Monday, May 12, 2014

Something Scary Comes This Way

Two papers have appeared today which, in the words of Richard Alley, are the equivalent of the guys over in the corner screaming bloody murder.  Both describe the coming, and in their view, inevitable collapse of the West Antarctic ice shelf at some point in the next 200-900 years.  While the exact time of collapse is not predictable, the inevitability is, and 200 years is not so long in the future.

Rignot, Mouginot, Morlighem, Seroussi and Scheuch map the observed retreat of these grounding glaciers, and over the past twenty years, and yes, once they let go, there is nothing holding the ice shelf back from lurching into the Southern Ocean.  They conclude
Using two decades of ERS-1/2 data, we document a continuous and rapid retreat of the grounding lines of Pine Island, Thwaites, Haynes, Smith and Kohler glaciers, which drain a large sector of West Antarctica on a retrograde, submarine bed, a configuration deemed unstable by ice sheet numerical models (e.g. Favier et al., 2014, Katz and Worster, 2010; Parizek et al., 2012) unless normal and tangential ice shelf buttressing could increase significantly (Gudmundson, 2013), which is unlikely. The retreat is proceeding along fast-flowing, accelerating sectors that are thinning, become bound to reach floatation and un-ground from the bed. We find no major bed obstacle upstream of the 2011 grounding lines that would prevent further retreat of the grounding lines farther south. We conclude that this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise in decades to come.
The process is an avalanche, with the ungrounding of the blocking Twaites and Pine Island Glaciers leading to rapid collapse.  From the paper by Joughin, Smith and Medley appearing in Science,
When simulated losses exceed 1 mm/yr sle, much greater losses generally follow within a few years. Using our basin-­scale model, however, such rapid collapse is difficult to model, especially since interaction with other basins becomes increasingly important. Thus, we take 1 mm/yr sle to be a threshold that, once crossed, marks the onset of rapid (decades) collapse as the grounding line reaches the deepest regions of the marine basin.
Now other bunnies will say this better, and already have, for example, Suzanne Goldenberg and those to be named later, what Eli is looking at is how the Mysterious Mr. Revkin appears, to tweet in glee and error at Ms. Goldenberg
The link goes to a post at his Dot Earth blog at the NY Times, where our hero manages to miss the entire point about the rapid (decades) collapse once the melt exceeds the threshold.  Our Mr. Revkin starts with a quote from the abstract
Except possibly for the lowest-melt scenario, the simulations indicate that early-stage collapse has begun. Less certain is the time scale, with the onset of rapid (>1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.
To translate a bit, that means sometime between 200 and 900 years from now the rate of ice loss from this glacier could reach a volume sufficient to raise sea levels about 4 inches (100 millimeters) a century. At that point, according to the paper, ice loss could pick up steam, with big losses over a period of decades.* But in a phone conversation, Joughin said the modeling was not reliable enough to say how much, how soon.
 The *, of course, is the Pielke *
Update, 8:03 p.m. | * At the asterisk above, I added a phrase indicating that the modeling showed abrupt and large ice losses at the discussed stage some centuries from now.
And, of course, some centuries could be one or two centuries if we are not lucky.

Well, who picks this up but our friend Willard Tony

The Guardian’s Suzanne Goldenberg jumps the shark again – gets called out by NYT

 Except, of course, if the bunnies read the footnotes.  Eli leaves Tony to the Hot Whopper.


Russell Seitz said...

Much as I groan at the Grauniad, I'm bracing for Tony to declare sea levels must inevitably fall as India continues to stuff itself under the Asian plate, making way for lots more Indian Ocean.

Never mind the Greenland Graben rebound once the ice departs- all that subsealevel ice won't begin rising until several elections after the next empire from now .

Anonymous said...

Rignot states that it is a "conservative estimate" that it will take several centuries for all the ice to fully melt. Don't understand the meaning of "conservative" in this context. Wondering what the most likely and the worst-case scenarios might be?

Bill W

Anonymous said...

Wait - is this something actually testable?

Russell Seitz said...

Get out your ice cubes and stopwatch , anon, summer approaches, again.

Bernard J. said...

Revkin needs to curb his pendantry.

The projections of Rignot et al are catatrophic in an ecological context, not only with respect to the WA ice loss but to all the other attendant ice loss around the world, and to the temperature increase that causes it...

It seems that some people think that Twitter is meant for showing the world that one is a twit.

And for the Aussies (and other interested parties) here, the issue was discussed on The World Today:

[Recaptcha anticipated Revkin's increasingly bemusing commentary - "reimuld themselves"...]

Anonymous said...

anonymous#1, yes and you're in the test.

Tenney Naumer said...

Joughin et al. initialized their simulation with the observed velocity that was near to that of 1995. Later, they state:

"The retreat that does occur is largely driven by the non-steady state fixed velocity imposed at the start of the simulation."


I'm thinking the 200-900 years scenario is somewhat "conservative."

Susan Anderson said...

Correct me if I'm wrong. Glad to have been forced at long last to closely read the numbers.

So, with plugs at the mouth of outlets (Antarctica) and glaciers in the form of hills in the ocean basin (32:54: flying buttresses, friction, rocky sides, islands) that in the end would release dammed material at a more rapid rate. This would mean a kind of quantum melting. I got all this from Alley in various presentations such as that at the AGU:
(ice review starts just after minute 29)

And why you all still bother with Revkin (as do and did I here) beats me.

Jim Eager said...

Susan, beyond the initial increase in outward flow, my understanding is once the fixed ice retreats beyond the grounding line, warmer sea water will be able flow into the retrograde basin behind the grounding line, melting the bulk of the remaining ice in place from below.

Steve Bloom said...

In place? I haven't read the paper, but my impression from past research was otherwise, i.e. that undermining would cause serial collapse of the ice front, allowing the resulting bergs to drift northward and mostly get melted there. This is actually what happens now, but much more slowly.

Jim Eager said...

OK, make that break up in place, as opposed to flowing past the old grounding line and breaking up there as now happens.

E. Swanson said...

In the linked post on Watts' site, ol' Anthony the climate data guy posted a graph of southern hemisphere temperature history from RSS. The graph clearly states "70S to 0", yet Anthony calls it "from 70S to the pole". Sorry, Anthony, RSS does not provide any data poleward of 70S, because of the high altitude surface influence on the MSU/AMSU instruments. Anthony really needs to do his homework. Maybe then he could convince Christy and Spencer to stop presenting Antarctic data as well...

EliRabett said...

Eric, Eli mentioned this over at WUWT, let us see how they respond.

EliRabett said...

Begad, he took it down. Almost blushed.

Magnus Westerstrand said...

Hi andy,

Bernard J. said...



Dano said...

Everyone should take a look at Magnus' link. Might be my favorite of all time.



Lionel A said...

Jim Eager:

'...warmer sea water will be able flow into the retrograde basin behind the grounding line, melting the bulk of the remaining ice in place from below.'

I have found that GeoMapApp

can be put to interesting use with the ability to create transect of the Earth's surface being apposite.

Does need Java.

It is also interesting to create transects of Greenland which demonstrate the nature of that topography.

Others may know of other software to do similar.

Aaron said...

The bottom line is that the ice is now floating and can do what it wants.

A very good example of ice doing what it wants is at minute 64 of Chasing Ice by J. Balog.

Ice that warms under stress is inherently discontinuous. Floating ice is stressed by tide and swell. These stresses work the ice (adding heat) warming and weakening the ice allowing it to fracture and calve in ways not contemplated in models.

How fast can the process go? It goes fast enough that most of the time we do not see it, so we do not model it.

Lionel A said...

'Chasing Ice' is a must see, I am considering purchasing a number of extra copies and spreading them around friends and family.

Captcha is sentient being part



Jim Eager said...

Lionel, Richard Alley went through this at last year's AGU at about 37:00-38:00 in this video:

There's a more recent clip of him describing how this makes the entire West Antarctic ice sheet vulnerable all the way to the Transantarctic spine, but I can't find the link at the moment.

Lionel A said...

Thanks Jim, Alley as ever the brilliant communicator well remembered for his rapid fire reply to Rohrabacher nonsense:

Alley would not be republican first choice for any future such panels.