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Nature: Antarctica Is Melting From Below, Which ‘May Already Have Triggered A Period of Unstable Glacier Retreat’

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"Nature: Antarctica Is Melting From Below, Which ‘May Already Have Triggered A Period of Unstable Glacier Retreat’"

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We knew that “deep ocean heat is rapidly melting Antarctic ice.” And we knew that these warm ocean currents melting Antarctica were so intense that, seawater appears to “boil on the surface like a kettle on the stove.”

We also knew that the the West Antarctic ice sheet (WAIS) is inherently far less stable than the Greenland ice sheet because most of it is grounded far below sea level (see below). And JPL has told us that polar ice sheet mass loss is speeding up and is on pace for 1 foot sea level rise by 2050.

Now a new study using NASA satellite data finds the WAIS in particular is “being eaten away from below by warm water” as the AP put it, which “suggests that future sea levels could rise faster than many scientists have been predicting.”

The Nature study itself, “Antarctic ice-sheet loss driven by basal melting of ice shelves,” concludes:

We find that ocean-driven ice-shelf thinning is in all cases coupled with dynamic thinning of grounded tributary glaciers that together account for about 40% of Antarctic discharge and the majority of Antarctic ice-sheet mass loss. In agreement with recent model predictions, we conclude that it is reduced buttressing from the thinning ice shelves that is driving glacier acceleration and dynamic thinning. This implies that the most profound contemporary changes to the ice sheets and their contribution to sea level rise can be attributed to ocean thermal forcing that is sustained over decades and may already have triggered a period of unstable glacier retreat.

This ought to be doubly worrisome since scientists told us in October that the Greenland Ice Sheet “could undergo a self-amplifying cycle of melting and warming … difficult to halt.”

The new study is behind a firewall, so I’m excerpting the NASA news release below along with a NASA video.

Warm Ocean Currents Cause Majority of Ice Loss from Antarctica

Cross-posted from NASA

Warm ocean currents attacking the underside of ice shelves are the dominant cause of recent ice loss from Antarctica, a new study using measurements from NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) revealed.

This animation shows the circulation of ocean currents around the western Antarctic ice shelves. The shelves are indicated by the rainbow color; red is thicker (greater than 550 meters), while blue is thinner (less than 200 meters). Credit: NASA/Goddard CGI Lab

An international team of scientists used a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves: warm ocean currents thawing the underbelly of the floating extensions of ice sheets and warm air melting them from above. The finding, published today in the journal Nature, brings scientists a step closer to providing reliable projections of future sea level rise.

The researchers concluded that 20 of the 54 ice shelves studied are being melted by warm ocean currents. Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise. This ocean-driven thinning is responsible for the most widespread and rapid ice losses in West Antarctica, and for the majority of Antarctic ice sheet loss during the study period.

“We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt,” said the study’s lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom. “The oceans can do all the work from below.”

To map the changing thickness of almost all the floating ice shelves around Antarctica, the team used a time series of 4.5 million surface height measurements taken by a laser instrument mounted on ICESat from October 2003 to October 2008. They measured how the ice shelf height changed over time and ran computer models to discard changes in ice thickness because of natural snow accumulation and compaction. The researchers also used a tide model that eliminated height changes caused by tides raising and lowering the ice shelves.

“This study demonstrates the power of space-based, laser altimetry for understanding Earth processes,” said Tom Wagner, cryosphere program scientist at NASA Headquarters in Washington.” Coupled with NASA’s portfolio of other ice sheet research using data from our GRACE mission, satellite radars and aircraft, we get a comprehensive view of ice sheet change that improves estimates of sea level rise.”

Previous studies used satellite radar data to measure the evolution of ice shelves and glaciers, but laser measurements are more precise in detecting changes in ice shelf thickness through time. This is especially true in coastal areas. Steeper slopes at the grounding line, where floating ice shelves connect with the landmass, cause problems for lower-resolution radar altimeters….

The new research also links the observed increase in melting that occurs on the underside of a glacier or ice shelf, called basal melt, and glacier acceleration with changes in wind patterns.

“Studies have shown Antarctic winds have changed because of changes in climate,” Pritchard said. “This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”

JR: As I wrote in the “high water” part of my book, the WAIS is inherently less stable:

Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study inScience examined the underwater grounding lines-the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature.

The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS (see, for instance, here).

Did I mention the time to act is now?

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18 Responses to Nature: Antarctica Is Melting From Below, Which ‘May Already Have Triggered A Period of Unstable Glacier Retreat’

  1. Mauri Pelto says:

    The key here is that the thinning that has led to destabilization of the thinnest ice shelves along the Ant. Peninsula are now evident around much of the WAIS. Smith Glacier is another example. That this is being driven by warming oceans, where most of the heat has gone to date. Thin ice shelves tend to have more extensive rifting which can lead to enhanced calving. The thinner shelves also are have a reduced connection to potential pinning points that act as a buttress. This reduced friction leads to more rapid flow, which further enhances rifting.

  2. Lou Grinzo says:

    Yet another example of how we keep discovering evidence that the entire Earth System is far less robust (in the engineering/systems sense of immunity to outside shocks) than we thought. Albedo flip, Amazon forest dryout, ice sheet and glacier dynamics, methane hydrate and permafrost emissions — increasingly it feels like the entire biosphere was finely balanced, able to shrug off or recover from minor jostles, but susceptible to something much more persistent, like our dumping CO2 into the atmosphere at astonishing rates for over 200 years.

    On the bright side, at least all that CO2 won’t hang around long after we finally stop pouring it into the air, right? Right? Why did everyone get so quiet in here all of a sudden…?

    • M Tucker says:

      Lou I would respectfully disagree. Earth has been shocked in the past and has recovered each time but some of these shocks have caused dramatic changes and the recovery time can be long on human time scales. However nothing in the past really compares with the massive volume of GHG we humans have managed to pump into the atmosphere over such a short time frame geologically speaking. If we ignore the Permian extinction and stick with more recent events it can be shown that Earth, and the majority of the species living on her, has done pretty well at absorbing GHG shocks.

      I recently discovered these tidbits:

      For the Cretaceous Hothouse event the rate of warming was about 2.5×10^-5 per 100 years. It lasted about 30 million years and warmed the planet by an average of about 5 degrees Celsius.

      For the PETM event the rate of warming was about 2.5×10^-2 per 100 years. It lasted about 200,000 years and warmed the planet by an average of about 5 degrees Celsius.

      For the Cretaceous no significant extinctions resulted. For the PETM the deep ocean acidified and some marine life went extinct but life on land survived. Pretty robust! PETM warmed 1000 times faster than the hothouse event but most of life survived.

      But today we are warming Earth at about 5 orders of magnitude greater than during the Cretaceous. So we are pushing the limit and life will suffer…including us.

      I got those bits of info from a paper by Dr Lee R Kump, professor of geosciences at Penn St University and coauthor of Dire Predictions with Dr Michael Mann. He worked with a team of scientists to, in part, determine the PETM rate of warming and is considered an expert on “planetary fevers.”

      • colinc says:

        For the Cretaceous no significant extinctions resulted. For the PETM the deep ocean acidified and some marine life went extinct but life on land survived. Pretty robust! PETM warmed 1000 times faster than the hothouse event but most of life survived.

        Now, the climate is warming 50 to 1,000 times faster than the PETM (depending on source) and, let’s not forget that those earlier lifeforms did not possess countless toxin-spewing chemical processing facilities, all “disasters” just waiting to happen, and, oh yeah, enough nuclear/biological weapons to wipe-out all life on the planet several times over.

    • Mulga Mumblebrain says:

      The earth-system does appear to be robust, but, once collapsing, the process will be rapid, as various synergies kick in, and irreversible. I’ve seen a description of an observation made by Seneca, the Roman, two thousand years ago, along similar lines, that various great edifices take time and much effort to build up, but, when they collapse, the process is comparatively rapid. Having seen a truly sobering report on ABC’s Catalyst science program this week, on the global extent and intensity of tree death, one gets the increasing sense that we are already well on the way down the slippery slide to catastrophe. And still the political and economic system proves itself unable to act.

      • Gail Zawacki says:

        Yes, I agree things are going to collapse rather more quickly than most predictions indicate. This morning I had put a link to that program with some comments about its annoying flaws here:

        http://witsendnj.blogspot.com/2012/04/expect-us.html

        before I took the train to New York, to sneak around the barricades and get arrested with some other Occupiers, lying down on the sidewalk directly across from the Stock Exchange with my sign “Industrial Civilization = Ecopocalypse”.

        While we were waiting in the paddy wagon a fellow handcuffed prisoner wiggled his smartphone out from his back pocket long enough for us to see we received the good revolutionizing seal of approval from the Yes Men, yay!

    • Merrelyn Emery says:

      Yes Lou, the Earth keeps proving that she is indeed a system, not a collection of linear forces that may ‘interact’ as assumed by our predominantly linear mechanistic sciences. That is why she is always outrunning the predictions.

      That is also why the recent criticism of Lovelock (and Margulis), on CP, for not following the ‘science’ was akin to criticizing Galileo for not following the Catholic Church, ME

    • Wonhyo says:

      Yet another example of how we keep discovering evidence that the entire Earth System is far less robust (in the engineering/systems sense of immunity to outside shocks) than we thought.

      This characterization is unfair to the Earth. The fact that the global ecosystem has endured industrial impacts as long as it has is a testament to its robustness. We’re simply pushing it beyond its limits.

      Consider that the Earth has recovered from atmospheric CO2 concentrations as low as 180 ppm and as high as 300 ppm over the last 800,000 years. Human GHG emissions pushed the concentration beyond 300 pm back in the 1940s or 1950s.

      The cumulative effect of 150 years of increasing human CO2 emissions is simply pushing the global ecosystem beyond its limits. The global ecosystem has been remarkably robust. The human propensity to grow, consume, and pollute has been even more robust.

      • ianam says:

        “This characterization is unfair to the Earth.”

        Lou’s characterization wasn’t so much of the Earth as it was of us. I find most of these responses to be straining to miss his point and find disagreement where there really isn’t any.

  3. NJP1 says:

    the ice sheet problem, and all the rest of what’s going on in the world, fits neatly with the obvious conclusion that humanity has become a plague species that has overrun its host body. that body is reacting to get rid of us, a climate change sneeze in reaction to what has become a global fever

    • Mulga Mumblebrain says:

      It’s not that humanity has become a plague, but certain cells, certain individuals, have turned entirely malignant, and due to some innate advantage that they possess or have acquired, they have taken over humanity and are driving it to imminent self-destruction. I sometimes think it is a little like the fungi that infect ants’ brains, and somehow impel them to climb to the top of branches, where the fungal spores, once the ant has been reduced to a fungi filled husk, can better spread. Or perhaps the ‘Invasion of the Body-Snatchers’ is even better as an analogy. Humanity is dominated by its greediest, most violent, most arrogant, least empathic, most unscrupulous individuals, and has been as far as I can tell, for millennia. These are the Right, that fraction of humanity whose basic drive is fear and hatred of others, and their dominance simply had to lead to human self-destruction at some time, which is soon, and by some mechanism, which appears to be ecological destabilisation leading to starvation, disease and war.

  4. Mark E says:

    And all of this effects water temps in the depths of the deep ocean basins in the world, since a lot of that very cold water gets its start off the Antarctic coastline. I don’t think we’ve got a very good grip on the processes to allow for modeling yet, but gotta wonder how the rest of the ocean system is reacting to a decrease flow of very-cold-bottom water.

    http://www.noaanews.noaa.gov/stories2012/20120320_antarcticbottomwater.html

    • Mulga Mumblebrain says:

      Not well, one would surmise.

    • Sasparilla says:

      With Earth’s past periodic history of anoxic ocean(s) conditions (theorized to start with reduced or stopped levels of oxygen rich cold water flowing to the bottom – and warmer flows instead), that is not a reassuring change for the Antarctic (I believe its already known the cold water diving down in the Arctic has been slowing in volume over the past decades).

      Guessing this would happen on a longer time scale, but with the way things are happening…and once the deep ocean flows changes to warm water or stops it would seem bloody difficult to “fix” that.

  5. Rabid Doomsayer says:

    We continue to change forcing sixty times faster than anything in the paleoclimatic record, and expect changes slower and less devastating.

    We continue to assume the biosphere will absorb half of our emissions. But look at the evidence, loss of phytoplankton, tree deaths, wild fires and the paleo record that shows the biosphere becomes a source rather than a sink as temperatures rise.

    We have awakend the tiger and need to grab hold of it’s tale. But no, we want to keep poking.

  6. Sasparilla says:

    Excellent article showing news we need to be aware of.

    We’re really messing with the ocean flows and they have changed in the past (stopping or going from cold oxygen rich ocean depth currents to warm diving water turning parts of oceans and entire oceans anoxic as a result (long time period) – anoxic means little or no oxygen (the organisms that thrive in this environment emit hydrogen sulfide gas, a poison to most oxygen based life, as a byproduct if memory serves). Under a Green Sky is a good book on the past history if anyone is curious.

    While we think we can fix alot of stuff in the atmosphere still, I have a gut feeling we should tread very lightly with the ocean currents as they just don’t seem to be as amendable to human meddling for quick fixes after being forced to change – I sure hope we get our heads out of our status quo in time.

    As Joe says every time, the time to act is now.

  7. Tim Palmer says:

    Yes, the rate of warming is already many times more rapid than typical warming events of the past. Even more unusual is the way that acceleration is being achieved. In the past the relatively regular and cyclic warming phases were initiated gently by combinations of axial tilt and orbital shape. As a result of these small forcings, ice retreated globally, reducing albedo and increasing the warming a bit more quickly. Eventually warming reached the point where CO2 began to evolve out of the oceans as they warmed and out of the permafrost as it thawed. The thermal ‘thickening’ of the infrared retaining blanket of atmosphere, a result of rising CO2, pushed the temperature somewhat higher still. In the case of an event like the PETM, it appears that the thawing penetrated the stores of methane ice slumbering on the continental shelves. As the methane fizzed up through the water column, there was mixing of warmer surface waters to greater depths, creating yet another positive feedback loop and a real spike of atmospheric CO2 resulted. The event that is evolving now in real time has almost instantaneously skipped the first half dozen or so steps of the previous events we are aware of. The release of CO2 via our burning of fossil fuels is actually jump-starting the process right up to the point where the methane hydrates were released in those previous events. Release of the methane in the clathrates was the crescendo in an event like the PETM. However, those gigatons of CO2 in the methane hydrates have not yet been released. If we can not/do not begin to immediately ameliorate our CO2 evolving behaviors then the release of CO2 from the sea floor and permafrost seems likely to produce a sudden atmospheric crescendo– the grand finale of an amazing Bio/Geological epoch! Unfortunately, it has every prospect of being the shortest epoch ever seen on this planet–the Anthropocene.

  8. Disgusted American says:

    well I wouldnt want to be born in 2012 – can u imagine what 2050, 2070 will be like? No Thanks – I’ll have been long gone – I was born in 1960 …2035-40 is plenty of time for me..then Im outa here….