West Antarctic Ice Sheet News

You may have heard the news: two teams of scientists claiming that the West Antarctic Ice Sheet has been irreversibly destablized, leading to a slow-motion process that in some number of centuries will cause 3 meters of sea level rise.

“Today we present observational evidence that a large section of the West Antarctic Ice Sheet has gone into irreversible retreat,” an author of one of the papers, Eric Rignot, a glaciologist at NASA’s Jet Propulsion Laboratory, said at a news conference recently. “It has passed the point of no return.”

A little context might help.

The West Antarctic Ice Sheet is the ice sheet that covers Antarctica on the Western Hemisphere side of the Transantarctic Mountains. The bed of this ice sheet lies well below sea level. The ice gradually flows into floating ice shelves such as the Ross Ice Shelf and Ronne Ice Shelf, and also glaciers that dump ice into the Amundsen Sea. Click on the map to make it bigger, so you can see all these features.

The West Antarctic Ice Sheet contains about 2.2 million cubic kilometers of ice, enough to raise the world’s oceans about 4.8 meters if it all melted. To get a sense of how big it is, let’s visit a crack in one of its outlet glaciers.

In 2011, scientists working in Antarctica discovered a massive crack across the Pine Island Glacier, a major glacier in the West Antarctic Ice Sheet. The crack was 30 kilometers long, 80 meters wide and 60 meters deep. The pictures above and below show this crack—the top one is from NASA, the bottom one was taken by an explorer named Forrest McCarthy.

By July 2013, the crack expanded to the point where a slab of ice 720 square kilometers in size broke off and moved into the Amundsen Sea.

However, this event is not the news! The news is about what’s happening at the bottom of the glaciers of the West Antarctic Ice Sheet.

The West Antarctic Ice Sheet sits in a bowl-shaped depression in the earth, with the bottom of the ice below sea level. Warm ocean water is causing the ice sitting along the rim of the bowl to thin and retreat. As the edge of the ice moves away from the rim and enters deeper water, it can retreat faster.

So, there could be a kind of tipping point, where the West Antarctic Ice Sheet melts faster and faster as its bottom becomes exposed to more water. Scientists have been concerned about this for decades. But now two teams of scientists claim that tipping point has been passed.

Here’s a video that illustrates the process:

And here’s a long quote from a short ‘news and analysis’ article by Thomas Sumner in the 16 May 2014 issue of Science:

A disaster may be unfolding—in slow motion. Earlier this week, two teams of scientists reported that Thwaites Glacier, a keystone holding the massive West Antarctic Ice Sheet together, is starting to collapse. In the long run, they say, the entire ice sheet is doomed. Its meltwater would raise sea levels by more than 3 meters.

One team combined data on the recent retreat of the 182,000-square-kilometer Thwaites Glacier with a model of the glacier’s dynamics to forecast its future. In a paper on page 735, they report that in as few as 2 centuries Thwaites Glacier’s edge will recede past an underwater ridge now stalling its retreat. Their models suggest that the glacier will then cascade into rapid collapse. The second team, writing in Geophysical Research Letters, describes recent radar mapping of West Antarctica’s glaciers and confirms that the 600-meter-deep ridge is the final obstacle before the bedrock underlying the glacier dips into a deep basin.

Because inland basins connect Thwaites Glacier to other major glaciers in the region, both research teams say its collapse would flood West Antarctica with seawater, prompting a near-complete loss of ice in the area over hundreds of years.

“The next stable state for the West Antarctic Ice Sheet might be no ice sheet at all,” says the Science paper’s lead author, glaciologist Ian Joughin of the University of Washington, Seattle. “Very crudely, we are now committed to global sea level rise equivalent to a permanent Hurricane Sandy storm surge,” says glaciologist Richard Alley of Pennsylvania State University, University Park, referring to the storm that ravaged the Caribbean and the U.S. East Coast in 2012. Alley was not involved in either study.

Where Thwaites Glacier meets the Amundsen Sea, deep warm water burrows under the ice sheet’s base, forming an ice shelf from which icebergs break off. When melt and iceberg creation outpace fresh snowfall farther inland, the glacier shrinks. According to the radar mapping released this week in Geophysical Research Letters from the European Remote Sensing satellite, from 1992 to 2011 Thwaites Glacier retreated 14 kilometers. “Nowhere else in Antarctica is changing this fast,” says University of Washington Seattle glaciologist Benjamin Smith, co-author of the Science paper.

To forecast Thwaites Glacier’s fate, the team plugged satellite and aircraft radar maps of the glacier’s ice and underlying bedrock into a computer model. In simulations that assumed various melting trends, the model accurately reproduced recent ice-loss measurements and churned out a disturbing result: In all but the most conservative melt scenarios, a glacial collapse has already started. In 200 to 500 years, once the glacier’s “grounding line”—the point at which the ice begins to float—retreats past the ridge, the glacier’s face will become taller and, like a tower of blocks, more prone to collapse. The retreat will then accelerate to more than 5 kilometers per year, the team says. “On a glacial timescale, 200 to 500 years is the blink of an eye,” Joughin says.

And once Thwaites is gone, the rest of West Antarctica would be at risk.

Eric Rignot, a climate scientist at the University of California, Irvine, and the lead author of the GRL study, is skeptical of Joughin’s timeline because the computer model used estimates of future melting rates instead of calculations based on physical processes such as changing sea temperatures. “These simulations ought to go to the next stage and include realistic ocean forcing,” he says. If they do, he says, they might predict an even more rapid retreat.

I haven’t had time to carefully read the relevant papers, which are these:

• Eric Rignot, J. Mouginot, M. Morlighem, H. Seroussi and B. Scheuchl, Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011, Geophysical Research Letters, accepted 12 May 2014.

• Ian Joughin, Benjamin E. Smith and Brooke Medley, Marine ice sheet collapse potentially underway for the Thwaites glacier basin, West Antarctica, Science, 344 (2014), 735–738.

I would like to say something more detailed about them someday.

The paper by Eric Rignot et al. is freely available—just click on the title. Unfortunately, you can’t read the other paper unless you have a journal subscription. Sumner’s article which I quoted is also not freely available. I wish scientists and the journal Science took more seriously their duty to make important research available to the public.

Here’s a video that shows Pine Island Glacier, Thwaites Glacier and some other nearby glaciers:

14 Responses to West Antarctic Ice Sheet News

  1. The Rignot article appears to be freely available online.

  2. gamanrad says:

    In my experience, writing to the authors often results in receipt of a copy of the paper in question. Yes, they should be more widely disseminated, but many journals are a ‘for profit’ industry. The other thing is, while this is a huge and unprecedented event, the timescale for this disaster’s unfolding is, in terms of human life, slow. If there was sufficient response now, considerable adaptation could take place and this would mitigate many of the impacts, both for humans and, if we were really thoughtful, for other biophysical systems. Thanks, as ever, for your very useful work (and you probably already know the above).

    • John Baez says:

      I’ve edited my blog article, adding a lot of new material and removing the grumpy comment that may have prompted your reply. Check out the new pictures and such!

  3. Freely available or not, there is material from a news conference at NASA about this, at http://www.nasa.gov/jpl/earth/antarctica-telecon20140512/#.U3dq7PldV8E.

    But, I think, better, is a talk by Professor Richard Alley doing an update on the state of the climate last summer at the AGU Chapman Conference. The link is https://www.youtube.com/watch?v=Z_-8u86R3Yc. He covers a lot of stuff and is an expert on many things, but, as a specialist on ice and glaciology, really shines there. It is good to hear the ice story in context.

    At 29:30 he begins to talk about Greenland and ice.

    At 32:10 he begins to talk about Antarctica.

    At 36:30 he begins to talk about the WAIS, the PIG, and so on, speaking from a context before the current findings were known.

    Incidently, earlier in the talk, at 26:27, Professor Alley speaks about the great Permian extinction, something which Dr Neil de Grasse Tyson highlighted in the *Cosmos* episode http://www.cosmosontv.com/watch/244543555624.

    BTW, I found that *Cosmos* episode profoundly disturbing … Moved me to tears. I tracked down what is apparently the definitive summary of it, Ogden and Sleep, “Explosive eruption of coal and basalt and the end-Permian mass extinction”, *PNAS*, 109(1), 2011, http://www.pnas.org/content/109/1/59.

    • John Baez says:

      Hypergeometric wrote:

      Freely available or not, there is material from a news conference at NASA about this…

      If you don’t have to pay or have a subscription, that’s what I call ‘freely available’. Thanks!

      BTW, I found that Cosmos episode profoundly disturbing … Moved me to tears. I tracked down what is apparently the definitive summary of it, Ogden and Sleep, “Explosive eruption of coal and basalt and the end-Permian mass extinction”, PNAS, 109 (1), 2011, http://www.pnas.org/content/109/1/59.

      Thanks again. I’ve been fascinated by the end-Permian extinction ever since I read this book:

      • Michael J. Benton, When Life Nearly Died: The Greatest Mass Extinction of All Time, Thames and Hudson, 2003.

      Before it happened, the seabeds near China looked something like this:

      After it happened, they looked like this:

      It took 10 million years for coral reefs to form again after this extinction… and it took 50 million years for biodiversity to fully recover. It was indeed a sad event. It would be sad in a different way if we caused a (probably much smaller) extinction event, since we’re conscious beings who sort of understand what we’re doing.

      • Indeed, it would probably be much smaller, even if we raised \text{CO}_{2} concentrations to an amount in excess of 1000 ppm quickly, simply because we don’t deposit the majority of it high in atmosphere as apparently the Siberian Traps were able to do, at least according to Ogden and Sleep.

  4. John Baez says:

    Here’s a helpful article:

    • Eric Rignot, Global warming: it’s a point of no return in West Antarctica. What happens next?, The Guardian, 17 May 2014.

    Last Monday, we hosted a NASA conference on the state of the West Antarctic ice sheet, which, it could be said, provoked something of a reaction. “This Is What a Holy Shit Moment for Global Warming Looks Like,” ran a headline in Mother Jones magazine.

    We announced that we had collected enough observations to conclude that the retreat of ice in the Amundsen sea sector of West Antarctica was unstoppable, with major consequences – it will mean that sea levels will rise one metre worldwide. What’s more, its disappearance will likely trigger the collapse of the rest of the West Antarctic ice sheet, which comes with a sea level rise of between three and five metres. Such an event will displace millions of people worldwide.

    Two centuries – if that is what it takes – may seem like a long time, but there is no red button to stop this process. Reversing the climate system to what it was in the 1970s seems unlikely; we can barely get a grip on emissions that have tripled since the Kyoto protocol, which was designed to hit reduction targets. Slowing down climate warming remains a good idea, however – the Antarctic system will at least take longer to get to this point.

    The Amundsen sea sector is almost as big as France. Six glaciers drain it. The two largest ones are Pine Island glacier (30km wide) and Thwaites glacier (100km wide). They stretch over 500km.

    Many impressive scientists have gone before us in this territory. The concept of West Antarctic instability goes back to the 1970s following surveys by Charles Bentley in the 1960s that revealed an ice sheet resting on a bed grounded well below sea level and deepening inland. Hans Weertman had shown in 1974 that a marine-based ice sheet resting on a retrograde bed was unstable. Robert Thomas extended his work to pursue the instability hypothesis. Terry Hughes suggested that the Pine Island sector of West Antarctica was its weak underbelly and that its retreat would collapse the West Antarctic ice sheet. Considerable uncertainty remained about the timescale, however, due to a lack of observation of this very remote area.

    Things changed with the launch of the ERS-1 satellite which allowed glaciers in this part of antartica to be observed from space. In 1997, I found that the grounding line (where the glacier detaches from its bed and becomes afloat) of Pine Island glacier had retreated five kilometres in the space of four years, between 1992 and 1996. Stan Jacobs and Adrian Jenkins had found a year earlier that the glacier was bathing in unusually warm waters, which suggested the ocean had a major influence on the glacier. Duncan Wingham and others showed that the glacier was thinning. In 2001, I found that Thwaites glacier was retreating too .

    At that point, the scientific community took a different look at the region. Work by the British Antarctic Survey, Nasa and Chile led to more detailed observations, a monitoring programme was initiated, instruments were placed on the ice, in the ocean and scientific results started to pile up from a variety of research programmes. From that point, we all sought to find out whether this was really happening. Now, two decades after this process started, we have witnessed glacier grounding lines retreat by kilometres every year, glaciers thinning by metres every year hundreds of kilometres inland, losing billions of tons of water annually, and speeding up several percent every year to the flanks of topographic divides.

    Thwaites glacier started to accelerate after 2006 and in 2011 we detected a huge retreat of the glacier grounding lines since 2000. Detailed reconstructions of the glacier bed further confirmed that no mountain or hill in the back of these glaciers could act as a barrier and hold them up; and 40 years of glacier flow evolution showed that the speed-up was a long story.

    All these results indicate a progressive collapse of this area. At the current rate, a large fraction of the basin will be gone in 200 years, but recent modelling studies indicate that the retreat rate will increase in the future. How did this happen? A clue is that all the glaciers reacted at the same time, which suggested a common force that can only be the ocean. Ocean heat is pushed by the westerly winds and the westerlies have changed around Antarctica in response to climate warming and the depletion of the ozone. The stronger winds are caused by a world warming faster than a cooling Antarctica. Stronger westerlies push more subsurface warm waters poleward to melt the glaciers, and push surface waters northward.

    Nerilie Abram and others have just confirmed that the westerlies are stronger now than at any other time in the past 1,000 years and their strengthening has been particularly prominent since the 1970s as a result of human-induced climate warming. Model predictions also show that the trend will continue in a warming climate.

    What this means is that we may be ultimately responsible for triggering the fast retreat of West Antarctica. This part of the continent was likely to retreat anyway, but we probably pushed it there faster. It remains difficult to put a timescale on it, because the computer models are not good enough yet, but it could be within a couple of centuries, as I noted. There is also a bigger picture than West Antarctica. The Amundsen sea sector is not the only vulnerable part of the continent. East Antarctica includes marine-based sectors that hold more ice. One of them, Totten glacier, holds the equivalent of seven metres of global sea level.

    Controlling climate warming may ultimately make a difference not only about how fast West Antarctic ice will melt to sea, but also whether other parts of Antarctica will take their turn. Several “candidates” are lined up, and we seem to have figured a way to push them out of equilibrium even before warming of air temperature is strong enough to melt snow and ice at the surface.

    Unabated climate warming of several degrees over the next century is likely to speed up the collapse of West Antarctica, but it could also trigger irreversible retreat of marine-based sectors of East Antarctica. Whether we should do something about it is simply a matter of common sense. And the time to act is now; Antarctica is not waiting for us.

  5. Uncle Al says:

    There is no reason to assume “slow.” Overburden release triggers temblors. Friction at the ground-ice interface is lubricative, Catastrophic flow is expected. We must emergency evacuate the Hamptons!

    • Well, it depends, and we don’t really know. I’m betting half of glaciologists are blowing their jets right now tuning up models to be able to produce a single graph: A three dimensional posterior probability density giving mass to rate of flow per month versus year out for the next 500 years. Glaciers are complicated mechanisms. Even with such a model, which would need to be simulated on one of the Big Guys (supercomputers), needing, at my last check, at least 50m by 50m resolution, there still needs to be fieldwork done to establish good initial conditions. There’s only so much that can be done from satellite and aircraft.

      I guess you could bound how fast these could go from what’s been seen elsewhere, like Alaska, and Greenland, per “Chasing Ice”.

  6. Paul Mackilligin says:

    The loss of the 2 million sq kilometre West Antarctic Ice Sheet is likely to have a further effect on global warming due to both a reduction in albedo and a release of trapped methane.

  7. lee bloomquist says:

    About 400 years ago Galileo got into trouble by putting knowledge on the table in a game with belief systems, and lost. Today most of us would agree that those belief systems were simultaneously driven by, and used as a primary tool, *fear*. Galileo really should have won, we think, if the game would have really been fair.

    400 years after the West Antarctica ice sheet disappears– in a complete surprise to almost everybody except people like us (we think)– what will be the consensus then? Somebody of that day and age will of course have to write a book about it, with a title something like–

    Galileo and the Failure to Deal with Climate Change: How Belief Systems Create Power, Maintain Ignorance and Destroy Knowledge

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