Chris Mooney, WaPo: Earth Is 'Missing' at Least 20 Ft of Sea Level Rise. Antarctica Could Be The Time Bomb

by Chris Mooney, The Washington Post, February 12, 2019

Some 115,000 years ago, Homo sapiens were still living in bands of hunter gatherers, largely confined to Africa. We still shared the globe with the Neanderthals, although it's not clear we had met them yet.

And though these various hominids didn't know it, the Earth was coming to the end of a major warm period. It was one that's quite close to our current climate, but with one major discrepancy - seas at the time were 20 to 30 feet (6 to 9 metres) higher.

During this ancient period, sometimes called the Eemian, the oceans were about as warm as they are today.

And last month, intriguing new research emerged suggesting that Northern Hemisphere glaciers have already retreated just as far as they did in the Eemian, driven by dramatic warming in Arctic regions.

The finding arose when a team of researchers working on Baffin Island, in northeastern Canada, sampled the remains of ancient plants that had emerged from beneath fast-retreating mountain glaciers.

And they found that the plants were very old indeed, and had probably last grown in these spots some 115,000 years ago.

That's the last time the areas were actually not covered by ice, the scientists believe.

"It's very hard to come up with any other explanation, except that at least in that one area where we're working ... the last century is as warm as any century in the last 115,000 years," said Gifford Miller, a geologist at the University of Colorado in Boulder who led the research on Baffin Island.

But if Miller is right, there's a big problem. We have geological records of sea levels from the Eemian. And the oceans, scientists believe, were 20 to 30 feet (6 to 9 metres) higher.

Some extra water likely came from Greenland, whose ice currently contains over 20 feet (6 metres) of potential sea level rise. But it couldn't have been just Greenland, because that entire ice sheet did not melt at the time.

That's why researchers also suspect a collapse of the most vulnerable part of Antarctica, the West Antarctic ice sheet. This region could easily supply another 10 feet (3 metres) of sea level rise, or more.

"There's no way to get tens of meters of sea level rise without getting tens of meters of sea level rise from Antarctica," said Rob DeConto, an Antarctic expert at the University of Massachusetts.

Trying to understand how Antarctica will fall

Scientists are now intensely debating precisely which processes could have played out then — and how soon they'll play out again. After all, West Antarctica has already been shown, once again, to be beginning a retreat.

Some researchers, including DeConto, think they have found a key process - called marine ice cliff collapse - that can release a lot of sea level rise from West Antarctica in a hurry.

But they're being challenged by another group, whose members suspect the changes in the past were slow - and will be again.

To understand the dispute, consider the vulnerable setting of West Antarctica itself.

Essentially, it's an enormous block of ice mostly submerged in very cold water. Its glaciers sit up against the ocean in all directions, and toward the center of the ice sheet, the seafloor slopes rapidly downward, even as the surface of the ice sheet itself grows much thicker, as much as two miles thick in total.

As much as a mile and a half of that ice rests below the sea level, but there is still plenty of ice above it, too.

So if the gateway glaciers start to move backward - particularly a glacier named Thwaites, by far the largest of them - the ocean would quickly have access to much thicker ice.

The idea is that during the Eemian, this whole area was not a block of ice at all, but an unnamed sea. Somehow, the ocean got in, toppling the outer glacial defenses, and gradually setting all of West Antarctica afloat and on course to melting.

DeConto, with his colleague David Pollard, built a model that looked to the Eemian, and another ancient warm period called the Pliocene, to try to understand how this could happen.

In particular, they included two processes that can remove glaciers. One, dubbed 'marine ice sheet instability,' describes a situation in which a partially submerged glacier gets deeper and thicker as you move toward its center.

In this configuration, warm water can cause a glacier to move backward and downhill, exposing ever thicker ice to the ocean - and thicker ice flows outward faster.

So the loss feeds upon itself.

Marine ice sheet instability is probably underway already in West Antarctica, but in the model, it wasn't enough. DeConto and Pollard also added another process that they say is currently playing out in Greenland, at a large glacier called Jakobshavn.

Jakobshavn is moving backward down an undersea hill slope, just in the way that it is feared the much larger Thwaites will drift. But Jakobshavn is also doing something else. It is constantly breaking off thick pieces at its front, almost like a loaf of bread, dropping slice after slice.

That's because Jakobshavn no longer has an ice shelf, a floating extension that used to grow out over the ocean at the front of the glacier and stabilize it. The shelf collapsed as Greenland warmed in the past two decades.

As a result, Jakobshavn now presents a steep vertical front to the sea. Most of the glacier's ice is under the water, but more than 100 meters (330 feet) extend above it - and for DeConto and Pollard, that's the problem. That's too much to be sustained.

Ice is not steel. It breaks. And breaks. And breaks.

This additional process, called 'marine ice cliff collapse,' causes an utter disaster if you apply it to Thwaites. If Thwaites someday loses its own ice shelf and exposes a vertical front to the ocean, you would have ice cliffs hundreds of meters above the surface of the water.

DeConto and Pollard say that such cliffs would continually fall into the sea. And when they added this computation, it not only recreated Eemian sea level rise, it greatly increased their projection of how much ice Antarctica could yield in this century - more than three feet.

Since there are other drivers of sea level rise, like Greenland, this meant that we could see as much as six feet in total in this century, roughly double prior projections. And in the next century, the ice loss would get even worse.

"What we pointed out was, if the kind of calving that we see in Greenland today were to start turning on in analogous settings in Antarctica, then Antarctica has way thicker ice, it's a way bigger ice sheet, the consequences would be potentially really monumental for sea level rise," DeConto said.

Moreover, the process, he argues, is essential to understanding the past - and thus how we could replicate it.

"We cannot recreate six meters of sea level rise early in the Eemian without accounting for some brittle fracture in the ice sheet model," said DeConto.

A massive debate over marine ice cliffs

Tamsin Edwards is not convinced. A glaciologist at Kings College London, she is lead author - with a number of other Antarctic experts - of a study published Wednesday in Nature (the same journal that published DeConto and Pollard in 2016) that disputes their model, in great detail.

Using a statistical technique to examine the results, Edwards and her collaborators find that the toppling of ice cliffs is not necessary to reproduce past warm periods after all.

They also present lower sea level rise possibilities from Antarctica in this century. If they're right, the worst case is back down to about 40 centimeters, or a little over a foot, rather than three to four feet.

"Things may not be as absolutely terrible as that last study predicted," Edwards said. "But they're still bad."

It is a new science, she said, and without more modeling it's unclear how ice cliffs will ultimately affect sea level rise.

But then what happened in the Eemian? Edwards thinks it just took a long time to lose West Antarctica. That it wasn't fast. After all, the entire geologic period was thousands of years long.

"We're an impatient lot, humans, and the ice sheets don't respond in a decade, they're slow beasts," she said.

DeConto says he's learned something from the critique.

"The Edwards study does illustrate the need for more in-depth statistics than we originally applied to our 2016 model output, but the models are evolving rapidly and they have already changed considerably since 2016," he said in a written statement.

But he's not backing down on marine ice cliffs. The new critique, DeConto said, implies that "these processes aren't important for future sea level rise. And I think to me, that's kind of a dangerous message."

He certainly has his allies. Richard Alley, a well known glaciologist at Penn State University who has published with DeConto and Pollard, wrote in an email that "cliff retreat is not some strange and unexpected physical process; it is happening now in some places, has happened in the past, and is expected wherever sufficiently high temperatures occur in ocean or air around ice flowing into the ocean."

The Eemian - but worse?

There's one important thing to consider - the Eemian occurred without humans emitting lots of greenhouse gases.

Atmospheric carbon dioxide was far lower than it is today. The event was instead driven by changes in the Earth's orbit around the sun, leading to more sunlight falling on the northern hemisphere.

The big difference, this time around, is that humans are heating things up far faster than what is believed to have happened in the geologic past.

And that makes a key difference, said Ted Scambos, an Antarctic researcher who is leading the US side of an international multimillion dollar mission to study Thwaites Glacier, and who is a senior researcher at the National Snow and Ice Data Center in Colorado.

"The current pace of climate change is very fast," Scambos said, and the rate of warming might cause glaciers to behave differently than they did in the past.

Accordingly, Scambos says he sees the current debate as fruitful - "it's the discussion that needs to happen" - but that it doesn't lessen his worry about the fate of Thwaites Glacier if it retreats far enough.

"There's no model that says the glacier won't accelerate if it gets into those conditions," said Scambos. "It just has to."

Humans were nowhere near the Antarctic in the Eemian - and we have never, in the modern period, seen a glacier as big as Thwaites retreat. It's possible something is going to happen that we don't have any precedent or predictions for.

Just last week, for instance, scientists reported a large cavity opening beneath one part of the glacier - something they said models could not have predicted.

There is a massive stake involved now in at least trying to figure out what could happen - before it actually does. It will help determine whether humans, now organized and industrialized and masters of fossil fuels, are poised to drive a repeat of our own geological history.

2019 © The Washington Post

https://www.sciencealert.com/earth-s-climate-s-now-like-115-000-years-ago-when-the-sea-was-much-higher

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/

Dr. Mauri Pelto interviewed by Peter Sinclair on Antarctic melt, Part II

interview by Peter Sinclair, Weekend Wonk, May 18, 2014

Link:  http://climatecrocks.com/2014/05/18/the-weekend-wonk-dr-mauri-pelto-on-antarctic-melt-part-2/

Joe Romm: New Studies Suggest Many Coastal Cities Eventually To Be Abandoned With Antarctic Ice Collapse

by Joe Romm, Climate Progress, May 13, 2014

West Antarctica’s Thwaites glacier, one of a cluster that appear to have started irreversible collapse, threatening devastating sea level rise. Via NASA.

New studies in Science and Geophysical Research Letters (GRL) find that glaciers in the Amundsen Sea region of the great Antarctic ice sheet have begun the process of irreversible collapse. That by itself would raise sea levels 4 feet in the coming centuries.

But more importantly these glaciers act “as a linchpin on the rest of the [West Antarctic] ice sheet, which contains enough ice to cause” a total of 12 to 15 feet of global sea level rise, as the University of Washington news release for the Science study explains.

What most of the media has failed to emphasize is that (1) this is not a worst-case scenario and (2) failure to curb carbon pollution ASAP will result in vastly higher levels of sea level rise that devastate the world’s coastlines.

NASA’s Eric Rignot, lead author of the GRL study, explains the basic scientific findings in this video:

The New York Times story on the studies warns:

[Climatologist Richard Alley] added that while a large rise of the sea may now be inevitable from West Antarctica, continued release of greenhouse gases will almost certainly make the situation worse. The heat-trapping gases could destabilize other parts of Antarctica as well as the Greenland ice sheet, potentially causing enough sea-level rise that many of the world’s coastal cities would eventually have to be abandoned.

“If we have indeed lit the fuse on West Antarctica, it’s very hard to imagine putting the fuse out,” Dr. Alley said. “But there’s a bunch more fuses, and there’s a bunch more matches, and we have a decision now: Do we light those?”

But for some reason the New York Times buries these bombshells at the very end of a long piece. Even more inexplicably, the Times changed its online headline for the story from

to an indefensibly lamer one:

That new headline cuts out the heart of the news. It could have been used in stories about literally dozens of studies in the past quarter century. Heck, the New York Times headline in 1981 (!) for a NASA study led by James Hansen was … wait for it … “STUDY FINDS WARMING TREND THAT COULD RAISE SEA LEVELS.”

Apparently somebody associated with the Times thought the headline and lede were too strong, that “collapse” is somehow an inappropriate word that needed to be excised.

But it wasn’t. The headline of the news release from NASA and UC-Irvine (for the GRL study) was:

NASA-UCI Study Indicates Loss of West Antarctic Glaciers Appears Unstoppable

The Science study is titled, “Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica.” The headline from the news release is:

West Antarctic Ice Sheet collapse is under way

So the original NY Times story was accurate: the revised version, less so.

I asked Rignot for his thoughts on whether his study (along with the other) means we should revise the upper estimate for sea level rise this century (and beyond) if we stay on our current emissions path, which will take us to 4 °C (7 °F) warming or more by 2100. He replied:

I think that the minimum will be the upper end of the IPCC projections (90 cm) by 2100 and the maximum is hard to figure out but will likely exceed 1.2–1.4 meters.

The systems we are looking at do not respond to climate forcing in a smooth way, they start slow and then they proceed faster and faster. I am not convinced the numerical models are there yet, they are still conservative and do not include all the feedbacks, they are getting better than IPCC-class models but still trailing reality quite a bit.

After 2100, it will be several meters from the ice sheets, there is no red button to stop that. I surely hope that by then humanity will have reacted and slowed down the warming. I do not think we want to experience how fast Antarctica could fall apart if we push it hard … as we do now.

So the upper end of sea level rise will likely exceed 48 to 56 inches! That would not leave “southeastern Florida having many people at the end of this century,” to quote Hal Wanless, chair of the geological sciences department at University of Miami, from a 2013 interview.

The fact that these models do not include all the feedbacks and are conservative is a key point missed by much of the media. The Science article’s abstract concludes, “Less certain is the time scale, with the onset of rapid (>1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.”

The article itself points out:

An important feature of our numerical simulations is that they reveal a strong sensitivity to mechanical and/or rheological weakening of the margins, which can accelerate the rate of collapse by decades to centuries. Thus, future models will require careful treatment of shear margins to accurately project sea-level rise. Our simulations also assume that there is no retreat of the ice-shelf front. Full or partial ice-shelf collapse should produce more rapid retreat than we have simulated. In addition, we have not modeled ocean-driven melt that extends immediately upstream of the grounding line, which could also accelerate retreat.

Of course we know from a 2012 Nature study that Antarctica is melting from below, which “may already have triggered a period of unstable glacier retreat.”

The new Science study (Joughin et al.) also notes:

Our simulations are not coupled to a global climate model to provide forcing nor do they include an ice-shelf cavity-circulation model to derive melt rates…. As such, our simulations do not constitute a projection of future sea level in response to projected climate forcing.

Again, things could go faster and be much worse than this study suggests — as shown by Nature’s bombshell study on observations pointing to 10 °F warming by 2100.

Also, the West Antarctic Ice Sheet (WAIS) is only one contributor to sea level rise. We know Greenland’s ice melt is up nearly 5-fold since the mid-1990s, as we reported in late 2012. And parts of the East Antarctic Ice Sheet are not stable either — and have points of no return, as we reported earlier this month.

That was a point Dr. Alley made to me:

Joughin et al. didn’t run a worst-case scenario, as they state. So, it is possible that a worst-case version would shift the time of rapid retreat forward into this century. I don’t think we know yet, and I think that there is plenty of science to do, incorporating the new Rignot et al. data, and other measurements and ideas that many groups including Penn State have been working on.

And, maybe most important, if we have committed to 3 m or so of globally averaged sea-level rise from West Antarctica, even if delayed by many centuries, the costs are sobering, but are not as high as the costs of also committing to loss of Greenland’s ice and parts of East Antarctica’s ice as well. And, while some additional shrinkage of Greenland probably is already committed, major loss in Greenland and East Antarctica is not guaranteed yet. Too much warming is expected to cause major loss, with Greenland not too many degrees away and East Antarctica more uncertain. But, even with such a sobering possibility on the table, the costs are likely to rise faster than the temperature, so that each degree of warming costs more than the previous degree, and adding Greenland’s ice or parts of East Antarctica’s ice to the marine parts of West Antarctica would raise the costs a lot more.

In short, the fact that we may be stuck with 10 feet of sea level rise from WAIS over the next 200 to 900 years or so doesn’t mean we should stay on a CO2 emissions path that would (1) make it far more likely WAIS collapses sooner rather than later and (2) guarantees accelerated melting and/or collapse of large parts of Greenland and EAIS, too, leading to many tens of feet of sea level rise, and ultimately loss of virtually all land-based ice — raising seas over 200 feet.

The fact that such an unimaginable catastrophe would probably take many, many centuries to occur does not make it any less immoral for us — if we are the ones who make that outcome unstoppable.

I’ll end with the comments sent to me by sea-level-rise expert Stefan Rahmstorf, Co-Chair of Earth Systems Analysis, Potsdam Institute for Climate Impact Research:

What climate scientists have feared for decades is now beginning to come true: We are pushing the climate system across dangerous tipping points. Beyond such points, things like ice sheet collapse become self-sustaining and unstoppable, committing our children and children’s children to massive problems. The new studies strongly suggest the first of these tipping points has already been crossed. More tipping points lie ahead of us. I think we should try hard to avoid crossing them.

http://thinkprogress.org/climate/2014/05/13/3437033/coastal-cities-abandoned/

"Marine ice sheet collapse potentially underway for the Thwaites Glacier Basin, West Antarctica," by Ian Joughin et al., ScienceExpress

ScienceExpress, May 12, 2014

"Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011," by Eric Rignot et al., doi: 10.1002/2014GL060140

Geophysical Research Letters, (2014) in press; doi: 10.1002/2014GL060140

Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011

E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, and B. Scheuchl

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. 

Abstract 

We measure the grounding line retreat of glaciers draining the Amundsen Sea Embayment of West Antarctica using Earth Remote Sensing (ERS-1/2) satellite radar interferometry from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005-2009 when the glacier un-grounded from its ice plain. Thwaites Glacier retreated 14 km along its fast-flow core and 1-9 km along the sides. Haynes Glacier retreated 10 km along its flanks. Smith/Kohler glaciers retreated the most, 35 km along its ice plain, and its ice shelf pinning points are vanishing. These rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique (MC) that removes residual ambiguities from prior mappings. Upstream of the 2011 grounding line positions, we find no major bed obstacle that would prevent the glaciers from further retreat and draw down [of] the entire basin.

Peter Sinclair: Antarctic Ice Loss Accelerating (also Greenland)

by Peter Sinclair, Climate Denial Crock of the Week, March 29, 2014


Above, NASA video discussing increased mass loss from Pine Island Glacier, the soft underbelly of the West Antarctic ice sheet.

More evidence that the Antarctic Sheet is waking up.

WASHINGTON, D.C. — Six massive glaciers in West Antarctica are moving faster than they did 40 years ago, causing more ice to discharge into the ocean and global sea level to rise, according to new research.

The amount of ice draining collectively from those half-dozen glaciers increased by 77 percent from 1973 to 2013, scientists report this month in Geophysical Research Letters, a journal of the American Geophysical Union. Pine Island Glacier, the most active of the studied glaciers, has accelerated by 75% in 40 years, according to the paper. Thwaites Glacier, the widest glacier, started to accelerate in 2006, following a decade of stability.

Here, video from December with several scientist’s views on accelerating ice sheets, and what the Earth’s history says about ice.

 

The study is the first to look at the ice coming off the six most active West Antarctic glaciers over such an extended time period, said Jeremie Mouginot, a glaciologist at University of California-Irvine (UC-Irvine) who co-authored the paper. Almost 10% of the world’s sea-level rise per year comes from just these six glaciers, he said.

“What we found was a sustained increase in ice discharge—which has a significant impact on sea level rise,” he said.
The researchers studied the Pine Island, Thwaites, Haynes, Smith, Pope and Kohler glaciers, all of which discharge ice into a vast bay known as the Amundsen Sea Embayment in West Antarctica.

Below left, A satellite image of Pine Island Glacier shows an 18-mile-long crack across the glacier. 

Researchers used cracks and other physical features on the glaciers to calculate glacier acceleration by comparing image data from year to year to see how far the cracks traveled.

American Geophysical Union continued:
The amount of ice released by these six glaciers each year is comparable to the amount of ice draining from the entire Greenland Ice Sheet annually, Mouginot said. If melted completely, the glaciers’ disappearance would raise sea levels another 1.2 meters (four feet), according to co-author and UC-Irvine Professor Eric Rignot.

The decades of increasing speeds and ice loss are “a strong indication of a major, long-term leakage of ice into the ocean from that sector of Antarctica,” noted Rignot.

“This region is considered the potential leak point for Antarctica because of the low seabed. The only thing holding it in is the ice shelf,” said Robert Thomas, a glaciologist at the NASA Wallops Flight Facility, in Wallops Island, Va., who was not involved in the study. Ice shelves are platforms of permanent floating ice that form where glaciers meet the sea. In West Antarctica, ice shelves prevent the glaciers investigated in the study from slipping more rapidly into the ocean.

Mouginot and his colleagues used satellite data to look at sequential images of the glaciers from 1973 to 2013. The scientists then calculated how fast the ice was moving by tracking surface features, such as cracks in the ice, to determine the distance the glaciers traveled from month to month and year to year.

While the study considered the six glaciers collectively, it also revealed unprecedented change on the individual glacier level. Thwaites Glacier, the largest of the six with a width of 120 kilometers (75 miles), experienced a decade of near-stability until 2006, when its speed picked up by 0.8 kilometers (half a mile) per year – a 33 percent increase in speed, according to the study. This is the first time that such changes on Thwaites Glacier have been observed, said Mouginot.

Of all the glaciers in the study, Pine Island Glacier accelerated the most since 1973, increasing by 1.7 kilometers (one mile), per year. That’s a 75% increase in speed from approximately 2.5 kilometers (1.5 miles) per year in 1973 to 4 kilometers (2.5 miles) per year in 2013.

Both Pine Island and Thwaites glaciers contribute the most to overall ice discharge—about three-fourths of the total amount documented in the study. However, scientists also documented even higher rates of increased discharge in some of the smaller glaciers. Smith and Pope Glaciers nearly tripled the amount of ice they drained into the ocean since 1973.

The research team also found that the Pine Island Glacier is accelerating along its entire drainage system—up to 230 kilometers (155 miles) inland from where it meets the ocean.

“This paper is important in showing that a glacier can actually ‘feel’ what is happening far downstream of itself,” said Thomas. “It means that if you disturb the ice sheet near the coast, the glaciers will feel the push and rapidly respond hundreds of kilometers inland.”

This finding suggests that glacier acceleration models may need to be reevaluated, Thomas added. Most current models only take into account isolated speed changes resulting from a local disturbance, rather than representing how these changes affect the glacier as a whole.

http://climatecrocks.com/2014/03/28/antarctic-ice-loss-accelerating/