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The Sea Level Rise Mystery

Twenty inches per decade -- that's the estimate of how rapidly the oceans rose in the last interglacial period about 121,000 years ago, in research appearing in Nature. That's eight feet over 50 years, in a world just 2°C warmer than we are today.

Not good.

But one little detail bugs me: while we can make educated guesses as to what triggered the sea level increase (glacial melts, presumably), there's no way of knowing from the fossil evidence when that trigger happened. That is, how long between the prehistoric Antarctic ice sheet collapse (for example) and the resulting surge of ocean water actually making it to the rest of the world?

It turns out that, due to some major currents and the sheer mass of the ocean, dumping megatons of ice (or rock, or whatever) into one part of the sea doesn't make the whole world's sea level pop up immediately. It will, eventually, but it takes time, potentially decades -- or even centuries.

That was the conclusion of a 2008 article in the Journal of Geophysical Research modeling sea level increases resulting from Antarctic and/or Greenland glacial melts.

According to this research, it takes a surprisingly long time for a massive glacial melt to actually increase sea levels outside of the initial melt zone. Here's the relevant quote from the New Scientist article at the time:

... the majority of Greenland's meltwater will stay in the Atlantic Ocean for at least 50 years, causing sea levels here to rise faster than expected. "The Greenland ice cap is much less of a threat to tropical islands in the Pacific than it is for the coasts of North America and Europe," he says. [...] Antarctic meltwater could be prevented from reaching much of the world for centuries due to strong currents in the Southern Ocean, says Stammer.

Here's the link to my summary, with graphics, from last year.

Basically: meltwater from Greenland takes a decade or so to hit the western Atlantic (i.e., US East Coast), and doesn't notably affect the Pacific at all in the 50 year model run. Meltwater from Antarctica -- although much greater in volume -- never substantially leaves the Antarctic Ocean for the same 50 year model.

Obviously there would be eventual equilibrium, so this study doesn't contradict the paleo results of rapid sea level increases -- once the surge gets to a region, at least. But it does make the situation more complex. If those of us with our hair on fire about global warming make what we think to be well-substantiated claims about sea level increases coming from temperature increases, and nothing (seems to) happen, we'll be accused of "crying wolf," lying about the danger just to get our pet socialiberatheislamofascist projects through.

But here's the problem: I haven't seen any follow-up work to the JGR article. Nothing backing it up, nothing rejecting it, nothing criticizing the model... It's like this study just kind of got ignored. Anyone out there know anything more?


While Stammer's article was submitted in 2006, it wasn't actually published until Dec 2008, so give it time.

Still, a google search for 'stammer' and 'meltwater' provides a hit with at least one PhD thesis proposal

The water has to go uphill for about 21 kilometres dew to bulge around the earth's equator. So from Greenland to the other oceans it has to accelerate to go over the top and then decelerate while it flows back in the sought Atlantic and the other oceans. What happens to the currents in the oceans when Greenland melts and simultaneous de north pole ice sheet is unknown. It could flow throw the Bering street in the pacific. Overflown the tundra's in north Russia. Just a thought, no proof or expertise.

Poking around with Google eventually yielded this abstract from Nature Geoscience (March 2009), which seems relevant. (See also a recycled press release here.)

From the abstract (which is all I can read, as the article itself is behind a Nature paywall):

... [we] find a rapid dynamical rise in sea level on the northeast coast of the United States during the twenty-first century. For New York City, the rise due to ocean circulation changes amounts to 15, 20 and 21 cm for scenarios with low, medium and high rates of emissions respectively, at a similar magnitude to expected global thermal expansion. Analysing one of the climate models in detail, we find that a dynamic, regional rise in sea level is induced by a weakening meridional overturning circulation in the Atlantic Ocean, and superimposed on the global mean sea-level rise.

It sounds like this is a different (additional?) effect from that discussed in the Stammer article, though I can't be sure.

I agree with Tony Fisk, though -- it's definitely too early to claim that this is being ignored.

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