I bagged a long sought after interview late last March, with Jeff Severinghaus (we have a connection I’ll explain tomorrow) of Scripps Oceanographic Institute.
Big Ice guy.
Jeff has some current research that I’ll be examining in coming videos, but as I spoke to Jeff he was just returning from a stay in Antarctica, so I asked him to summarize the best assessments.
Then of course, Covid hit, and my county in Michigan got devastated by a dam failure, and a whole load of the madness that is 2020 got in the way – but I finally came back around to this.
I matched Jeff’s clips with some from Richard Alley and Eric Rignot, well known to readers here. They spoke to me in New Orleans in 2017.
I had also talked to Susheel Adusumilli, also of Scripps, and I featured prominently the new work from Stef Lhermitte, of Delft University of Technology. Then I wrapped it with a summary from Twila Moon of the National Snow and Ice Data Center.
My Yale Climate Connections colleague Karen Kirk also had a pass at this research as well, her @CC_Yale piece:
Karen Kirk in Yale Climate Connections:
Climate researchers have long monitored ice sheet dynamics in the Amundsen Sea, focusing specifically on the Thwaites and Pine Island glaciers. The two sit side by side on Antarctica’s western peninsula covering an area roughly the size of nine U.S. coastal states stretching from Maine to Maryland. The two glaciers alone store ice that could account for about 4 feet (1.2 meters) of global sea level rise. Their “seaboard” location may help bring increased public attention and interest to the West Antarctic Ice Sheet, which if it melted could raise seas by a catastrophic 11 feet (3.4 meters).An international effort led by the British Antarctic Survey recently published two papers (Hogan et al. and Jordan et al.) showing the first detailed maps of the seafloor at the edge of the Thwaites Glacier. The team mapped deep submarine channels that have been funneling warm water to this vulnerable location. High-resolution imagery pinpoints the pathways that allow warm water to undermine the ice shelf. Lead author Kelly Hogan of the British Antarctic Survey says the findings will improve estimates of sea-level rise from Thwaites Glacier. “We can go ahead and make those calculations about how much warm water can get under the ice and melt it,” Hogan said.
The other researchers, led by Stef Lhermitte, found stark visual confirmation of glacier disintegration using decades of time-lapse satellite imagery. Their work sheds light on the accelerating feedback process, wherein the rapid loss of ice is opening the door to ever-increasing melting.
Hogan’s team studied the warm, salty current called the Circumpolar Deep Water, which follows undersea channels directly to the front of the Thwaites Glacier. This process is “thought to be one of the major culprits for melting at Thwaites,” Hogan said in a recent radio interview. To compile this data, the team undertook a two-month journey aboard the Nathaniel B. Palmer, a 300-foot icebreaker specially equipped for scientific research.
The scientists found seafloor channels to be more than 2,600 feet (800 meters) deep, several hundred meters deeper than originally thought. As a result, the amount of warm water that can reach the ice front is also larger than previously believed, with more warm ocean waters able to erode the ice shelf from the bottom up.
Thus, the accelerated feedback process: First, the floating portion of the ice shelf thins, cracks, and breaks apart. Also, the “grounding line” where the ice rests on the sea floor retreats landward. Since the grounding line anchors the ice sheet, its retreat is like kicking the chair out from under a seated person. As the grounding line moves landward, the ice shelf is destabilized. Large slabs of ice can detach, or “calve” into the open sea. Warm ocean water gains access to new areas of ice, fueling more melting.
Another study released earlier in September shows the visible effects of a warming climate on the Thwaites and Pine Island Glaciers, using time-lapse satellite imagery dating back to 1973. The images show the ice weakening, thinning, retreating, and breaking apart, evidence of a decline in the ice shelves that could possibly lead to wholesale collapse.
This series of images shows the ice front at Pine Island Glacier in a more or less stable position from 1973 to 2014, and then a startling retreat in 2015 through the present. Roughly 30% of the ice shelf disappeared over the past six years.
These time-lapse photos Movie S5 from Thwaites Glacier span a 20-year transition from an ice surface that was smooth and solid to one that became fractured and crevassed as it ripped apart.
In this video Movie S3 the ice shelf that had been holding Thwaites Glacier in place has been reduced to “melange,” a fluid mixture of ice fragments. These remnants of the formerly solid ice offer none of the buttressing effect of a solid ice shelf.
The research team documented other effects too: the glaciers and their ice shelves are thinning, and the speed of glacial outflow has increased. Both of these processes contribute directly to rising seas.
Concern over ‘further disintegration’ of glaciers
The observed changes to these glaciers are worrisome enough, but the authors are especially troubled by signs that the decline is speeding up. Lhermitte and his co-authors posit that the types of damage they documented are signs that “these ice shelves are already preconditioned for further disintegration.”
Edit:Greenman — They spoke to me in New Orleans in 1917.
Unless I’m missing something, there is some force of habit kicking in here.
Fee free to delete this comment
Not mentioned in connection to the retreating grounding line and warm water influx is the often retrograde slope the glacier is resting on.
Its in the “Meltwater Pulse 2B” vid embedded above.
too much to jam into one video.
What Rignot told me is that if the seawater coming up against the base of the ice gets cooler, the retreat can slow down as ice flowing in will replace the melted ice more efficiently.
That’s assuming really major progress against warming, and maybe even some drawdown of CO2.
Any models for isostatic rebound related to ice loss for both Greenland and Antarctica? I haven’t seen anything. Specifically, I wonder what might this rebound rate do to affect global sea level rise or if it factors in these present day models at all?
good question, I don’t have anything on that
A I understand it, it’s a very slow process (still underway after the ice age in some places…).
correct. It is a process of thousands, if not tens of thousands of years.
Greenland isostatic rebound recently discussed in
Khan, S.A., Bjørk, A.A., Bamber, J.L. et al. Centennial response of Greenland’s three largest outlet glaciers. Nat Commun 11, 5718 (2020). https://doi.org/10.1038/s41467-020-19580-5
Bottom line – For Greenland, isostatic rebound effect on Greenland outflow glaciers estimated to be insignificant.
For Antarctica, see
Gomez, N., Pollard, D. & Holland, D. Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss. Nat. Commun. 6, 8798 (2015).
and
Larour, E. et al. Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks. Science 364, 969 (2019).
“Solid earth uplift and local sea level lowering
Beside atmosphere and ocean cooling40, a potential mechanism that can have a stabilizing effect on a retreating marine glacier is the solid Earth uplift and local sea level lowering as modelled and observed in Antarctica41,42. Over the 20th century climate has become warmer in the Arctic and as glaciers lose mass the pressure at the bedrock surface decreases resulting in uplift of the solid earth. The earth’s instantaneous elastic response to contemporary changes in ice mass (Supplementary Fig. 1), and glacial isostatic adjustment i.e., the delayed viscoelastic response to past changes in ice loads (Supplementary Fig. 1) show meter-level land uplift over the 20th century. Decreases in local gravity caused absolute sea level lowering shown in Supplementary Fig. 1. In total, the relative sea level lowered by ~280 cm and 350 cm during 1880–2012 near the present-day grounding lines of Jakobshavn Isbræ and Kangerlussuaq Glacier, respectively (Fig. 5a, b). For Helheim Glacier we estimate a much smaller relative sea level lowering of ~40 cm near its grounding line (Fig. 5c). We posit that the change in local sea level has not had a strong effect on ice dynamics, as these glaciers are tidewater glaciers and do not have a significant floating section. Sea level fall therefore does not lead to a grounding line advance and only changes the water pressure at the calving front. The negative feedback observed and modelled in Antarctica 41,42 is therefore not a relevant mechanism in Greenland and we do not expect it to have any significant influence on ice dynamics and ice front retreat.”
https://www.nature.com/articles/s41467-020-19580-5
Thanks, Glen.
It seems to me quite reasonable to think that when glacial ice melts, that contribution will raise sea levels. But I also think isostatic rebound will further that rise as land relieved of this weight displaces even more ocean. I have no data to support this hypothesis but it makes sense to me… even though I’ve never come across any predictive sea level rise model that seems to include this physical phenomena.
This study addresses the effect on grounding lines and mentions lowering sea level but I suspect this lowering is strictly relative to local (and rising) coastal land – ice leaves, land rises at some pace – and not for the absolute rise in ocean levels. Nevertheless, I do think rebound is a factor – to what if much effect I do not know – in predicting absolute sea level rise from large scale melting ice… a factor I do not think is usually considered in these predictive models because I’m having very little luck in finding any that do.
Although I understand and appreciate the difficulty in quantifying this physical phenomena, just the fact that we know land rises when significant ice melts is enough to know it will play some role in raising the global sea level.
Greenland isostatic rebound recently discussed in
Khan, S.A., Bjørk, A.A., Bamber, J.L. et al. Centennial response of Greenland’s three largest outlet glaciers. Nat Commun 11, 5718 (2020). https://doi.org/10.1038/s41467-020-19580-5
Bottom line – For Greenland, isostatic rebound effect on Greenland outflow glaciers estimated to be insignificant.
For Antarctica, see
Gomez, N., Pollard, D. & Holland, D. Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss. Nat. Commun. 6, 8798 (2015).
and
Larour, E. et al. Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks. Science 364, 969 (2019).
———————————————–
Khan et al. 2020 on isostatic rebound in Greenland:
“Solid earth uplift and local sea level lowering
Beside atmosphere and ocean cooling40, a potential mechanism that can have a stabilizing effect on a retreating marine glacier is the solid Earth uplift and local sea level lowering as modelled and observed in Antarctica41,42. Over the 20th century climate has become warmer in the Arctic and as glaciers lose mass the pressure at the bedrock surface decreases resulting in uplift of the solid earth. The earth’s instantaneous elastic response to contemporary changes in ice mass (Supplementary Fig. 1), and glacial isostatic adjustment i.e., the delayed viscoelastic response to past changes in ice loads (Supplementary Fig. 1) show meter-level land uplift over the 20th century. Decreases in local gravity caused absolute sea level lowering shown in Supplementary Fig. 1. In total, the relative sea level lowered by ~280 cm and 350 cm during 1880–2012 near the present-day grounding lines of Jakobshavn Isbræ and Kangerlussuaq Glacier, respectively (Fig. 5a, b). For Helheim Glacier we estimate a much smaller relative sea level lowering of ~40 cm near its grounding line (Fig. 5c). We posit that the change in local sea level has not had a strong effect on ice dynamics, as these glaciers are tidewater glaciers and do not have a significant floating section. Sea level fall therefore does not lead to a grounding line advance and only changes the water pressure at the calving front. The negative feedback observed and modelled in Antarctica 41,42 is therefore not a relevant mechanism in Greenland and we do not expect it to have any significant influence on ice dynamics and ice front retreat.”
https://www.nature.com/articles/s41467-020-19580-5
ooops, tried to edit post and duplicated it instead…Peter – please delete the first version.