A television crew reports on Hurricane Dorian while waves crash against the Banana River sea wall. Paul Hennessy / SOPA Images / LightRocket / Getty Images

By Mark Hertsgaard and Kyle Pope

Some good news, for a change, about climate change: When hundreds of newsrooms focus their attention on the climate crisis, all at the same time, the public conversation about the problem gets better: more prominent, more informative, more urgent.

Read More Show Less
Sponsored
U.S. Senators Chris Coons (D-Del.) and Mike Braun (R-Ind.) met with Bill Gates on Nov. 7 to discuss climate change and ways to address the challenge. Senator Chris Coons

The U.S. Senate's bipartisan climate caucus started with just two members, a Republican from Indiana and a Democrat from Delaware. Now it's up to eight members after two Democrats, one Independent and three more Republicans joined the caucus last week, as The Hill reported.

Read More Show Less
EPA scientists survey aquatic life in Newport, Oregon. U.S. Environmental Protection Agency

The U.S. Environmental Protection Agency (EPA) is proposing to significantly limit the use of science in agency rulemaking around public health, the The New York Times reports.

Read More Show Less
A timelapse video shows synthetic material and baby fish collected from a plankton sample from a surface slick taken off Hawaii's coast. Honolulu Star-Advertiser / YouTube screenshot

A team of researchers led by the National Oceanic and Atmospheric Administration didn't intend to study plastic pollution when they towed a tiny mesh net through the waters off Hawaii's West Coast. Instead, they wanted to learn more about the habits of larval fish.

Read More Show Less