Meltwater Pulse 1A

NASA’s press office is on the ball. Pn May 12, according to NPR, they

held a press conference to discuss the stability of the West Antarctic Ice Sheet and its potential contribution to future sea level rise. The researchers announced that the ice sheet’s collapse is both underway and unstoppable.

Various media have covered this.

I suppose it is good that this phenomenon is in the public eye, but insofar as I know the only real progress is that that the pulse is at
least in part of Antarctic origin; by elimination it could come from nowhere but an ice sheet; the question was which on or which ones; ice
rafted debris has been found confirming an Antarctic source. But the large amplitude of MeltWater Pulse 1A itself is not really “news” in
the sense of being new.

To my knowledge the scale of this event is first discussed in Till Hanebuth, Karl Stattegger, Pieter M. Grootes; Science V 288 pp 1033 ff
(May 2000)

The necessity for media to have a “news hook” before mentioning some publicly relevant information is unfortunate, but better late than
never I guess. I blogged about the aspect of it that gets peoples attention, in 2007 but I had no news hook.

Anyway, better late than never.


  1. One question though. If I read that correctly, Meltwater Pulse 1a was when the sea level was much lower, so the ice that contributed to that, has already melted and was likely grounded on different area of bedrock. So though it shows that in some set-ups such a melt is possible, it doesn't necessarily say (on its own) that we currently have any such set-up now?

  2. That is correct. The existence of the pulse is only enough to say such a thing is possible. But recent evidence increasingly indicates that it is starting.

  3. The setup we have now is the ice margin retreating to behind the sill. When that happened in Ice Bay, Alaska, the retreat of the glacier to above sea level was quite rapid. By inference, the same will happen to a substantial portion of the West Antarctic Ice Sheet.

  4. Thank you. That's what I thought it might be, and it's nice to know I at lest got the basics.

    (Thanks also to David).

  5. The post seems confused. The May 12th press conference discussed two papers that IIRC didn't even mention meltwater pulse 1A, or if so only in passing, rather they were about recent obs and future prospects. This paper seems to be the one you're talking about.

    FWIW, and since as Adam points out one thing we can be quite sure of is that we can't get a 1A repeat as such since that ice is already gone, the Antarctic paleo melt paper that scared the pants off me was Naish et al. (ANDRILL results) finding high-volume rapid cycling of the WAIS and a considerable chunk of the EAIS prior to the mid-Pleistocene transition. There've been lots of follow-on papers, but this one (press release) seems most notable. Ice moves fast when it's pushed hard.

    This Observer column by Eric Rignot re the implication of the papers discussed on May 12th is very much worth a read.

  6. Yes, but it is a larger system and so the time constant is longer.

    My point here is that while this is being played in the press as a horrifying breakthrough, it is just incremental progress. If you were paying attention you pretty much already knew this.

    I think it is good that it gets some press. However I am very unhappy that it requires sensationalist spin to get that to happen.

  7. I think Rignot is a over the line in that article with "At the current rate, a large fraction of the basin will be gone in 200 years, but recent modelling studies indicate that the retreat rate will increase in the future."

    What does that mean? The current rate of what? A large fraction of what? 200 years until what?

    This can easily be interpreted as saying that huge sea level rises are in store over the next few decades. Indeed, Peter Sinclair has run with that interpretation, unwisely I think.

    As far as I know there is no evidence for that. The ambiguity could be sloppy (Rignot is obviously a native French speaker) but it smacks of deliberately leaning toward implicit overstatement to me.

    Why be tendentious in this way? It's not as if we don't have enough problems already.

  8. Pingback: Another Week in the Ecological Crisis, June 8, 2014 – A Few Things Ill Considered

  9. "What does that mean? The current rate of what? A large fraction of what? 200 years until what?"

    To know those things would involve reading the paper and the relevant literature.

    In brief, the basin is the Amundsen Sea Embayment, the rate refers to the measured ice loss of the ASE glaciers, the large fraction refers to most of the ASE ice (1.2 meters SLR-equivalent), and the 200 years refers to how long it will take to empty at the current loss rate.

    So we pass the first major tipping point, and you respond by not doing your homework, handwaving to unnamed glaciologists you talked to a few years ago (lots of ice down the fjord since then, literally and figuratively), and grousing about the communications skills of one of the PIs. Meh,

    Anyway, let's be clear about the importance of this: The ice sheets have been moving much faster, the loss rate is accelerating, there's a lot of ice vulnerable to marine warming, the rate of marine warming is also increasing (thanks, ultimately to us via expansion of the tropics) and there's no means of placing an upper end on the process. Prior work, most prominently Pfeffer et al., purporting to find otherwise is a dead letter.

    Oh look, more swell ice sheet news from just yesterday:

    "Melting and refreezing of deep Greenland ice speeds flow to sea: Findings may shift understanding of ice sheet behavior"

    Interesting times for ice sheet modelers.

  10. I intend to respond in detail after I've done my homework. I strongly suspect Rignot has gone too far but I do have room for doubt.

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