The Thermometer Series: The sixth of six articles on the next steps in climate reform and why we need to advance current climate change strategy.
New research has for the first time defined the tipping point between a stable WAIS and an Antarctica that collapses uncontrollably.
Potsdam Institute researchers (Levermann and Feldmann) tell us is that if we do not return our oceans to their preindustrial temperature by 2050, we will see out of control collapse of the WAIS and ultimately all of Antarctica. Their different scenarios all point to one critical issue: ocean warming. Four scenarios resulted in no collapse, all returning upper ocean warming to its preindustrial temperature by 2050. (1)
The critical part of this research deals with the time remaining until collapse, not how fast the collapse occurs. Traditional ice sheet collapse dynamics (modeling physics) are used and their collapse time frame is little different than what is supported by the consensus, or centuries to millennia.
Because of scant research and slow (10-year) integration of new research into IPCC consensus projections, IPCC modeling and thus, consensus projections, are based on simple melt and iceberg discharge relationships that have been observable in the historic record. This is why there is a huge discrepancy between IPCC sea level rise projections and actual observations of prehistoric evidence in the field. The IPCC does not come to a consensus about future sea level rise from physical evidence alone, modeling must be included that corroborates the evidence.
The IPCC caveats their sea level rise projections heavily with cautions that “dynamical collapse mechanisms” are not included. There is a great disparity between IPCC’s 4 mm per year worst-case sea level rise from Antarctica and evidence from Xcaret Reef 121,000 years ago of 36 mm per year, or the large body of science that shows rapid ice sheet collapse and sea level rise in prehistory of ten feet per century (30 mm per year) for centuries on end. (2) It is also worth noting that in the last five years, NOAA’s sea level rise data looks to have jumped from its 3 mm per year level to 5 mm per year or greater, but cautioned is advised with this interpretation because the Super El Nino. (3)
More new work includes Deconto and Pollard 2016 that breaks through the ice cube melt modeling barrier with work that has begun to approach ancient evidence of collapse. (4) They say three feet from Antarctica alone by 2100, which is nine times faster than the consensus opinion of the IPCC of four inches by 2100.
But actual evidence is many times faster than DeConto and Pollard and critically, the maximum sea level rise adaptation rate is 3 feet per century. (5) DeConto and Pollard have opened a new door that is fundamental to current climate reform strategy. Their methods use refined physics not yet modeled before that focus on lateral stress constraints, pinning, buttressing, and most fascinating, ice cliff collapse.
It seems that when an ice cliff becomes taller than about 300 feet, it does not have enough strength to hold itself up and collapses. This is an easily observable phenomenon if one can travel to the face of a marine terminating ice sheet or a glacier terminating on water. The ice cliffs in these areas are never higher than 200 to 300 feet.
In West Antarctica, where we have the only marine ice sheet remaining in the world, the ice sheet rises 6,000 feet above the level of the ocean 500 miles inland. The foot of the ice sheet lies on the ocean floor up to 5,000 feet below sea level and along its ocean edge for 1,000 miles along the Ross and Ronne ice shelves and places like the Amundsen Sea Embayment, the ice thins to a floating sheet that rises only 200 to 300 feet above the sea. With the onset of collapse however, with warnings coming from scientists since 2008 that collapse has begun (6), this will radically change.
Most of Antarctica is still far below freezing, but the oceans are warming, and particularly the upper oceans around Antarctica. Interestingly, increased sea ice in Antarctica, because of increased winds around Antarctica due to warming, is increasing upper ocean warming even more than atmospheric warming alone. (7)
The stronger winds caused by a warmer Earth blow young sea ice out to sea and new ice quickly forms. This increase in the area of sea ice coverage decreases ocean mixing from wind and keeps the ocean warm. Record Antarctic sea ice coverage is doing a lot of warming.
Warmer upper ocean water circulates beneath the floating shelf of the WAIS. The warm water has already melted the edge of the WAIS up above its sill, or its underwater pinning point. Think of this pinning point as a ridge that has been raised upwards because of the great weight of the Antarctic Ice Sheet. Like a giant medicine ball plopped down in a muddy field, the mud around its edges rises in a ridge around the medicine ball.
In our old climate, this ridge protruded up into the bottom of the floating ice sheet with water on both sides, holding back the flow of ice outward from the interior. Today’s warmer ocean has melted the bottom of WAIS up high enough so that it has lost contact with its pinning point. In some places outward flow has dramatically increased. (8) Just as important, warm ocean water is now flowing far back into the previously inaccessible reaches of the under-ice ocean.
At the most extreme measured so far, underice melt is in excess of 100 meters per year. This is triple the extreme surface melt in Greenland of 30 meters per year. (9)
According to the principal (DeConto,) their collapse estimate is likely conservative: “We are imposing a “speed limit” on the cliff collapse mechanism, that could indeed be conservative-especially for cliffs much taller than 100m (which will exist in some places as the ice margin retreats landward). For example, the retreat rate at the face of Jakobshavn glacier in Greenland is >10km/yr, and that’s up in a long fjord choked with ice- with limited communication with open ocean. These cliff margins in Antarctica would be much broader- and will not become as easily choked with melange/bergs. The rate of retreat in the model ensembles maxes out at around 3km/yr- much slower than Jakobshavn. With that said, we could be missing some important negative feedbacks in the rate of retreat (I hope we are). We still have a long way to go- in representing these physics in the models.” (10)
- West Antarctic Ice Sheet (WAIS) Collapse Tipping Point Defined… This work out of the German National Science Institute describes marine ice sheet collapse mechanisms, and how there is a very distinct tipping point with the West Antarctic Ice Sheet where collapse becomes irreversible in about 2050. The very important take-away from this work is that to prevent ice sheet collapse the “perturbation” that creates the warming that is responsible for ice sheet collapse, which is mostly ocean warming, must end by at the latest 2050. This means that we must return ocean temperature to its preindustrial stable temperature by 2050. The challenge here is that it is much more difficult to cool the oceans than it is the atmosphere. Figure 3 shows the model runs that define the stable state in blue.
Feldmann and Levermann, Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin, PNAS, November 17, 2015.
http://www.pnas.org/content/112/46/14191.full.pdf
- Abrupt sea level rise of 10 feet per century for centuries on end…
Up to 60 mm per year… Reef backstepping identifies abrupt sea level rise of up to 63 mm per year that persisted for 300 to 500 years. This summary of research looks at three recent deglaciation when both northern and southern ice sheet contributed and a sea level jump during our previous interglacial when the north American Ice Sheet (Laurentide) was absent at 121,000 years before present.
Blanchon, Meltwater Pulses. In: Hopley, D. (Ed), Encyclopedia of Modern Coral Reefs: Structure, form and process. Springer-Verlag Earth Science Series, p. 683-690, 2011.
https://www.academia.edu/421179/Meltwater_Pulses_Encyclopedia_of_Modern_Coral_Reefs
40 mm per year…
Deschamps et al., Ice-sheet collapse and sea-level rise at the Bolling warming 14,600 years ago, Nature, March 29, 2012.
http://www.grandkidzfuture.com/earths-climate/ewExternalFiles/meltwater%20pulse%201A%20Nature%202012.pdf
20 feet… O’Leary – Australia, The authors say 6m (20 feet) of sea level rise at 120,000 year before present in 1,000 years. Their data appear to show a few hundred years.
Oleary et al., Ice sheet collapse following a prolonged period of stable sea level during the last interglacial, Nature Geoscience, July 28, 2013.
http://moraymo.us/wp-content/uploads/2014/04/olearyetal_natgeo_20131.pdf
20 to 29 feet… Sea level in recent interglacials with the Eemian, MIS 5e (~129,000 to 116,000 years ago) experiencing sea level rise of 6 to 9 meters above today and a global temperature a few degrees C above today. During MIS 11 (Mid Pleistocene, ~424,000 to 395,000 years ago) there was 6 to 13 m of sea level rise and the temperature was about the same as today.
Dutton et al., Sea-level rise due to polar ice-sheet mass loss during warm periods, Science, July 10, 2015.
65 feet plus sea level rise mid-Pleistocene…
Hearty, MIS 11 rocks! The “smoking gun” of a catastrophic +20 m eustatic sea-level rise, Pages, April 2007.
http://www.pages-igbp.org/download/docs/newsletter/2007-1/open_highlights/Hearty_2007-1(25-26).pdf
Hearty et al., A +20 m middle Pleistocene sea-level highstand (Bermuda and the Bahamas) due to partial collapse of Antarctic ice, Geology, 1999. (abstract only)
http://geology.gsapubs.org/content/27/4/375.abstract
Hearty, The Kaena highstand on Oahu, Hawaii: Further evidence of Antarctic Ice collapse during the middle, Pacific Science, 2002. https://www.researchgate.net/publication/29737777_The_Ka’ena_Highstand_of_O’ahu_Hawai’i_Further_Evidence_of_Antarctic_Ice_Collapse_during_the_Middle_Pleistocene
- Recent sea level rise rate jump… Sea level rise from 1900 to 1990 was about 1.5 mm per year and from 1990 to 2010 3.2 mm per year. Since 2010 there seems to have been a another jump in the sea level rise rate that puts it above 5 mm per year based on NOAA’s sea level data.
http://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/LSA_SLR_timeseries.php - Dynamical Ice Sheet Collapse Modeling Arrives…The abstract from DeConto and Pollard states: “model coupling ice sheet and climate dynamics—including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs—that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 13 metres by 2500, if emissions continue unabated.”
DeConto and Pollard, Contribution of Antarctica to past and future sea level rise, Nature, March 31, 2016.
Abstract: http://www.nature.com/nature/journal/v531/n7596/full/nature17145.html?WT.feed_name=subjects_earth-and-environmental-sciences
Full: http://www.documentcloud.org/documents/2823837-DeConto-Pollard-2016-Contribution-of-Antarctica.html
- Sea level rise of over 10 feet in 100 years during the previous interglacial warm period 121,000 years ago… During the short warm period before our last 100,000 year-long ice age very similar to what we are experiencing today, marine archeologists tell us a reef called Xcaret was suddenly drowned. This reef was in a stable area of the Yucatan Peninsula not affected by subsidence or geologic uplift processes. Some corals are very picky about the depth of water that they grow in and the Elkhorn coral in particular was devastated by a sea level jump of 12 feet about 121,000 years ago. This time frame matches fairly well with the most recent collapse known of the West Antarctic Ice sheet from research by the British Antarctic Survey in 2010. The jump happened in a time period similar to that of the life of an elkhorn coral, which is 12 to 24 years.
Blanchon, et al., Rapid sea level rise and reef back stepping at the close of the last interglacial highstand, Nature, April 2009. First Paragraph, page 884: “During those jumps, direct measurement of rise rates shows that they exceeded 36 mm per year.” (1.2 feet per decade)
- West Antarctic Ice Sheet Collapse Began Shortly After the Turn of the Century… Vaughan summarized the science around West Antarctic Ice Sheet Collapse beginning in 1981. While the mechanisms for ocean melt were present in publication from the early 1990s, it was not until the early 2000s that work first showed definitive evidence of thinning, grounding line retreat, and ice stream acceleration in one of the most sensitive area of West Antarctica, the Amundsen Sea Embayment. Vaughan concludes that if these symptoms are indeed precursors to collapse, then collapse has begun. From what we know today, he was absolutely correct. Vaughan, West Antarctic Ice Sheet collapse – the fall and rise of a paradigm, Climatic Change, 2008, see the abstract.
http://www.researchgate.net/publication/225166993_West_Antarctic_Ice_Sheet_collapse__the_fall_and_rise_of_a_paradigmd
- Increased Antarctic Sea Ice Increases ocean warming…The underice melt caused by ocean warming creates a feedback where the fresh water melt floats on the saltier ocean water, less salty water freezes faster and the combination of the isolation of saltier water from the surface due to the layer of fresh water and increased presence of sea ice decreases cooling caused by wind mixing during the Antartic Autumn and winter.
Bintanja et al., Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion, Nature Geoscience, March 31, 2013.
Researchgate (free account: https://www.researchgate.net/publication/258807299_Important_role_for_ocean_warming_and_ice-shelf_melt_in_Antarctic_sea-ice_expansion - Amundsen Sea Embayment… The Amundsen Sea Embayment includes several of the largest outlet glaciers in West Antarctica and is likely the Achilles Heel of the WAIS. It is thinning more rapidly and has seen velocity increases higher than anywhere in Antarctica and its retreat is linked to complete Collapse of the WAIS in modeling.
Sutterley et al., Mass loss of the Amundsen Sea Embayment of West Antarctica from four independent techniques, Geophysical Research Letters, December 15, 2014.
http://www.ess.uci.edu/sites/default/files/pictures/grl52351.pdf - Underice melt in excess of 100 meters per year… Amundsen Sea Embayment, Pine Island Glacier at the grounding line.
Dutrieux et al., Pine Island glacier ice shelf melt distributed at kilometre scales, The Cryosphere, September 26, 2013.
http://www.the-cryosphere.net/7/1543/2013/tc-7-1543-2013.pdf - Self Imposed Speed Limit on Ice Cliff Collapse… Personal communication, May 15, 2016, Prof. Rob DeConto, Department of Geosciences, University of Massachusetts-Amherst.