Saturday, February 02, 2008

the big lurch: 213 ft or 65 m


The February print edition of Scientific American has an article by Robin E. Bell, director of the Center for Rivers and Estuaries at Columbia U's Earth Institute, on an emerging reality in the context of climate change. The article, "The Unquiet Ice," in Sci Am 298.2 (2008): 60-67, in the public domain as a stub, is the latest word on what's happening.(1)

Here's an attempt to parse the information and make sense of it. There are three large ice sheets on the planet: one in the north, two in the south. The northern sheet is the chunk that sits on top of Greenland. The two southern pieces are the West Antarctic and the East Antarctic ice shields, with the western smaller than the eastern. The West Antarctic shield rests on the edge of the south polar continent and on top of islands. The East Antarctic ice shield sits on land. All in all, the three shields hold 99% of the world's ice.

But now they're poised to lurch. The sheets are miles thick and sit on rock. Weight and friction creates melt-water between ice and rock. There's a network of lakes and rivers underneath. The shields are glaciers, naturally, so they slowly grow, moving from the interior to the coasts, where they break into bergs and melt off. Their growth is fueled by snow fall. In the Antarctic, in particular, the coastal melt is held in check by ice aprons -- as the shields edge out beyond dry land, their rims float on the sea, and these swimming aprons are in the way of ice piling up behind. The ice queuing up first needs to push the aprons out of the way before it'll be its turn in the drink. As the aprons break off, new ice moves in. That's how it has always been. New now is this:

As the ocean warms, the aprons break up quicker. Since they function like stoppers in a bottle, uncorking the bottle makes the ice queuing up behind the apron flow freely. Broken-up aprons means uncorked bottles. The more the apron tatters, the quicker the ice flows; the quicker it flows, the faster it pushes the tattered apron out of the way. That's positive feedback 1.

As it gets warmer, there's more melt-water on top. The water trickles through cracks in the ice down to the rock. There it bloats the ancient network of rivers and lakes underneath the ice. The rock-ice interface is getting wetter. Friction decreases that would otherwise slow the moving floes. Stability decreases that would otherwise hold the sheet in place. The more slippery the interface, the faster the sheet's motion; and the faster it moves -- smearing out rivulets and ponds into wider, smoother planes -- the slicker the interface gets. That's positive feedback 2.

Add to this the albedo problem.

The more ice melts into the water, the darker the surface becomes, turning from snow white to ocean blue. The more the surface darkens, the less sun is bounced back into space. The less is reflected, the more is absorbed. The more heat is absorbed, the more ice melts into the water. That's the loop that cinches it, that promises a domino effect -- positive feedback 3.

So the new information suggests that the polar situation is becoming unbalanced. The editors at Scientific American, usually a staid and sober lot, use the adverb "catastrophically" in the header of the article. The problem is that things may go fast. The Larsen B ice shelf that broke off the Antarctic Peninsula in 2002 slid into the water and disintegrated in five weeks, from January 31 to March 7. Glaciers move slowly. Avalanches don't.

A lurch of the sheets might be a matter of months not years. A sea level rise would be a matter of days not months. The cause of the sea level rise is not ice slowly melting, but ice instantly displacing water -- the ice that drops into the water had been on land before. The water displaced by all the new bergs has no way to go but up. How much it'll go up depends.

P. 63 of the article has three maps of Florida. If the West Antarctic shield lurched, Florida would be stubbier. If the Greenland sheet leaked out of the uncorked bottle, stubby Florida would be on a diet. If the East Antarctic shield lurched, Florida would shrink into a scatter of keys north of Orlando and one island north of Panama City. The new U.S. coastline would be in Georgia.

Case 1 (West Antarctic) = 19 ft / 6 m sea level rise.

Case 2 (Greenland) = 24 ft / 7.3 m sea level rise.

Case 3 (East Antarctic) = 170 ft / 52 m sea level rise.

The sequence suggested by Scientific American is deliberate. The West Antarctic ice shield stands to let go first, since its base is the smallest (partly on islands). And it did let go before. The Greenland ice shield is already turning into a swiss cheese of watery sinkholes draining via tubular caves into the Atlantic -- didn't we all learn the new word "moulin" only a few months ago? The East Antarctic had been stable for tens of millions of years and would be the last to lurch, if at all. Lest someone accuse me of dramatizing the news or of insinuating a fallacy here -- tacitly assuming that the distinct shields would be interconnected such that if one goes, the others go -- kindly consider the albedo problem. Any shield that lurches melts. White surface turns dark blue. Ocean warms up. Warmed-up ocean eats the aprons of the other shields. So, yes, their fates are interconnected.

We might lose land. If and when all three shields let go, sea levels would rise 213 feet or 65 meters -- think Statue of Liberty up to her neck in water. There is no engineering solution for this. You can't build dikes or levees that high. You just have to call it quits and move to higher ground.

Half of us live within an hours' drive from the coasts. How many would have to move? New cities would have to be built. Old fields would be lost. More people on less land means hunger. Climate Change is already messing up Agricultural Productivity; that's last year's news. But with the Big Lurch, agricultural productivity will totally tank just when it needs to be jacked up. Paradoxically, the Big Lurch also means thirst, since the sea level rise will contaminate coastal fresh water supplies.

Another side-effect of the Big Lurch -- noted by a blogger on the SciAm site, and so far unchallenged -- would be seismic activity. Right now, there is a lot of ice sitting on the Earth's crust at the poles. That's heavy stuff. If it moves, the crust will bounce up. In this polar rebound, and with the rebound traveling along the crust, the Ring of Fire around the Pacific Plate might let go. There might be volcanic eruptions in the Americas, Indonesia, and the Pacific Rim. That would mean even more CO2. The airborne ash would mean a negative feedback loop, in cutting down sunshine, but even then, plant growth wouldn't exactly be helped with the darker skies. Plus, the air would stink.

We can't shop ourselves out of this one. Pulling a Gore -- buying new light bulbs and leasing a Prius -- won't cut it. Unfortunately, the quickest way to cut emissions would be to stop the economic clock. Climate change is a market failure of stunning proportions. It's Gaia's punishment for us being stupid enough to trust Adam Smith's invisible hand. Facing a post-capitalistic future would be scary. But did anybody really think that this sad consumerism, all bling, no soul, would, could, or should go on forever? And assuming we and the kids can surf through the worst, would it not be a relief when the ownership society is over? Would its collapse not free us to evolve to a saner existence? Getting there will be tough. But it will be greener on the other side.

What can the individual do?

Six words: Live small. Opt out. Think big.


(1) Bell's February 2008 paper is based on new data plus older studies, by Kohler in Nature 445 (2007): 830-831; Bell et al in ibid.: 904-907; Fricker et al, in Science 315 (2007): 1544-1548; and Bentley et al, UNEP Global Outlook 2007, 99-114 (part of a large pdf).


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