by Gaius PubliusWe learned recently that the West Antarctic ice sheet is collapsing irreversibly. The Guardian in May:
The collapse of the Western Antarctica ice sheet is already under way and is unstoppable, two separate teams of scientists said on Monday. The glaciers’ retreat is being driven by climate change and is already causing sea-level rise at a much faster rate than scientists had anticipated.
"Irreversible ice sheet collapse" is cause for much concern. Thanks to the always valuable Greg Laden, we find this handy USGS table of how much water is stored as ice around the world: Table 1. Estimated potential maximum sea-level rise from the total melting of present-day glaciers. [Modified from Williams and Hall (1993). See also http://pubs.usgs.gov/fs/2005/3055/.] Location Volume (km3) Potential sea-level rise, (m) East Antarctic ice sheet 26,039,200 64.80 West Antarctic ice sheet 3,262,000 8.06 Antarctic Peninsula 227,100 .46 Greenland 2,620,000 6.55 All other ice caps, ice fields, and valley glaciers 180,000 .45 Total 32,328,300 80.32Numbers to keep in mind — 80 meters of sea level rise (SLR) is almost 90 yards, more than 260 feet. Of that, 8 meters (26 feet) is stored in the West Antarctic ice sheet, the one that's collapsing first.A note though on sea level rise from melting ice. It's not as simple as a converting a volume of ice to a volume of water and calculating the increase in height. That water will also (a) increase in temperature, which causes its volume to expand; and (b) rise higher in the mid-latitudes than in the poles, since the strong gravitational pull of the collapsed ice sheets, which keeps water near the poles, will be gone. Not only that — (c) if you live, say, five feet above sea level but near the water, and the sea rises, say, three feet, you're still not safe. The rising water will lap at and erode the land under you. At some point, you'll have to move further from the shore — move your home, move your city. How much further? If the seas are constantly rising, as they will do in a "business as usual" (BAU) carbon emissions scenario, you'll never know. (Oops.) If you think that's bad news for your vacation home, imagine the problem for New York City.What's Rate of Collapse in West Antarctica?So we know what's collapsing — the West Antarctic ice sheet — but we weren't sure how fast. Now we're learning more about the rate. From Chris Mooney and Joby Warrick, writing in the Washington Post:
[N]ew evidence is causing concern that the collapse could happen faster than anyone thought. New scientific studies this week have shed light on the speed and the mechanics of West Antarctic melting, documenting an acceleration that, if it continues, could have major effects on coastal cities worldwide.Twin papers this week show that the rate of ice loss from West Antarctica is increasing — with the acceleration particularly pronounced in the past decade — and also why this is happening: Warmer ocean waters are pushing up from below and bathing the base of the ice sheet.The findings add to a growing body of evidence suggesting that the effects of climate change are outpacing scientific predictions, driven in part, scientists say, by soaring levels of greenhouse gases in the atmosphere.
Part of the problem is that in general, almost every climate event is happening faster than anyone expects. I've called that being "wrong to the slow side." In this case, the reason scientists have been wrong — under-estimating the ice melt rate — is that the dynamics of ice sheet collapse were little understood before now. Part of these ice sheets, called "ice shelves," stick out over the water. Not only is warmer air melting the ice from above. Warmer water is melting it from below.And once this process starts, warm water can creep onto the land under the ice as well — between the land mass and the ice on top of it — further undermining the ice. These two diagrams from a larger one in the Post article show what I mean. The first shows a stable glacier (click to enlarge): And the second, a glacier being undermined from beneath:What's not shown here is that in many areas, the part of the land mass ("continental shelf") that's near or below sea level, yet sealed off by ice, extends quite far inland. Think of these as canyons or deep river valleys. Once water from the ocean enters these canyons it can erode a lot of land-based ice as well. How Fast Could Sea Level Rise?To answer that question, I'll give two estimates, and an offsetting view. First, from the article (my emphasis everywhere):
So how fast could the loss of West Antarctica unfold? Velicogna’s co-author, Eric Rignot of UC-Irvine, suggested that in his view, within 100 to 200 years, one-third of West Antarctica could be gone.
That implies a sea level rise, per the table above, of almost three meters, or nine feet. Next from James Hansen and his work with paleoclimate, the study of climate hundreds of thousands of years ago (quoted here):
BAU ("business-as-usual") scenarios result in global warming of the order of 3-6°C. It is this scenario for which we assert that multi-meter sea level rise on the century time scale are not only possible, but almost dead certain.
In the underlying paper (pdf) Hansen asserts that sea level rise will likely be non-linear and suggests a doubling every ten years:
Paleoclimate records include cases in which sea level rose several meters per century, even though known natural positive forcings are much smaller than the human-made forcing. This implies that ice sheet disintegration can be a highly nonlinear process.We suggest that a nonlinear process spurred by an increasing forcing and amplifying feedbacks is better characterized by the doubling time for the rate of mass disintegration, rather than a linear rate of mass change. If the doubling time is as short as a decade, multi-meter sea level rise could occur this century.
The graph in the paper shows sea level rise of five meters by 2100 at a 10-year-doubling rate of change: \Fig. 7. Five-meter sea level change in 21st century under assumption of linear change and exponential change (Hansen, 2007), the latter with a 10-year doubling time. And the offsetting view? The IPCC, among others, are much more conservative. From the article:
The findings from West Antarctica could call into question one principal finding from the latest report of the United Nations’ Intergovernmental Panel on Climate Change (IPCC), considered to be the world authority on global warming. In 2013, the panel put its high-end projection for likely global sea-level rise, by the year 2100, at a little more than three feet.
So, sea level rise of less than three feet by 2100, or up to 15 feet? Place your bets. And while you're at it, place your bets on the year the Arctic goes ice-free in the summer. Here's the bet the IPCC placed, using its models (click to enlarge):\ The blue band shows the range of what the models, 13 of them, predicted. The red line is "reality," what actually happened. By 2012, ice loss was almost as great as the mean loss predicted through the end of the century. As usual, predictions were "wrong to the slow side." In the case of Arctic ice loss, very wrong. Not Impossible; Just UrgentThis is not doom and gloom, and it's not a hard task physically. A WWII-style crash conversion (described here) could get us carbon-free in about 10 years — and I'm told by people in the renewables industry that, whatever the politics, the target rate is not technically impossible. But that conversion, as needed as it is, will have to be forced. How we get there is a subject for another time, and I will return to it.But if you throw out any fantasies you may have about unicorns and the "free market" providing a solution, and you assume that at some point people will be so worried (or panicked) that they'll demand government fix the problem (even Tea Party voters will do that, or especially them) — then you know where the answer is. David Koch and ilk will not back down; but they can be made to — for example, by a country that suddenly sees Miami real estate become worthless and uninsurable in one storm-caused Night of the Krell.See the end of this post for my six prescriptive bullet points. When the populace wants it (and believe me they will), government will be empowered to act. Our job is to make that act an effective one. Stay hopeful.GP
