Don’t believe a word of it, guv

1.5 m sea level rise this century, that is. Nature sez the “estimate released today says that it could be as as much as 1.5 metres (4.9 feet) by the end of this century”. Their source seems to be Reuters, and we’ll pause briefly to condemn the oh-so-typical inflation of the worst case from the range into the only number mentioned in the headline. Sigh.

So… Melting glaciers, disappearing ice sheets and warming water could lift sea levels by as much as 1.5 metres (4.9 feet) by the end of this century,… Presented at a European Geosciences Union conference, the research forecasts a rise in sea levels three times higher than that predicted by the Intergovernmental Panel on Climate Change (IPCC) last year… Svetlana Jevrejeva of the Proudman Oceanographic Laboratory in Britain said the estimate was based on a new model allowing accurate reconstruction of sea levels over the past 2,000 years… But the pace at which sea levels are rising is accelerating, and they will be 0.8-1.5 metres higher by next century… say Reuters. But who told them so?

I presume the relevant press conference must be Will Planet Earth become Planet Ocean? (gurk). Which says Global sea level is expected to rise in this century between 18 and 79 cm according to the IPCC 4th Assessment (allowing for uncertainty in the dynamic instability of ice sheets). It seems that this dramatic trend is set to continue beyond the 21st century, making the field of research concerned with measuring sea level change more important than ever.

So its rather unclear where 0.8-1.5m comes from or how you can get that from monitoring past changes. Extrapolating past change into the future won’t get you more than 0.3m for the 21st century. There is a vaguely promising link on JevreSvet‘s homepage, but… its broken. Sack that webmaster.

Oh, and when I say I don’t believe in 1.5m this century… I don’t rule it out as impossible; but I can’t see how you can get it from this stuff.

[Update: it made it onto R4 at 10; and the beeb has it too. Apparently “The rapid rise in the coming years is associated with the rapid melting of ice sheets.” I think its entirely likely that *if* SLR is much larger than IPCC projections then the excess will come from ice sheets. But how you get that from past data is murky.]

23 thoughts on “Don’t believe a word of it, guv”

  1. The POL website was reorganised and it looks like you need to visit Theme1 under research for the programme pages. No research details though.

    However, is this poster at EGU describing the research in question, do you think?

    Click to access EGU2008-A-02547-1.pdf

    [Quite likely. Still not clear how you get the future out, though it would be a possible extrapolation. Not totally convinced by the poster though – unsure that we know global ocean heat that well; I’m sure I’ve sen stuff (JA?) worrying about implausible oscillations -W]


  2. Confusingly, those folks have several closely-related submissions, but this one (no abstract posted yet) seems to be the relevant one:

    Moore, J.C.; Grinsted, A.; Jevrejeva, S.
    Reconstructing sea level from paleo and projected temperatures 100 to 2100AD

    Looking over the entire listing of sea level submissions, especially the ones from Willis, it appears as if there is some movement toward a much ramped-up melt contribution (which recall Willis et al were pushing for in their erroneous OHC paper), although a French team (inc. Cazenave) could be in disagreement.

    [All this for a talk with no abstract? Dodgy -W]


  3. Possibly it was withheld because of the expected press attention (which obviously they were planning for). OTOH they could have done the abstract as a pure teaser, which many of them are anyway. OTOOH then it wouldn’t have added much to the title.


  4. “All this for a talk with no abstract?”

    It seems from the description that the main point of the talk was the 75 years of PSMSL. There seems more discussed than was just picked up by Reuters & BBC. Is anyone doing a diary of EGU like RC did of AGU, anyone know?

    Anyway, I did post a comment with links to the home pages of the other researchers, but it doesn’t seem to have appeared? I’d expect something on those eventually (beyond the basic write-up on John Moore’s popular science description page).

    [Comments with links seem to get jheld for moderation. John Moore needs to update his web page -W]


  5. Konrad Steffen expects a meter by 2100. S. Jeffress Williams thinks 1 meter is “not unreasonable.”

    [The second one comes up blank, though it does include “Oceans are expected to rise by about 39 inches over the next century”. Steffen… well yes. He says that. But based on what? His personal gut feeling?

    The point, I think, is that there are no shortage of people pushing (or being pushed by journos to give) their own ideas of how much SLR there might be. What is needed is some solid scientific basis for these claims. Or to just admit that we’re all guessing -W]

    I linked this paper in a previous thread showing 1.6 meters per century over several centuries, when temps were roughly equivalent to what we will see by the end of the century. Any comments?

    Click to access Rohlingnature2008.pdf

    [Yeeesss… well, fair enough, it does claim > 1m/C SLR in the past. Figs 2c and 2d aren’t perfectly compatible, though, and if you look at 2d at 124-5 kyr there are clear problems with the measurements showing presumably non-physical oscilating sea levels. They insinuate, but are careful not to commit to, the idea that this comes from Greenland. They say their results should niform debate, and I agree, but it doesn’t settle it: not even for then, but certainly not for the future -W]


  6. There’s also Stefan Rahmstorf’s Science paper from 2007 projecting 0.5 to 1.4m

    Click to access rahmstorf_science_2007.pdf

    “Although a full physical understanding of sea-level rise is lacking, the uncertainty in future sea-level rise is probably larger than previously estimated. A rise of over 1 m by 2100 for strong warming scenarios cannot be ruled out, because all that such a rise would require is that the linear relation of the rate of sea-level rise and temperature, which was found to be valid in the 20th century, remains valid in the 21st century. On the other hand, very low sea-level rise values as reported in the IPCC TAR now appear rather implausible in the light of the observational data.”

    The Jevrejeva findings have been submitted to PNAS, so maybe there’s a preprint somewhere?


  7. William! I have paid $10,000,000 to you and your friends at just for your agreement with my calculation that the sea level will jump by 7-24 meters. What the heck is this fucking post? Could you please erase it as soon as possible? Otherwise you will have to be removed from the face of Earth just like the deniers. Lovely Yours Al Gore


  8. What’s the pressure exerted by a column of water a mile high?

    [About the same as a column of ice? -W]

    There’s your mechanism by which summer meltwater ponds break up the ancient icecap, I think.f A small crevasse full of air doesn’t do much. Fill it with water and it’s enormous leverage.

    If there are any other cracks parallel to the fluid filled one, the water can wedge the wet crack wider and deeper by pushing the ice out into the air-filled cracks around it.

    “My co-workers and I had proposed models [in which] meltwater gets to the bed when a lake fills a crevasse, thus driving the crack down,” says glaciologist Richard Alley of Pennsylvania State University who was not involved in the study. Now glaciologist “[Sarah] Das [and her colleagues] have observed it–more than Niagara plunging into Greenland!”

    In fact, Niagara Falls’s flow per second can be as fast as 202,000 cubic feet (5,720 cubic meters) of water; the glacial lake drained at pace of 307,237 cubic feet (8,700 cubic meters) per second.


  9. Yes, about the same as a column of ice — but we know the ice is moving, we know it has fractures.
    But is there a past record of large meltwater lakes? And of such disappearing so fast?

    I don’t have the volume and time numbers to check that rate of flow calculation (and wonder if it’s credible)

    But it makes sense to me that with a lot of cracks, once water from a surface lake gets into one of them, it will be able to spread that crack at the expense of the others in the surrounding ice. And since it can flow in, it would wedge one gap open.

    And the water _went_ somewhere fast. Have we any sonograms/radar measures of voids under the ice available?

    No? I realize I’m only using logic here.
    But it doesn’t make sense to me that a mile of water will not have a different effect on the ice than the ice in the absence of that water.


  10. But Hank, there’s a reasonable concern that under warmer conditions (with a more intensive as well as longer melt season) things may start to behave differently. Of course people are looking at that, but so far I’ve heard no discussion. My confidence level in assurances that the GIS can’t collapse quickly is not very high given how recently the glaciologists thought it couldn’t happen more quickly than a thousand years or so. We read very frequently about e.g. small and large ways in which the GCMs didn’t account for this or that measured effect, so I’m concerned that there’s at least one more major shoe to drop regarding ice sheet melting behavior.


  11. Also, see here for a cutting-edge discussion of ice sheet modeling, noting the first comment in particular. I think it’s clear we are very far from what’s needed, although obviously the amount of work being put into this has scaled up greatly.


  12. “Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid (<2 hours) drainage of a large supraglacial lake down 980 m through to the bed of the Greenland Ice Sheet initiated by water-driven fracture propagation evolving into moulin flow. Drainage coincided with increased seismicity, transient acceleration, ice sheet uplift and horizontal displacement. Subsidence and deceleration occurred over the following 24 hours. The short-lived dynamic response suggests an efficient drainage system dispersed the meltwater subglacially. The integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup."



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