Posts Tagged ‘Seal Level Rise’

Runaway Antarctica

April 1, 2016

I have written for years that a runaway Antarctica was certain, with half the icy continent melting rather spectacularly on an horizon of two centuries at most, and probably much less than that. This rested on the fact that half of Antarctica rests on nothing but bedrock at the bottom of the sea. At the bottom of what should naturally be the sea, in the present circumstances of significant greenhouse gas concentrations.

Visualize this: until sometimes in the Nineteenth Century, GreenHouse Gas (GHG) concentration was 280 ppm (280 parts per million), including the man-made sort. Now we are close to 500 ppm, using a variety of exotic gases we produce industrially, among them, CO2. In CO2 alone we are at:  Week beginning on March 20, 2016: 405.62 ppm. Weekly value from 1 year ago: 401.43 ppm. Weekly value from 10 years ago: 382.76 ppm. So the CO2 alone is augmenting at a bit more than 1% a year. Thus we will be at an equivalent of 550 ppm in ten years (including the full panoply of all the other man-made greenhouse gases, not just CO2). There is evidence that, with just 400 ppm, disaster is guaranteed.

Now visualize this:

How Antarctica would appear if its ice melted: it’s half under the sea.

How Antarctica would appear if its ice melted: it’s half under the sea.

Why so watery? Because the enormous glaciers, up to nearly 5,000 meter thick, press down on the continent with their enormous weight. Since the end of the last glaciation, 10,000 years ago, Scandinavia has been rising, and is still rising (I long used a picture with a similar information about Antarctica’s bedrock.)

A paper published on line in Nature on March 30, 2016, that is, two days ago, “Contribution of Antarctica to past and future sea-level rise” opines that:

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.

Notice that the scenario evoked in the last sentence is different from my  very old scenario, which is similar to the one advanced in November 2015 by the famous Hansen and Al. (I raised the alarm before Hansen, at least seven years ago). In my scenario, and Hansen’s the ice sheets melt from below, due to warm sea water intrusion.

The West Antarctic Ice Sheet is larger than Mexico.

Here is a taste of the paper (I have a Nature subscription):

“Reconstructions of the global mean sea level (GMSL) during past warm climate intervals including the Pliocene (about three million years ago)1 and late Pleistocene interglacials2, 3, 4, 5 imply that the Antarctic ice sheet has considerable sensitivity. Pliocene atmospheric CO2 concentrations were comparable to today’s (~400 parts per million by volume, p.p.m.v.)6, but some sea-level reconstructions are 10–30 m higher1, 7. In addition to the loss of the Greenland Ice Sheet and the West Antarctic Ice Sheet (WAIS)2, these high sea levels require the partial retreat of the East Antarctic Ice Sheet (EAIS), which is further supported by sedimentary evidence from the Antarctic margin8. During the more recent Last Interglacial (LIG, 130,000 to 115,000 years ago), GMSL was 6–9.3 m higher than it is today2, 3, 4, at a time when atmospheric CO2 concentrations were below 280 p.p.m.v. (ref. 9) and global mean temperatures were only about 0–2 °C warmer10. This requires a substantial sea-level contribution from Antarctica of 3.6–7.4 m in addition to an estimated 1.5–2 m from Greenland11, 12 and around 0.4 m from ocean steric effects10.”

So notice: when CO2 ppm per volume was at 280 130,000 to 115,000 years ago, sea level was up to ten meter higher than now. And now we are at 500 ppmv…

And notice again: When CO2 ppmv was at 400, sea level was up to 30 meters (100 feet) higher than today. And now we are at 500 ppm, and, in a blink, in ten years, at 550 ppm.

Here is another example from the paper. I said all of this before, but to have scientists paid to do research in this area write it black on white in the world’s most prestigious scientific magazine, will no doubt endow me with greater, and much desired, gravitas. So let me indulge, not so much for my greater glory, but because it should help taking what I have long said more seriously.

“Much of the WAIS sits on bedrock hundreds to thousands of metres below sea level (Fig. 1a)13. Today, extensive floating ice shelves in the Ross and Weddell Seas, and smaller ice shelves and ice tongues in the Amundsen and Bellingshausen seas (Fig. 1b) provide buttressing that impedes the seaward flow of ice and stabilizes marine grounding zones (Fig. 2a). Despite their thickness (typically about 1 km near the grounding line to a few hundred metres at the calving front), a warming ocean has the potential to quickly erode ice shelves from below, at rates exceeding 10 m yr−1 °C−1 (ref. 14). Ice-shelf thinning and reduced backstress enhance seaward ice flow, grounding-zone thinning, and retreat (Fig. 2b). Because the flux of ice across the grounding line increases strongly as a function of its thickness15, initial retreat onto a reverse-sloping bed (where the bed deepens and the ice thickens upstream) can trigger a runaway Marine Ice Sheet Instability (MISI; Fig. 2c)15, 16, 17. Many WAIS grounding zones sit precariously on the edge of such reverse-sloped beds, but the EAIS also contains deep subglacial basins with reverse-sloping, marine-terminating outlet troughs up to 1,500 m deep (Fig. 1). The ice above floatation in these East Antarctic basins is much thicker than in West Antarctica, with the potential to raise GMSL by around 20 m if the ice in those basins is lost13. Importantly, previous ice-sheet simulations accounting for migrating grounding lines and MISI dynamics have shown the potential for repeated WAIS retreats and readvances over the past few million years18, but could only account for GMSL rises of about 1 m during the LIG and 7 m in the warm Pliocene, which are substantially smaller than geological estimates.”

I said it before. Including the details. So the evidence was clear, and out there. The optimism (it will take 5 centuries for 50 feet of sea level rise) is not supported by evidence. Actually collapsing channels coming from inverted rivers running up on the bellies of ice sheets are now obvious on satellite pictures and collapse of major ice shelves is going to be a matter of years, not centuries.

But science is made by tribes and these tribes honor the gods (of plutocracy) who finance them, and their whims. So they don’t want to make their sponsors feel bad. So they say unsupported, optimistic stuff, contradicted by a first order analysis.

Science is good, metascience, better. Metascience includes the sociological reasons which explain why some scientists will take some “facts” for obvious (although, coming from another sociology, they are not).

Deep in the Nature paper, in the quote above, or in four drawings and graphs of future sea level rise, one can find projections according to what various models “predict”… 130,000 years ago (!) The “Old Physics” model predicts one meter rise of the sea (this is the official UN maximal prediction for 2100). The new model, again starting with the present conditions, predict more than a six meter rise (!) This is a case of metascience playing with sea level.

This way, the authors of the paper will be able to say, one day: we told you so. While at the same time not irritating their sponsors now (because to understand what they are really saying takes quite a while, and has to be understood as tongue in cheek, when they pretend to apply the analysis to 130,000 years ago… What they really mean is six meters now, not just one meter… Bye bye Wall Street. Punished by its own instruments…)

The question is not whether we will be able to avoid a twenty meter sea level rise: that’s, unbelievably, a given (barring unforeseeable, yet imaginable technological advances to extract quickly a lot of CO2 from the atmosphere). The question is whether we will avoid a 60 meter rise.

Patrice Ayme’