Wednesday, June 24, 2009

The Slow Melt of Antarctica

A little while ago the New York Times' Andrew Revkin had a post about a study by David Pollard and Robert DeCanto that found that even in the worst case, global warming would lead to a collapse of the Antarctic ice sheet much more slowly than was previously thought. That process is illustrated in this video:

Says Revkin:
The bottom line? In this simulation, the ice sheet does collapse when waters beneath fringing ice shelves warm 7 to 9 degrees Fahrenheit or so, but the process — at its fastest — takes thousands of years. Over all, the pace of sea-level rise from the resulting ice loss doesn’t go beyond about 1.5 feet per century, Dr. Pollard said in an interview, a far cry from what was thought possible a couple of decades ago. He, Dr. DeConto and other experts on climate and polar ice stressed that when Greenland’s possible contribution to the sea level is added, there’s plenty for coastal cities to consider. But for Greenland, too, some influential recent studies have cut against the idea that momentous coastal retreats are likely anytime soon.

Over all, the loss of the West Antarctic ice from warming is appearing “more likely a definite thing to worry about on a thousand-year time scale but not a hundred years,” Dr. Pollard said.
Well, that's good. I have to say, though, that rising sea levels have never seemed like the scariest threat from global warming. Terrible for Bangladesh, yes, and a few other places around the world; but something that, even on the scale of hundreds of years, let alone thousands, is something to which we could adapt. The collapse of ecosystems, the desertification or aridification of productive agricultural land, and the resultant famine, mass migrations, and political instability, though - those processes will play out in a much faster, unpredictable, and destructive way.


Gus said...

That still amounts to a significant sea level rise in a century. Enough to seriously impact coastal areas, where the bulk of the earth's population resides, not just Bangladesh. Can we adapt to that? Sure, but the number of people living on barrier islands in spite of repeated hurricanes should show just how unwilling people are to do what is necessary to adapt. Add to that the amount of expensive high rise real estate that could be threatened and the cost could be significant.

Gus said...

I can't wait to see the "global warming is a hoax" folks use this study to prove that there is no threat from global warming, even though it proves no such thing. It is also important to note that this is a simulation - as are pretty much all the studies of the potential effects of global warming. The critics are right when they say simulation is rife with potential error, but one simulation is much more likely to be wrong than many simulations. That's the point of simulation, to do it many, many times and see what the most common result is.

Andrew said...

During the Holocene Climatic Optimum, when temperatures were warmer than they are now for several thousand years, there is no evidence that Florida or Bangladesh were underwater. Why should we believe this would change absent major changes in geology?

On the other hand, on the scale of geologic time, the sea levels are thought to have been generally much higher than today, obviously without any help from humans. This would put human efforts to "stop" sea level rise on par with spitting into the wind.

Gus, you seem to be saying, damn all that, I know the threat of sea level rise is true because my computer told me so! That point of simulation is to model something prior to it occurring, and then using its occurance to validate or adjust the simulation and its parameters. Clearly, that cannot be done with future contingent events.

Chachy said...

From the Wikipedia entry on the Holocene Climatic Optimum:

In terms of the global average, temperatures were probably colder than present day (depending on estimates of latitude dependence and seasonality in response patterns).

Of 140 sites across the western Arctic, there is clear evidence for warmer-than-present conditions at 120 sites. At 16 sites where quantitative estimates have been obtained, local HTM temperatures were on average 1.6±0.8 °C higher than present.

By comparison, global warming is likely to lead to a 5C global temperature rise, and closer to 10C in the Arctic.

Gus said...

Actually Andrew, I meant to say nothing of the sort. What I was trying to say was that just because this study's computers told them sea levels won't rise is not reason enough to ignore all the computers that say sea levels will rise.

I argue only that climate change is complicated enough that drawing specific, detailed conclusions based on a single study is unwise.

As for the point of simulation, a lot of simulation is done today in fields, like climate change, that cannot be validated based on real world data. The point here is, as I said before, to be able to test a large number of possible scenarios, and to expand on what I said before, not just to see what the most common result is, but to examine a number of possible results and make decisions that are informed by all of those results, but most importantly, not by just one result.

Gus said...

Does that last sentence count as a run-on? My thesis adviser kept telling me to string more of my ideas together, and I'm pretty sure the final document was rife with run-ons.

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