By Rud Istvan,
WUWT reader KS of North Dakota emailed a request to ctm based on reading ‘alarming’ Wired journalism concerning $50 million being spent to further study the ‘dangerous’ Thwaites glacier in Antarctica. KS asked if WUWT could perhaps produce a factual overview. ctm asked me to provide it, since I had written an extensive essay ‘Tipping Points’ in ebook Blowing Smoke on this very sea level rise (SLR) subject (and more). What follows is a lightly rewritten and slightly expanded/updated excerpt for KS and the rest of WUWT.
There are only three ice sheets in the world with the potential to accelerate SLR to alarming levels: Greenland, the East Antarctic Ice Sheet (EAIS) and the West Antarctic Ice Sheet (WAIS).
In ‘theory’ Greenland could melt, since there is observed summer melting. It cannot calve (slide into) into the sea (although there are fringe glaciers like Jacobshaven that do, the Titanic sinking being evidence) because Greenland is bowl shaped. At the observed average annual ice mass loss of the past ~2.5 decades (from 1990) Greenland would theoretically take 27000 years to melt. At the ice mass loss rate since 2000, it would only take 14000 years and would increase SLR by a distinctly unalarming ~0.5mm/yr. In reality, given Greenland’s latitude and central ice sheet elevation, melting is impossible—as ice cores reaching back to the Eemian prove. Calculations and references behind this brief summary are provided in ‘Tipping Points’.
With Greenland geophysically debunked, SLR attention turned to Antarctica. [i] Whether Antarctica is net gaining or losing ice is a matter of dispute between NASA (gaining) [ii] and NOAA (losing). [iii] It is a big complicated place. A recent NOAA ice loss estimate is: [iv]
EAIS maybe gaining, WAIS losing, the Peninsula about even. Most of EAIS is anchored by mountains, so cannot ever ‘slide off’. Nor can it ever melt so long as Antarctica sits over the South Pole.
Any SLR alarm has to be found in WAIS, where the general slope is from the Transarctic Mountain divide down to the sea. Some (maybe 2/3) in theory could ‘slide off’, because WAIS cannot melt either. The rest is anchored by the coastward Executive Committee and Ellsworth mountain ranges.
So potential WAIS instability has been the subject of much scrutiny. The main concerns were the grounded portions of the Ronne (which is not really part of WAIS but is still mostly in the Western half of Antarctica) and Ross ice shelves. (Floating shelf ice cannot raise sea level.) These have the largest volumes of grounded ice creeping out onto the seabed, although on an annual basis fresh snow replenishes most of the lost shelf ice inland at higher WAIS elevations. It is the net ice mass balance along these WAIS grounding lines that might give rise to SLR alarms.[v]
Ronne (#1 in the following figure) is net gaining ice mass according to NASA.[vi] A 2012 ice core from the Fletcher Promontory showed Ronne remained stable during the warmer Eemian. [vii] It isn’t a SLR concern. Ross (#19) might or might not be losing ice, but it ‘holds back’ almost half of WAIS. Ross also has more ice grounded on the seabed, which if ungrounded (melted from below), would raise sea levels. For several years Ross became the Antarctic instability ‘alarm’, which is why the ANDRILL program was instigated.
The ANDRILL program was designed to look at the underlying Ross seabed (both where the ice is grounded below sea level, and where it is floating shelf) to understand its behavior. Andrill cores and creep rates suggest it has not collapsed before (well, for at least 3 million years and all previous Pleistocene interglacials), so very likely will not now from global warming. Holocene retreat of the Ross grounding line stopped 4 millennia ago. [viii] Ross bedrock islands ‘anchor’ its grounded ice and retard seaward creep. [ix] The Ross shelf’s seaward creep has decelerated in recent decades. [x], [xi] The ANDRILL program ultimately proved Ross was not alarming either.
Abetted by additional NASA PR and author interviews (Rignot of NASA JPL, “Already gone into irreversible retreat, past the point of no return”, 2014 MSM alarmist headlines were, well, alarming. Reuters reported worldwide: “West Antarctic Glaciers in irreversible thaw: rising seas” [xiv] CNN said: “Ice melt in part of Antarctica ‘appears unstoppable’, NASA says” [xv] MSM TV was worse. [xvi] The KS spotted Wired ‘journalism’ is simply a 2018 echo of this alarmism.
Except the media did not read these papers carefully or in context (if at all). The first paper found Pine Island Glacier (PIG, #22) plus Thwaites (#21) plus lesser Amundsen Sea glaciers have accelerating creep and are now discharging ice into the sea at ±330Gt/yr. That is (330/85) 3.9x higher than any previous estimate, for example NASA’s own from 2011 and 2012. This newest estimate is presently an outlier –but not necessarily wrong– with the likely explanation, volcanism, explained below. The second paper used computer models of Thwaites (#21) bottom melting to conclude it might become unstable in 200 to 900 years. If so, models suggested maybe 1mm/yr of additional SLR thereafter. Not ‘in coming decades’, maybe in coming centuries.
There is a deeper problem with NASA’s version of Amundsen Embayment SLR alarm. The NASA NEWS discussing these papers says the Embayment catchment basin contains enough ice to raise global sea level by 4 feet (1.2 meters). That is true; the basin has a total area of about 360,000 km2 and the ice averages 3km thick. [xvii] But for 1.2 meters of SLR, the entire catchment basin would have no ice at all. That is extremely unlikely, since the interior portions are not flowing seaward according to NASA’s own papers, and are still gaining ice. [xviii], [xix] As the preceding Amundsen Embayment catchment and following NASA illustrations show, PIG and Thwaites glaciers comprise only about 15% of the catchment basin area and less of its ice volume (ice is thicker to the interior).
The media hoopla also ignores another paper on an ice core (F10) (drilled on the divide to Farrigno Glacier, just northwest of PIG) providing a detailed isotope derived temperature record from 1702 to 2009. [xx] F10 shows greater periods of Amundsen Embayment warming and cooling in both the 18th and 19th centuries than in the 20th. It found:
“…the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past ~300 years.”
NASA’s newest accelerated ice loss estimate may not be erroneous. A 2017 paper provided the first physical proof that the Amundsen Embayment, and in particular PIG, sits over an area of active volcanism.[xxi] Volcanic ash was found in its ice cores.
SLR alarm remains popular in media reporting, easily suggested by images of calving WAIS glaciers and summer meltwater rushing down Greenland moulins. But it is all alarmist fantasy rather than remotely possible centennial or even millennial factual possibilities.
[i] Colville et. al., …Isotope Evidence…, Science 33: 620-623 (2011)
[ii] Zwally et. al., Mass Gains of the Antarctic Ice Sheet Exceed Losses, SCAR ISMASS 7/14/2012
[iii] Shepard et.al., A reconciled estimate of ice-sheet mass loss, Science 318:1183-1189 (2012)
[v] Image from the Rignot Research Group, JPL and NSIDC data
[vi] See WUWT 8/20/2013, ridiculous National Geographic Statue of Liberty image
[viii] Doake (British Antarctic Survey), Ice Shelf Stability, Chapter 10 Encyclopedia of Oceans (2001)
[x] Scheuchl et. al., Ice Velocity Change in the Ross and Ronne sectors…, Cryosphere 6: 1019-1030 (2012)
[xi] Hulbe et. al., Recent Changes in the flow of the Ross Ice Shelf, Earth & Planetary Science Letters 376: 54-62 (2013)
[xii] Mouginot et. al., Sustained increase in ice discharging from the Amundsen Sea Embayment, GRL: 2013GL059069 (2014)
[xiii] Joughin et. al., Marine Ice Sheet Collapse potentially underway for the Thwaites Basin, Science 344: 735-738 (2014)
[xiv] Doyle, Reuters, 5/12/2014
[xv] Hanna, CNN, 5/13/2014
[xvi] Brian Williams, NBC 5/12: 13 feet SLR in 100 years. Scott Pelley, CBS: 4 feet by 2114. Diane Sawyer, ABC: 3 feet by 2100 and Florida hard hit.
[xvii] Rignot et. al., Acceleration of Pine Island and Thwaites…, Annals of Glaciology 34: 189-194 (2002).
[xviii] Pritchart et. al., Antarctic Ice Sheet Loss…, Nature 484: 502-505 (2012)
[xix] Medley et. al., Constraining the ice mass balance…with airborne observations of snow accumulation, Cryosphere Discuss. 8: 953-998 (2014)
[xx] Thomas et. al., A 308 year record of climate variability in West Antarctica, Geophys. Res. Lett. 40: 5492-5496 (2013) available at nora.nerc.ac.uk/503527
[xxi] Iverson et. al., The first physical evidence of subglacial volcanism under WAIS, Science Reports 7, 11457 (2017)
via Watts Up With That?
January 8, 2019 at 12:07PM