Antarctica is About to Lose a 2,000 Square Mile Chunk of Ice — And it Could Mean the End of the Larsen C Ice Shelf

It’s happened before. Ice shelves on the northern Antarctic Peninsula released large chunks of ice into the Southern Ocean as the world warmed up. They developed a concave shape which became unstable. Then they collapsed.

The ultimate collapse of Larsen A occurred in 1995. In 2002, further up the Antarctic Peninsula, the larger Larsen B Ice Shelf succumbed to the same fate. And it is thought that such losses haven’t happened to this section of Antarctica in at least 11,000 years and possibly as long ago as 100,000 years.

(NASA’s Jet Propulsion Laboratory provides this narrative describing the collapse of the Larsen B Ice Shelf in 2002. Video source: JPL.)

But in the present world, one where human fossil fuel emissions have forced global temperatures above 1 C hotter than 1880s averages, the stability of many of the great great ice shelves is now endangered.

Larsen C Ice Shelf to Calve 2,000 Square Mile Ice Berg

Today, a huge rift has nearly bisected a large frontal section of the Larsen C Ice shelf — an ice system many times the size of its now deceased companions Larsen A and Larsen B. And during December — a period when Antarctica was warming into Austral Summer — this massive crack grew by 18 kilometers.

When, and not if, the crack reaches the ocean, a 2,000 square mile ice berg will float away from Larsen C. It will be one of the largest ice bergs ever to form in human memory. One the size of the state of Delaware. It will tower hundreds of feet above the ocean surface. And it will last for years before ultimately melting.

larsen-c-ice-rift-length-and-width

(The Larsen C is rift grew considerably — both lengthening and widening during December of 2016. It was an indication that a massive ice berg was about to break off. Image source: MIDAS.)

This event will change the geography of our world. And for this alteration alone, it has great consequence. But, as Chris Mooney notes in this excellent Washington Post article on the subject, it’s what happens afterward that really counts.

Event Could Presage Total Collapse

Of concern is the fact that once this massive ice berg calves off of Larsen C, the great ice sheet may become unstable. It will take on a concave form. This form will make it more vulnerable to further melt by warming waters running in toward the shelf. Furthermore, the large ice berg will take a chunk of Larsen C’s compressive arch with it. Such a compressive arch — like the arch of a flying buttress — helps to bear the weight of the shelf and keep it from smashing into thousands of tiny pieces. If too much of the arc is lost, the shelf can’t survive for long.

larsen-c-ice-rift-midas

(Researchers at The MIDAS Project have projected that a 2,000 square mile section of the Larsen C Ice Shelf is about to break off. This section represents 10 percent of the Larsen C system. Its loss risks destabilization of the entire ice shelf. If Larsen C does disintegrate, it will release glaciers capable of increasing global sea level by another 4 inches. Image source: MIDAS.)

Glaciologist Eric Rignot notes in The Washington Post:

“We studied the current rift in the past few years, it has been progressing rather ‘normally,’ the recent acceleration in the rift progression is ‘expected’ in my opinion. The consequences on the rest of the ice shelf are not clear at this point. If the calving continues and goes past the compressive arch … then the ice shelf will break up.”

Scientists are currently divided over the issue of whether or not Larsen C’s near-term demise is imminent. However, the loss of such a massive ice berg from Larsen C, the present human-forced warming of the Antarctic land and ocean environment, and the presently observed thinning of the ice shelf all point toward a rising risk of destabilization or disintegration.

As with most things geological, you can’t really say that such an event is certain until after the fact. But as for Larsen C’s prospects of long term survival, things aren’t looking too great at the moment.

Links/Credits

The MIDAS Project

Antarctica is Set to Lose an Enormous Piece of Ice

An Ice Berg the Size of Delaware is About to Break off From Antarctica

NASA’s Jet Propulsion Laboratory

Warm, Storm-Force Winds Blowing From the Equator Flip West Antarctic Winter to Summer

In a record-hot world, there’s a lot of lower-latitude heat just waiting for a weakness in the increasingly feeble Jet Stream to make a big poleward rush. Such was the case today as an intense wave of warmth exploded up from the Equatorial region and began to spread summertime temperatures over sections of West Antarctica — technically still in the grips of the Southern Hemisphere’s winter season.

image

(A surge of heat breaks over West Antarctica on September 2nd, 2016, pushing air temperatures over vulnerable coastal glaciers and ice shelves near or above the melting point [0 degrees Celsius]. Image source: Earth Nullschool.)

The warm winds began their southward turn about a thousand miles west of coastal South American and along the 20 degrees south latitude line. Tapping hot, tropical air, the winds then ran over hundreds of miles of open ocean — following the arch of a bulging ridge in the Jet Stream. These winds then gathered, howling through the Southern Ocean with storm force gusts of 50 to 65 mph before delivering their payload of abnormal warmth to West Antarctica.

Larsen C Ice Shelf Experiencing Above-Freezing Temperatures in Winter

Along the coast of Ellsworth Land, temperatures have risen to near the thawing point (0 degrees C), in winter, in a region that typically sees -2 to -3 C readings during summer. Temperatures that are 15 to 23 C above average (27 to 40 F) now range all over the Antarctic Peninsula and nearby areas of West Antarctica. Perhaps most dramatic are the 1.5 C readings coming from sections of the C region of the Larsen Ice Shelf bordering the Weddell Sea. There, downslope hurricane-force winds howling over the shelf are helping to spike local temperatures even as sea ice in the Weddell is splintered and shoved away from the Larsen C edge.

West Antarctic Heatwave

(A wave of 20+ C [36+ F] above-average temperatures blankets the vulnerable glaciers of West Antarctica on Friday, September 2nd. This pulse of tropical warmth is enough to drive readings over Antarctica to summertime or warmer ranges during winter, with some regions that typically experience below-freezing temperatures year-round nearing or exceeding the thawing point. Image source: Climate Reanalyzer.)

Larsen C is of particular interest due to a large crack spreading through its main body, threatening to break off a Connecticut-sized chunk of ice and disrupt the stability of the larger ice shelf. The most northerly of the remaining large Antarctic Peninsula ice shelves, this towering mass of frozen water serves to buttress a number of large Antarctic glaciers. Its loss or destabilization would allow these glaciers to increase their speed of ocean discharge and in turn, speed the rate of global sea-level rise. Needless to say, this combination of above-freezing temperatures during winter and hurricane-force winds won’t help to stabilize this now more than 120-kilometer long and hundreds-of-feet-deep crack.

Antarctic_surface_temperature

(Differences between average summer and winter temperatures over Antarctica. For sections of West Antarctica near the Antarctic Peninsula, Friday through Sunday will see temperatures more typical to Antarctic summer — during late winter. Image source: European Center for Medium-Range Weather Forecasts.)

A Winter of West Antarctic Heat — Larger South Pole Warm-up on the Way?

More broadly, warming this region to above freezing for extended periods is a concern among glaciologists. In the past (during the Pliocene and Miocene), when atmospheric CO2 levels have hit a range of 390-405 parts per million or above, West Antarctica (and ultimately East Antarctica) experienced warmth which resulted in seas that were many feet and meters higher than today. With atmospheric CO2 readings likely to average near 405 ppm during 2016 (or total greenhouse gas levels in the range of 490 ppm CO2e), it appears that frequent periods of summer-like temperatures and related increasing melt pressure are now possible during polar winter.

Over recent months, this section of Antarctica has been clobbered repeatedly by such spates of above-normal temperatures. Back in June, an odd Jet Stream excursion (gravity wave) pulled a big pulse of Equatorial heat over West Antarctica. Today’s event is just one of a number of recent big warm air invasions into this highly vulnerable zone.

CFSv2 Hot South Pole Summer

(More severe melt stress for Antarctic glaciers? NOAA’s CFSv2 model shows a ridiculously hot South Pole summer may be on the way. Side note — over the past year or so this forecast model has run somewhat cooler than actual temperatures for the Arctic region. Image source: NOAA.)

Taking this most recent warming event into context and looking forward into late 2016 and early 2017, at least one global forecast model is predicting a period of severe Antarctic warming during this time. NOAA’s CFSv2 model, for example, finds a very extreme Antarctic temperature spike emerging over pretty much all of Antarctica during the late Southern Hemisphere summer and early fall months of 2017.

Links:

Earth Nullschool

Climate Reanalyzer

European Center for Medium-Range Weather Forecasts

Another Blow to Glacial Stability

NOAA

Weather data provided by the Global Forecast System Model

Another Blow to Antarctic Glacial Stability as Larsen C Ice Shelf Cracks Up

Larsen C rift

(Northern edge of Larsen C Ice Shelf is at significant risk of breaking off as a massive rift continues to open within it. The above image shows the rate of rift propagation since November of 2010. Image source: Cryosphere Discussions.)

There’s a 30 kilometer long and hundreds foot deep crack running through West Antarctica’s massive Larsen C ice shelf.

It’s a rift that now stretches from the Weddell Sea — where winds and currents have driven human-warmed ocean waters to up-well along the ocean-contacting faces of the great Antarctic ice sheets — and deep into the interior of this 49,000 square kilometer and 600 to 700 foot tall block of ancient, floating ice.

Over the past few years this rift has been rapidly advancing at a rate of about 2.5 kilometers each year.  Given that the rift has already traversed more than half of the Larsen C ice shelf calving face, a very large break-up could now occur at almost any time.

Larsen C Destabilizing

This evolving situation now threatens to destabilize the entire Larsen C ice shelf — resulting in major losses to a very large block of ice that has been a permanent feature of the Antarctic coastline since at least the last interglacial period 150,000 years ago. Such rapidly evolving risk was the subject of a February 5 communication by a group of glaciologists warning that “significant threats” to “Larsen C ice sheet stability” now existed.

The report notes:

In a change from the usual pattern, a northwards-propagating rift from Gipps Ice Rise has recently penetrated through the suture zone and is now more than halfway towards calving off a large section of the ice shelf (Figs. 1 and 2). The rate of propagation of this rift accelerated during 2014. When the next major calving event occurs, the Larsen C Ice Shelf is likely to lose around 10 % of its area to reach a new minimum both in terms of direct observations, and possibly since the last interglacial period (Hodgson et al.2006)

Connecticut-Sized Break-up Possible

Large ice shelf break-ups have been occurring along the Antarctic Peninsula since the 1970s. As human warming advanced and the heat sink of the southern Ocean increased bottom water temperatures along the Antarctic perimeter, many of the far northern ice shelves and an increasing number of ice bodies closer to the Antarctic interior have lost significant portions of their mass.

Now, Larsen C is at risk of an even worse break-up. For the predicted 10% loss to Larsen C would equate to about 5,000 square kilometers — or an area roughly the size of Connecticut — floating off into the Southern Ocean:

Section of Larsen C vulnerable to break-up

(Larsen C Ice Shelf map with the new rift indicated in red and the potential calving face outlined in blue. Note the previous calving fronts in 1975 and 1988. Image source: Cryosphere Discussions)

It would be yet one more major ice loss for the region, and perhaps a new record loss for an area that has frequently seen Rhode Island sized chunks of ice (around 1,000 square kilometers) break off into the warming world’s seas.

The report goes into further detail about the importance and vulnerability of Larsen C, stating:

The Larsen C Ice Shelf is the most northerly of the remaining major Antarctic Peninsula ice shelves and is vulnerable to changes both to ocean and atmospheric forcing (Holland et al., 2015). It is the largest ice shelf in the region and its loss would lead to a significant drawdown of ice from the Antarctic Peninsula Ice Sheet (APIS). There have been observations of widespread thinning (Shepherd et al., 2003; Pritchard et al., 2012; Holland et al., 2015), melt ponding in the northern inlets (Holland et al., 2011; Luckman et al., 2014), and a speed-up in ice flow (Khazendar et al., 2011), all processes which have been linked to former ice shelf collapses (e.g. van den Broeke, 2005).(Emphasis Added).

Conditions in Context

As mentioned above, during recent years we have seen numerous ice shelves and ice sheets begin to destabilize. In addition, two ice shelves — Larsen A and Larsen B have already completely disintegrated due to human-caused warming.

Larsen C may be most immediately at risk, but the leading edges of the Ronne-Filchner Ice Shelf, The Pine Island Glacier, The Ross Ice Shelf, and the Amery glacier have all shown rapid seaward acceleration. Further, various studies of these increasingly vulnerable ice shelves have shown substantial basal melt coincident with a floating of the ice sheets off grounding lines, leading to a retreat of the anchor points landward.

Major Antarctic Ice Shelves

(Antarctica’s major ice shelves. Image source: Commons.)

Sea-facing ice sheets and ice shelves serve to anchor the great interior glaciers of Antarctica. Loss or destabilization of these anchors would result in more and more rapid flow of land ice into the Southern Ocean. It is for this reason that the destabilization and shattering of ice shelves like Larsen C can have serious implications for the rate of sea level rise over the coming decades.

Overall, nearly 200 feet worth of sea level rise is locked in Antarctica’s glaciers and we are, through a heating of the world’s oceans, ice, and atmosphere, pushing these glaciers to melt and move in an ever-more dramatic and world-altering fashion.

Links:

Newly Developing Rift in Larsen C Ice Shelf Presents Significant Risk to Stability

Shrinking Ice Shelves and The Pine Island Glacier

Commons: The Larsen C Ice Shelf

Hat-tip to Colorado Bob

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