Surface Melting an Increasing Factor in East Antarctica?

Or so says Climate Denial Crock of the Week. There's no real text behind the headline, just a link to a WSJ video. This seems to be about Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf, J. T. M. Lenaerts et al., Nature Climate Change (2016) doi:10.1038/nclimate3180, published online 12 December 2016. Here's the abstract:

Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves1, 2 causing grounded glaciers to accelerate3 and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line4, which in the recent past has led to the disintegration of the most northerly ice shelves5, 6. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing7.

The paper itself may be marvellous, I wouldn't know, it is paywalled. I don't understand the bit about the katabatic winds properly: in my world, katabatic winds are cold, which is why they flow off the continent. If they were warm, they wouldn't. I can see that they will entrain air from outside the boundary layer that would be warmer, but if they warm too much again they stop flowing. The bit about winds blowing the snow clear and exposing blue ice is familiar, though. And that the albedo of such ice is lower than the snow is kinda obvious. That East Antarctic (as opposed to West) ice shelves are warm enough to melt from above is something of a surprise for me. ScienceDaily's Mysterious 'crater' on Antarctica indication of vulnerable ice sheet is the same story I think, and includes "The crater isn't new; we found it on satellite images from 1989. The amount of melt water differs immensely from year to year, but it clearly increases during warm years". Ah, but that is them finding it retrospectively: it probably wasn't known in my time.

What seems to be missing is context: how large is the melt, what fraction of snowfall is it, what would it be if translated into mm of SLR?

Apparently co-incidentally Scientists confirm that warm ocean water is melting the biggest glacier in East Antarctica (an improvement on the dreadful fb link I got it from, titled "warm ocean water is slamming into - and melting - the biggest glacier in East Antarctica. Which is really Ocean heat drives rapid basal melt of the Totten Ice Shelf in "Science Advances" by Stephen Rich Rintoul et al., 16 Dec 2016: Vol. 2, no. 12, e1601610, DOI: 10.1126/sciadv.1601610. This essentially confirms what we already knew, because altimetry tells you the surface is sinking, but it is nice to have direct observations. Sub-ice-shelf melting was a thing the glacios loved, well before I left.

More like this

Michael Tobis reports from AGU on presentations by Deconto and Pollard:

"It turns out that this addition ice-sheet cliff collapse] is sufficient to capture the paleo-Milankovic sea level oscillation!

Then these guys do the right thing and do a formal Bayesian tuning of model parameters to paleo-obs, and have a good claim to getting the problem first-order right for the first time. And things look pretty solid.

Which in turn strongly indicates that Hansen’s much-maligned sense of it is in fact correct – large ice sheets can collapse quite quickly. (I went with the crowd in dismissing that idea. Oops.)"

Day 4 at AGU – Productive Self-Doubt and Healthy Retraction

By Kevin O'Neill (not verified) on 18 Dec 2016 #permalink

I think katabatic winds warm because the air becomes compressed as it travels downslope.

By Harry Twinotter (not verified) on 18 Dec 2016 #permalink

Easy to check that about 25 meters of sea level rise are to come, just based on 400 ppm of carbon dioxide and checking the last time the carbon dioxide concentration was as high, mid-Pliocene. Maybe this is coming rather faster than previously estimated.

By David B. Benson (not verified) on 18 Dec 2016 #permalink…
"OSIRIS images of Comet 67P/Churyumov–Gerasimenko showing the details of a 500 m-long crack running through the Hapi region...."

I wonder if the observations of a comet developing a large crack has any use to figuring out how ice caps break up into chunks (cited in my "ice cube catastrophe scenario" op. cit)

By Hank Roberts (not verified) on 18 Dec 2016 #permalink

Hank -

A better analogy might be 'Orogenic collapse' (no tittering at the back, please). Basically, if you pile up too big a mountain range, like the Himalaya, it starts to develop extensional faulting and 'flow outwards' even though the overall tectonic regime is one of strong compression. Something similar may happen with ice sheets when they lose a seaward-facing part and become gravitationally unstable, except quite a lot faster.

By Andrew J Dodds (not verified) on 19 Dec 2016 #permalink

If the katabatic winds were entraining warmth all along their length or more so near the source end then perhaps they would be slowed or stopped if warmed enough.

Could be wrong, but isn't the effect being suggested that thin ice shelves mean the ocean is warming the air particularly near any cracks.

[No, that's not possible. They are far too thick for that; heat flow through the ice shelf / sheet is negligible -W]

While the katabatic winds want to get under warm air over the ocean, this upward motion and/or turbulence caused pushes some of the katabatic wind up so warm air gets pulled down. This will only be happening a short distance inland.

Does then tend to help katabatic winds get stronger rather than weakening them?

To support above, see diagram 1:16 into WSJ video. The curl in the wind is over ocean not along whole length of katabatic wind.

[I think not. That curl - which is largely schematic, so don't over-interpret it - it probably intended to be the entrainment of warmer air into the boundary layer. It is a cause of the melt, not a consequence -W]

"Our model treats glacier ice as a granular material made of interacting boulders of ice that are bonded together. Simulations suggest that different calving regimes are controlled by glacier geometry, which controls the stress state within the glacier. We also find that calving is a two-stage process that requires both ice fracture and transport of detached icebergs away from the calving front. We suggest that, as a result, rapid iceberg discharge is possible in regions where highly crevassed glaciers are grounded deep beneath sea level, indicating portions of Greenland and Antarctica that may be vulnerable to rapid ice loss through catastrophic disintegration."

By Hank Roberts (not verified) on 19 Dec 2016 #permalink

"Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6–9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a 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 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years."

By Phil Hays (not verified) on 19 Dec 2016 #permalink

See NOAA sea level data-No chaneg in level trend back to mid 1800s; no ice cap melt=No warming.…

[That individual plot shows no evidence of acceleration, agreed (but it is a crude "analysis", if that. is more instructive). But how you get from there to "no ice cap melt=No warming" baffles me. Could you lay out your logic more clearly? -W]

By FrankChanged (not verified) on 19 Dec 2016 #permalink

Blue ice comment seems rather hopeful, I have never seen a picture of flat ice surface in Antarctica without layers of that white fluffy stuff on it.

[That would have been a reasonable comment, if you hadn't already been pointed at the concept of "blue ice". Google should have found it for you, with only a moderate degree of effort on your part; e.g. -W]

Second the study "Scientists confirm that warm ocean water is melting the biggest glacier in East Antarctica " is a bit lame is it not.
It shows that the water next to the ice is hot enough to melt it at depth in Summer.
The fact that all water close to ice is warmer than ice seems to have escaped them,

[ -W]

more so that the ice is melting in Summer when the sun naturally puts more heat into the ocean.
Cold ocean water melts ice, now that would be a headline!
Then there is the whole ocean/ glacier thing. If it is in the ocean it is technically not a glacier. What they are talking about is an ice shelf.
Worse they are saying it restrains the Glacier and when it breaks away or melts the Glacier will run [stroll?]more freely to the ocean. In actual fact Glacier flow [acting like a liquid] will actually soon reduce as there will be less volume to flow.

Frank, I have lived near the waterfront in Boston since 1984, and visited before that, and I have incontrovertible photographic evidence of sea level rise here. It has been a slow process, but in the last few years it has shown gathering strength.

Your local authorities provide this:

Once the process gets under way, it is too late.

By Susan Anderson (not verified) on 20 Dec 2016 #permalink

Might Frank be something other than American? I've meet some very clueless Canadians, British and Kiwis.

No personal meeting with clueless Australians yet, but the sample size isn't large. And news reports and blogs of said are easy to find.

By Phil Hays (not verified) on 21 Dec 2016 #permalink