Collapsing Greenland Zachariae Isstrom glacier could raise sea levels by half a metre, say scientists

Huge Zachariae Isstrom glacier has begun to break up, starting a rapid retreat that could continue to raise sea levels for decades to come



A major glacier in Greenland that holds enough water to raise global sea levels by half a metre has begun to crumble into the North Atlantic Ocean, scientists say.

by Ian Sample, science editor, The Guardian, November 12, 2015

The huge Zachariae Isstrom glacier in northeast Greenland started to melt rapidly in 2012 and is now breaking up into large icebergs where the glacier meets the sea, monitoring has revealed.

The calving of the glacier into chunks of floating ice will set in train a rise in sea levels that will continue for decades to come, the US team warns.

“Even if we have some really cool years ahead, we think the glacier is now unstable,” said Jeremie Mouginot at the University of California, Irvine. “Now this has started, it will continue until it retreats to a ridge about 30km back which could stabilise it and perhaps slow that retreat down.”

Mouginot and his colleagues drew on 40 years of satellite data and aerial surveys to show that the enormous Zachariae Isstrom glacier began to recede three times faster from 2012, with its retreat speeding up by 125 metres per year every year until the most recent measurements in 2015.

The same records revealed that from 2002 to 2014 the area of the glacier’s floating shelf shrank by a massive 95%, according to a report in the journal Science. The glacier has now become detached from a stabilising sill and is losing ice at a rate of 4.5 billion tons a year.

Eric Rignot, professor of Earth system science at the University of California, Irvine, said that the glacier was “being hit from above and below,” with rising air temperatures driving melting at the top of the glacier, and its underside being eroded away by ocean currents that are warmer now than in the past.

“The glacier is now breaking into bits and pieces and retreating into deeper ground,” he said. The rapid retreat is expected to continue for 20 to 30 more years, until the glacier reaches another natural ledge that slows it down.

The scientists recreated the history of the glacier from aerial radar, gravitational measurements and laser profiles, and from radar and optical images taken from space. The combined data reveal the changing shape, size and position of Greenland glaciers over the past four decades.

To the north of Zachariae Isstrom, the scientists studied a second large glacier called Nioghalvfjerdsfjorden. Together, the two glaciers drain a region of nearly 200,000 sq km, amounting to 12% of the Greenland ice sheet. Were both to melt, they would contribute a full metre to global sea levels.

The monitoring showed that Nioghalvfjerdsfjorden glacier was also melting rapidly, but retreating more slowly than Zachariae Isstrom along uphill terrain. If the thinning continues at today’s pace, the scientists believe the ice shelf will become vulnerable to break up in the near future.

The bleak assessment of the glaciers’ retreat comes only months after NASA launched an urgent 6-year project called "Oceans Melting Greenland" (aptly contracted to OMG), to understand the processes that drive the loss of Greenland ice.

https://www.theguardian.com/environment/2015/nov/12/collapsing-greenland-glacier-could-raise-sea-levels-by-half-a-metre-say-scientists

James Hansen: ‘Emergency Cooperation Among Nations’ Is Needed to Prevent Catastrophic Sea Level Rise

“Roughly 10 feet of sea level rise—well beyond previous estimates—would render coastal cities such as New York, London, and Shanghai uninhabitable.” Photo credit: Woodbine

by Jon Queally, Common Dreams, July 21, 2015

If a new scientific paper is proven accurate, the international target of limiting global temperatures to a 2 °C rise this century will not be nearly enough to prevent catastrophic melting of ice sheets that would raise sea levels much higher and much faster than previously thought possible.

According to the new study—which has not yet been peer-reviewed, but was written by former NASA scientist James Hansen and 16 other prominent climate researchers—current predictions about the catastrophic impacts of global warming, the melting of vast ice sheets and sea level rise do not take into account the feedback loop implications of what will occur if large sections of Greenland and the Antarctic are consumed by the world’s oceans.

A summarized draft of the full report was released to journalists on Monday, with the shocking warning that such glacial melting will “likely” occur this century and could cause as much as a 10 foot sea-level rise in as little as 50 years. Such a prediction is much more severe than current estimates contained in reports issued by the Intergovernmental Panel on Climate Change (IPCC) — the UN-sponsored body that represents the official global consensus of the scientific community.

“If the ocean continues to accumulate heat and increase melting of marine-terminating ice shelves of Antarctica and Greenland, a point will be reached at which it is impossible to avoid large scale ice sheet disintegration with sea level rise of at least several meters,” the paper states.

Separately, the researchers conclude that “continued high emissions will make multi-meter sea level rise practically unavoidable and likely to occur this century. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.”

The Daily Beast‘s Mark Hertsgaard, who attended a press call with Dr. Hansen on Monday, reports that the work presented by the researchers is

"...warning that humanity could confront “sea level rise of several meters” before the end of the century unless greenhouse gas emissions are slashed much faster than currently contemplated.

This roughly 10 feet of sea level rise—well beyond previous estimates—would render coastal cities such as New York, London, and Shanghai uninhabitable. “Parts of [our coastal cities] would still be sticking above the water,” Hansen said, “but you couldn’t live there.”

This apocalyptic scenario illustrates why the goal of limiting temperature rise to 2 degrees Celsius is not the safe “guardrail” most politicians and media coverage imply it is, argue Hansen and 16 colleagues in a blockbuster study they are publishing this week in the peer-reviewed journal Atmospheric Physics and Chemistry. On the contrary, a 2C future would be “highly dangerous.”

If Hansen is right—and he has been right, sooner, about the big issues in climate science longer than anyone—the implications are vast and profound.

In the call with reporters, Hansen explained that time is of the essence, given the upcoming climate talks in Paris this year and the grave consequences the world faces if bold, collective action is not taken immediately. “We have a global crisis that calls for international cooperation to reduce emissions as rapidly as practical,” the paper states.

Hansen said he has long believed that many of the existing models were under-estimating the potential impacts of ice sheet melting, and told the Daily Beast: “Now we have evidence to make that statement based on much more than suspicion.”

Though he acknowledged the publication of the paper was unorthodox, Hansen told reporters that the research itself is “substantially more persuasive than anything previously published.”

For his part, Eric Holthaus, a meteorologist who writes about weather and climate for Slate, said the “bombshell” findings are both credible and terrifying. Holthaus writes:

To come to their findings, the authors used a mixture of paleoclimate records, computer models, and observations of current rates of sea level rise, but “the real world is moving somewhat faster than the model,” Hansen says.

[…] The implications are mindboggling: In the study’s likely scenario, New York City—and every other coastal city on the planet—may only have a few more decades of habitability left. That dire prediction, in Hansen’s view, requires “emergency cooperation among nations.”

In response to the paper, climate scientist Michael Oppenheimer of Princeton University affirmed: “If we cook the planet long enough at about two degrees warming, there is likely to be a staggering amount of sea level rise. Key questions are when would greenhouse-gas emissions lock in this sea level rise and how fast would it happen? The latter point is critical to understanding whether and how we would be able to deal with such a threat.”

The new research, Oppenheimer added, “takes a stab at answering the ‘how soon?’ question but we remain largely in the dark. Giving the state of uncertainty and the high risk, humanity better get its collective foot off the accelerator.”

And as the Daily Beast‘s Hertsgaard notes, Hansen’s track record on making climate predictions should command respect from people around the world. The larger question, however, is whether humanity has the capacity to act.

“The climate challenge has long amounted to a race between the imperatives of science and the contingencies of politics,” Hertsgaard concludes. “With Hansen’s paper, the science has gotten harsher, even as the Nature Climate Change study affirms that humanity can still choose life, if it will. The question now is how the politics will respond—now, at Paris in December, and beyond.”

http://ecowatch.com/2015/07/21/james-hansen-climate-report/

WaPo: The melting of Antarctica was already really bad. It just got worse

by Chris Mooney, The Washington Post, March 16, 2015

A satellite view of Antarctica is seen in this undated NASA handout photo obtained by Reuters on February 6, 2012. (NASA handout via Reuters)

This story has been updated.

A hundred years from now, humans may remember 2014 as the year that we first learned that we may have irreversibly destabilized the great ice sheet of West Antarctica, and thus set in motion more than 10 feet of sea level rise.

Meanwhile, 2015 could be the year of the double whammy — when we learned the same about one gigantic glacier of East Antarctica, which could set in motion roughly the same amount all over again. Northern Hemisphere residents and Americans in particular should take note — when the bottom of the world loses vast amounts of ice, those of us living closer to its top get more sea level rise than the rest of the planet, thanks to the law of gravity.

The findings about East Antarctica emerge from a new paper just out in Nature Geoscience by an international team of scientists representing the United States, Britain, France and Australia. They flew a number of research flights over the Totten Glacier of East Antarctica — the fastest-thinning sector of the world’s largest ice sheet — and took a variety of measurements to try to figure out the reasons behind its retreat. And the news wasn’t good: It appears that Totten, too, is losing ice because warm ocean water is getting underneath it.

“The idea of warm ocean water eroding the ice in West Antarctica, what we’re finding is that may well be applicable in East Antarctica as well,” says Martin Siegert, a co-author of the study and who is based at the Grantham Institute at Imperial College London.

[Research casts alarming light on the decline of West Antarctic glaciers]

The floating ice shelf of the Totten Glacier covers an area of 90 miles by 22 miles. It it is losing an amount of ice “equivalent to 100 times the volume of Sydney Harbour every year,” notes the Australian Antarctic Division.

That’s alarming, because the glacier holds back a much more vast catchment of ice that, were its vulnerable parts to flow into the ocean, could produce a sea level rise of more than 11 feet — which is comparable to the impact from a loss of the West Antarctica ice sheet. And that’s “a conservative lower limit,” says lead study author Jamin Greenbaum, a PhD candidate at the University of Texas at Austin.

In its alignment with the land and the sea, the Totten Glacier is similar to the West Antarctic glaciers, which also feature ice shelves that slope out from the vast sheet of ice on land and extend into the water. These ice shelves are a key source of instability, because if ocean waters beneath them warm, they can lose ice rapidly, allowing the ice sheet behind them to flow more quickly into the sea.

The researchers used three separate types of measurements taken during their flights — gravitational measurements, radar and laser altimetry — to get a glimpse of what might be happening beneath the massive glacier, whose ice shelves are more than 1,600 feet thick in places. Using radar, they could measure the ice’s thickness. Meanwhile, by measuring the pull of the Earth’s gravity on the airplane in different places, the scientists were able to determine just how far below that ice the seafloor was.

The result was the discovery of two undersea troughs or valleys beneath the ice shelf — regions where the seafloor slopes downward, allowing a greater depth of water beneath the floating ice. These cavities or subsea valleys, the researchers suggest, may explain the glacier’s retreat — they could allow warmer deep waters to get underneath the ice shelf, accelerating its melting.

Aerial photo of Totten Glacier’s ice shelf edge taken during one of the team’s geophysical survey flights. (Jamin Greenbaum)

In this particular area of Antarctica, Greenbaum says, a warmer layer of ocean water offshore is actually deeper than the colder layers above it, because of the saltwater content of the warm water (which increases its density). And the canyons may allow that warm water access to the glacier base. “What we found here is that there are seafloor valleys deeper than the depth of the maximum temperature measured near the glacier,” Greenbaum says.

One of these canyons is three miles wide, in a region that was previously believed to simply hold ice lying atop solid earth. On the contrary, the new study suggests the ice is instead afloat.

The availability of warm water, and the observed melting, notes the study, “support the idea that the behaviour of Totten Glacier is an East Antarctic analogue to ocean-driven retreat underway in the West Antarctic Ice Sheet (WAIS). The global sea level potential of 3.5 m flowing through Totten Glacier alone is of similar magnitude to the entire probable contribution of the WAIS.”

For Richard Alley, a glaciologist at Penn State University, the new research hints at a possible solution to a question that scientists have long had about the planet’s past — and in particular the Pliocene epoch, beginning 5.3 million years ago, when sea levels were dramatically higher, by as much as 40 meters.

“The sea-level indicators from the Pliocene have suggested that an important amount of ice came out of East Antarctica into the ocean,” says Alley. “Sedimentary records offshore pointed in the same way, and recent modeling…shows the strong potential for this to have happened.  This new paper adds to the evidence — the pieces are fitting together.”

One limitation of the study is that the scientists were not able to directly measure the temperature of ocean water that is reaching the glacier itself. While this could be done with robotic underwater vehicles or other methods, that wasn’t part of the study at this time. Thus, the conclusions are more focused on inferring the vulnerability of the glacier based on a number of different pieces of evidence — topped off by the fact that the glacier is, indeed, retreating.

“What we need now is a confirmation of the findings of the paper from oceanographic data, because it  is one thing to find potential pathways for warm water to intrude the cavity, it is another to show that this is actually happening,” observes Eric Rignot, an Antarctica expert at the University of California, Irvine. “This paper comes short of the latter, but other research efforts are underway to get critical oceanographic information near Totten.”

[These subsea drones are figuring out just how badly we are messing up the planet]

Maximum Antarctic sea ice 2014(0:42)

An animation of the Antarctic sea ice between March 21 and September 19, 2014, when the sea ice reached its maximum extent. The red extent line shows the average of the annual maximum extents from 1979 through 2014. (NASA)

For residents of the United States — and indeed, the entire Northern Hemisphere — the impact of major ice loss from Antarctica could be dire. If Antarctica loses volumes of ice that would translate into major contributions to sea level rise, that rise would not be distributed evenly around the globe. The reason is the force of gravity. Antarctica is so massive that it pulls the ocean toward it, but if it loses ice, that gravitational pull will relax, and the ocean will slosh back toward the Northern Hemisphere — which will experience additional sea level rise.

For the United States, the amount of sea level rise could be 25 percent or more than the global average.

[The U.S. has caused more global warming than any other country. Here's how the Earth will get its revenge.]

Much as with the ocean-abutting glaciers of West Antarctica, just because a retreat has been observed — and because the entirety of the region implies a sea level rise of 11 or more feet were all ice to end up in the ocean — does not mean that we’ll see anything near that much sea level rise in our lifetimes. These processes generally are expected to play out over hundreds of years or more. They would reshape the face of the Earth – but we may never see it.

The problem, then, is more the world we’re leaving to our children and grandchildren — because once such a gigantic geophysical process begins, it’s hard to see how it comes to a halt. “With warming oceans, it’s difficult to see how a process that starts now would be reversed, or reversible, in a warming world,” Siegert says.

Update: This article was updated to correct the size of the Totten Glacier. According to Greenbaum (but contrary to this press release), its floating portion (or ice shelf) is 90 miles by 22 miles in size. 

http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/

Robert Schribbler: Warm Water Rising From the Depths: Much of Antarctica Now Under Threat of Melt

by Robert Schribbler, Robert Schribbler's blog, December 5, 2014

Antarctica. A seemingly impregnable fortress of cold. Ice mountains rising 2,100 meters high. Circumpolar winds raging out from this mass of chill frost walling the warm air out. And a curtain of sea ice insulating the surface air and mainland ice sheets from an increasingly warm world. A world that is now on track to experience one of its hottest years on record.

Antarctica, the coldest place on Earth, may well seem impregnable to this warming. But like any other fortress, it has its vulnerable spots. In this case, a weak underbelly. For in study after study, we keep finding evidence that warm waters are rising up from the abyss surrounding the chill and frozen continent. And the impact and risk to Antarctica’s glacial ice mountains is significant and growing.

(Collapse of ice structure at the leading edge of the Filchner-Ronne Ice Shelf adjacent to a rapidly warming Weddell Sea during January of 2010. A new study has found warm water upwelling from the Circumpolar Deep Water is rapidly approaching this massive ice shelf. Loss of Filchner-Ronne and its inland buttressed glaciers would result in 10 feet of sea level rise. Image source: Commons.)

For a study this week confirmed that Antarctica is now seeing a yearly loss of ice equal to one half the volume of Mt Everest every single year. A rate of loss triple that seen just ten years ago. An acceleration that, should it continue, means a much more immediate threat to coastal regions from sea level rise than current IPCC projections now estimate.

Shoaling of the Circumpolar Deep Water

The source of this warm water comes from a deep-running current that encircles all of Antarctica. Called the Circumpolar Deep Water, this current runs along the outside margin of the continental shelf. Lately, the current has been both warming and rising up the boundaries of the continental zone. And this combined action is rapidly bringing Antarctica’s great ice sheets under increasing threat of more rapid melt.

According to a new study led by Sunke Schmidtko, this deep water current has been warming at a rate of 0.1 degrees Celsius per decade since 1975. Even before this period of more rapid deep water warming, the current was already warmer than the continental shelf waters near Antarctica’s great glaciers. With the added warming, the Circumpolar Deep Water boasts temperatures in the range of 33 to 35 degrees Fahrenheit — enough heat to melt any glacier it contacts quite rapidly.

Out in the deep ocean waters beyond the continental shelf zone surrounding Antarctica, the now warmer waters of this current can do little to effect the great ice sheets. Here Sunke’s study identifies the crux of the problem — the waters of the Circumpolar Deep Water are surging up over the continental shelf margins to contact Antarctica’s sea fronting glaciers and ice shelves with increasing frequency.

In some cases, these warm waters have risen by more than 300 feet up the continental shelf margins and come into direct contact with Antarctic ice — causing it to rapidly melt. This process is most visible in the Amundsen Sea where an entire flank of West Antarctica is now found to be undergoing irreversible collapse. The great Pine Island Glacier, the Thwaites Glacier and many of its tributaries altogether composing enough ice to raise sea levels by 4 feet are now at the start of their last days. All due to an encroachment of warm water rising up from the abyss.

(Antarctic rivers of ice. Rising and warming waters from the Circumpolar Deep Water along continental margins have been increasingly coming into contact with ice shelf and glacier fronts that float upon or face the surrounding seas. The result has been much higher volumes of melt water contributions than expected from Antarctica. Image source: University of California.)

But the warm water rise is not just isolated to the Amundsen Sea. For Sunke also found that the warm water margin in the Weddell Sea on the opposite flank of West Antarctica was also rapidly on the rise. From 1980 to 2010, this warm water zone had risen from a depth of about 2100 feet to less than 1100 feet. A rapid advance toward another massive concentration of West Antarctic ice.

The impacts of a continued rise of this kind can best be described as chilling.

Sunke notes in an interview with National Geographic:

If this shoaling rate continues, there is a very high likelihood that the warm water will reach the Filchner Ronne Ice Shelf, with consequences which are huge.

Filchner Ronne, like the great Pine Island Glacier, has been calving larger and larger ice bergs during recent years. Should warm waters also destabilize this vast ice shelf another 1.5 feet of sea level rise would be locked in due to its direct loss. Including the massive inland glaciers that Filchner Ronne buttresses against a seaward surge, much larger than the ones near the Amundsen sea, would add a total of 10 feet worth of additional sea level rise.

Together, these destabilized zones would unleash much of West Antartica and some of Central Antartica, resulting in as much as 14 feet of sea level rise over a 100 to 200 year timeframe. This does not include Greenland, which is also undergoing rapid destabilization, nor does it include East Antarctica — which may also soon come under threat due to the encroachment of warm waters rising from the depths.

Are IPCC Projected Rates of Sea Level Rise Too Conservative?

The destabilization of glaciers along the Amundsen sea, the imminent threat to the Filchner Ronne Ice Shelf, and the less immediate but still troubling threat to East Antarctica’s glaciers, together with a rapidly destabilizing Greenland Ice Sheet, calls into question whether current IPCC predictions for sea level rise before 2100 are still valid.

IPCC projects a rise in seas of 1-3 feet by the end of this Century. But much of that rise is projected to come from thermal expansion of the world’s oceans — not from ice sheet melt in Antarctica and Greenland. Current rates of sea level rise of 3.3 milimeters each year would be enough to hit 1 foot of sea level rise by the end of this Century. However, just adding in the melting of the Filchner Ronne — a single large ice shelf — over the same period would add 4.4 milimeters a year. Add in a two century loss of the Amundsen glaciers — Pine Island and Thwaites — and we easily exceed the three foot mark by 2100.

Notably, this does not include the also increasingly rapid loss of ice coming from Greenland, the potential for mid century additions from East Antarctica, or lesser but still important additions from the world’s other melting glaciers.

Such more rapid losses to ice sheets may well reflect the realities of previous climates. At current CO2e levels of 481 ppm (400 ppm CO2 + methane and other human greenhouse gas additions) global sea levels were as much as 75-120 feet higher than they are today. Predicted greenhouse gas levels of 550 to 600 ppm CO2e by the middle of this century (Breaking 550 ppm CO2 alone by 2050 to 2060) are enough to set in place conditions that would eventually melt all the ice on Earth and raise sea levels by more than 200 feet. For there was no time in the past 55 million years when large ice sheets existed under atmospheric CO2 concentrations exceeding 550 parts per million.

Glaciologist Eric Rignot has been warning for years that the IPCC sea level rise estimates may well be too conservative. And it seems that recent trends may well bear his warnings out. If so, the consequences to millions of people living along the world’s coastlines are stark and significant. For the world, it appears we face the increasing likelihood of a near-term inland mass-migration of people and property. A stunning set of losses and tragedy starting now and ongoing through many decades and centuries to come.

Links:

Warming Seas Drive Rapid Acceleration of Melting Antarctic Ice

Mass Loss of the Amundsen Sea Embayment of West Antarctica

Multidecadal Warming of Antarctic Waters

Research Casts Alarming Light on Decline of West Antarctic Glaciers

Antarctic Ice Shelf Being Eaten Away by Sea

http://robertscribbler.wordpress.com/2014/12/05/warm-water-rising-from-the-depths-much-of-antarctica-now-under-threat-of-melt/

NASA: Antarctic Melt Loss Triples in a Decade

by Peter Sinclair, Climate Crocks, December 3, 2014

Evidence is piling up indicating the planet will be extremely fortunate to stay on the lower end of sea level rise estimates.

And remember, this study covers just one area of Antarctica, where we have good instrument coverage.

NASA:

A comprehensive, 21-year analysis of the fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade. 

The glaciers in the Amundsen Sea Embayment in West Antarctica are hemorrhaging ice faster than any other part of Antarctica and are the most significant Antarctic contributors to sea level rise. This study by scientists at the University of California, Irvine (UCI), and NASA is the first to evaluate and reconcile observations from four different measurement techniques to produce an authoritative estimate of the amount and the rate of loss over the last two decades.

This work extends the work of Eric Rignot, who stunned the ice sheet community last spring with his “holy shit moment” paper on unstoppable Antarctic melting – discussed here in a very important video, if you have not seen it.

NASA again:

“The mass loss of these glaciers is increasing at an amazing rate,” said scientist Isabella Velicogna, jointly of UCI and NASA’s Jet Propulsion Laboratory, Pasadena, California. Velicogna is a coauthor of a paper on the results, which has been accepted for publication in the journal Geophysical Research Letters. 

Lead author Tyler Sutterley, a doctoral candidate at UCI, and his team did the analysis to verify that the melting in this part of Antarctica is shifting into high gear. “Previous studies had suggested that this region is starting to change very dramatically since the 1990s, and we wanted to see how all the different techniques compared,” Sutterley said. “The remarkable agreement among the techniques gave us confidence that we are getting this right.” 

The researchers reconciled measurements of the mass balance of glaciers flowing into the Amundsen Sea Embayment. Mass balance is a measure of how much ice the glaciers gain and lose over time from accumulating or melting snow, discharges of ice as icebergs, and other causes. Measurements from all four techniques were available from 2003 to 2009. Combined, the four data sets span the years 1992 to 2013.

Worth watching this video from a year ago if you have not yet, backgrounder on the movement of large ice sheets.

The glaciers in the embayment lost mass throughout the entire period. The researchers calculated two separate quantities: the total amount of loss, and the changes in the rate of loss. 

The total amount of loss averaged 83 gigatons per year (91.5 billion U.S. tons). By comparison, Mt. Everest weighs about 161 gigatons, meaning the Antarctic glaciers lost an amount of water weight equivalent to Mt. Everest every two years over the last 21 years. 

The rate of loss accelerated an average of 6.1 gigatons (6.7 billion U.S. tons) per year since 1992.

During the period when the four observational techniques overlapped, the melt rate increased an average of 16.3 gigatons per year — almost three times the rate of increase for the full 21-year period. The total amount of loss was close to the average at 84 gigatons. 

The four sets of observations include NASA’s Gravity Recovery and Climate Experiment satellites, laser altimetry from NASA’s Operation IceBridge airborne campaign and the earlier ICESat satellite, radar altimetry from the European Space Agency’s Envisat satellite, and mass budget analyses using radars and the University of Utrecht’s Regional Atmospheric Climate Model. 

The scientists noted that glacier and ice sheet behavior worldwide is by far the greatest uncertainty in predicting future sea level. “We have an excellent observing network now. It’s critical that we maintain this network to continue monitoring the changes,” Velicogna said, “because the changes are proceeding very fast.”

This is just Antarctica. At the other pole, Greenland is also vulnerable, and estimates of how fast it can shed mass keep increasing. Below, see Dr. Jeff Masters' analysis of that loss, and Dr. James Hansen’s take on what an accelerating Greenland loss might mean to the world.

Dr. Jeff Masters at Weather Underground:

Human-caused global warming has set in motion an unstoppable slow-motion collapse of the glaciers in West Antarctica capable of raising global sea level by 4 feet (1.2 meters) in a few hundred years, said NASA in a May 2014 press release. What’s more, one of the glaciers involved, the Thwaites Glacier, acts as a linchpin on the rest of the ice sheet, which contains enough ice to cause a total of 10 to 13 feet (3 to 4 meters) of global sea level rise over a period of centuries. This unstoppable collapse makes saving Greenland “absolutely essential,” said glaciologist Richard Alley in a May 2014 interview in Mother Jones. 

Greenland’s ice sheet holds enough water to raise global sea levels by 7.36 meters (24.15 feet) were it all to melt, and civilization would be hard-pressed to deal with 10–13 feet of sea level rise from West Antarctica, let alone another 20+ feet from Greenland. “If we’ve committed to 3.3 meters (10.8') from West Antarctica, we haven’t committed to losing Greenland, we haven’t committed to losing most of East Antarctica,” said Alley. “Those are still out there for us. And if anything, this new news just makes our decisions more important, and more powerful.” 

Unfortunately, the Greenland Ice Sheet is much more vulnerable to melting than previously thought, found a May 2014 study by Morlighem et al., "Deeply incised submarine glacial valleys beneath the Greenland ice sheet." The researchers found that widespread ice-covered valleys extend much deeper below sea level and farther inland than previously thought, and would likely melt significantly from steadily warming waters lapping at Greenland’s shores.

Figure 2. Monthly changes in the total mass (in gigatons) of the Greenland ice sheet estimated from GRACE satellite measurements between March 2002–July 2013. The blue and orange asterisks denote April and July values, respectively. Note that the decline in ice mass lost from Greenland is not a straight line – it is exponential, meaning that, in general, more ice loss is lost each year than in the previous year. However, the mass loss during the 2013 summer melt season was probably smaller than during 2012, said the 2013 Arctic Report Card.

Dr. James Hansen:

Fig. 1 shows that Greenland has been losing mass at a faster and faster rate over the past decade, with the recent rate corresponding to ~1 mm sea level per year (1 mm sea level = 360 Gt ice). The linear fit to the Shepherd et al. data in Fig. 1 yields a Greenland contribution to global sea level of about 30 cm by 2100.

Fig. 1. Annual mass change of Greenland ice sheet based on the input–output method, an analysis of gravity measurements, and a best-estimate composite (Shepherd et al., 2012).

The increasing Greenland mass loss in Fig. 1 can be fit just as well by exponentially increasing annual mass loss, a behavior that Hansen (2005, 2007) argues could occur because of multiple amplifying feedbacks as an ice sheet begins to disintegrate. A 10-year doubling time would lead to 1 meter sea level rise by 2067 and 5 meters by 2090. The dates are 2045 and 2057 for 5-year doubling time and 2055 and 2071 for a 7-year doubling time.

http://climatecrocks.com/2014/12/03/nasa-antarctic-melting-triples/ 

Peter Sinclair: Point of No Return, Deglaciation of West Antarctica, Meltwater Pulse 2B

by Peter Sinclair, This Is Not Cool, June 2, 2014

Today’s news will be dominated by discussion of new carbon regulations proposed by the Obama administration.  My contribution is to summarize the most recent evidence for why those regs are needed today, if not 25 years ago.

Bud Ward at Yale Climate Connections:

It’s not often that a scientific research paper generates the kind of media attention and scientific community buzz that resulted from a recent study on the apparent inevitability of substantial Antarctic glacial melting.

The early May research headed by lead author Eric Rignot of NASA called attention to melting now under way in Antarctica that CBS News anchor Scott Pelley reported “cannot be stopped.”

“Scientists say the situation is almost certainly unstoppable,” NBC News Anchor Brian Mitchell reported.

Rignot cautioned that the research indicates “we’ve passed the point of no return … It’s just a matter of time before these glaciers disappear to the sea.” While he indicated that the full melt, at the current pace, might not occur for two centuries, he pointed too to evidence suggesting the likelihood of an accelerating pace.

“There’s probably nothing that can be done to stop this,” Rignot said.

“This is really happening,” lead NASA lead polar ice researcher Tom Wagner said. “This weak underbelly of Antarctica is in fact starting to float out into the sea, and there’s not a lot to hold it back.”

A “This is Not Cool” video on the report by independent videographer Peter Sinclair is the first to be posted under the new Yale Climate Connections name, formerly The Yale Forum on Climate Change & The Media. The official transition to that newly named site is to get underway over the next few weeks, initially with a largely cosmetic rebranding, then to be followed by a substantial overhaul and a more multi-media emphasis aimed at better reaching the general public.

Note: link to the Guardian piece referenced in the video is here. Errata – I neglected to thank the European Space Agency for important video animations. Deepest apologies.

UPDATE: Per Stefan Rahmstorf, newly published study adds complexity.

eScience News:

“Conventional thinking based on past research is that the Antarctic Ice Sheet has been relatively stable since the last ice age, that it began to melt relatively late during the deglaciation process, and that its decline was slow and steady until it reached its present size,” said lead author Michael Weber, a scientist from the University of Cologne in Germany.

“The sediment record suggests a different pattern — one that is more episodic and suggests that parts of the ice sheet repeatedly became unstable during the last deglaciation,” Weber added.

The research also provides the first solid evidence that the Antarctic Ice Sheet contributed to what is known as meltwater pulse 1A, a period of very rapid sea level rise that began some 14,500 years ago, according to Peter Clark, an Oregon State University paleoclimatologist and co-author on the study.

The largest of the 8 episodic pulses outlined in the new Nature study coincides with meltwater pulse 1A.

“During that time, the sea level on a global basis rose about 50 feet in just 350 years — or about 20 times faster than sea level rise over the last century,” noted Clark, a professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences. “We don’t yet know what triggered these eight episodes or pulses, but it appears that once the melting of the ice sheet began it was amplified by physical processes.”

The researchers suspect that a feedback mechanism may have accelerated the melting, possibly by changing ocean circulation that brought warmer water to the Antarctic subsurface, according to co-author Axel Timmermann, a climate researcher at the University of Hawaii at Manoa.

“This positive feedback is a perfect recipe for rapid sea level rise,” Timmermann said.

Some 9,000 years ago, the episodic pulses of melting stopped, the researchers say.

“Just as we are unsure of what triggered these eight pulses,” Clark said, “we don’t know why they stopped. Perhaps the sheet ran out of ice that was vulnerable to the physical changes that were taking place. However, our new results suggest that the Antarctic Ice Sheet is more unstable than previously considered.”

http://climatecrocks.com/2014/06/02/new-video-meltwater-pulse-2b/http://climatecrocks.com/2014/06/02/new-video-meltwater-pulse-2b/