80 m is about the maximum, because there's about 7 m in Greenland and the West Antarctic Ice Sheet each, and about 60 or so in the East Antarctic Ice Sheet. Once that's molten, there's nothing left to melt.
While I find Hansen's arguments somewhat speculative with regards to sea level, and rereading the relevant section in the paper, he does in fact point out all the relevant provisos and uncertainties, I do definitely think the analogy with past temperatures and sea levels is convincing enough that we need to consider relatively fast melting a realistic possibility.
When I got a comment from Fergus, it suddenly struck me that I did know a very good example of an artificial hill that could serve as an example for dike building:
That's the Sophienhoehe. It's located right next to where I grew up. My parents' house is located roughly where the big trees at the right of the picture are.
http://en.wikipedia.org/wiki/Sophienh%C3%B6he
The Sophienhoehe averages a height of 200m, it's an artificial hill created within about 10 years in the 1980's. The open cast mine next to it has the lowest surface point in Europe at 293 m below sea level. The top of the Sophienhoehe is at 290 m above sea level and therefore 583 m above the bottom of the pit.
http://www.rwe.com/generator.aspx/rwe-power-icw/presse/downloads/property=Data/id=229654/wandern-sophienhoehe.pdf
This map indicates that its maximum length is about 6 to 7 km, and perpendicular to that it ranges from 1 km to 4 km.
A few years back I sent an email to Rheinbraun asking about their energy consumption compared to the energy in the coal they get out, and the answer was something around 3%. Not all of that energy is for the digging equipment, but even assuming it all were, this does not in fact seem large for the type of hill they've put up in just a few years.
The equipment Rheinbraun use for digging is most impressive:
http://www.oih.rwth-aachen.de/~hendrik/bagger.html
The digging machines can move 240,000 m3 of soil per day, weigh 13,500 metric tonnes and are 225 m long and 96 m high. They require 16.56 MW of power.
This is a picture of the open cast mine:
Assume an absolutely extreme scenario, 80m of sea level rise. A 200 m high, 3 km thick dike would even hold that.
Of course, we aren't likely to see that any time soon, 5 to 10 m sea level rise by the year 2300, however, is quite a realistic prospect. I just don't see us allowing cities like New York or London to be flooded when we've got 300 years.
1 comments:
Its going to depend entirely on where in the world you intend to build, and its vulnerability to storm surges, TCs and tsunamis, but in principle, one can imagine a 'ring' of dikes around key strategic locations - like London. If such a project were to be undertaken, it would require a dike aprroximately 250km long and, at the lowest point of the land, about 15-20 metres high, to protect against a sea level rise of 1.5-2 metres + storm surges.
Whilst this might work, the experience of New Orleans should be a salutary one; such tools are only as strong as their weakest link...
There is also the question of how you might 'dike up' the entire Delta that forms a large portion of Bangladesh, or the Chinese coast, or Florida. Such projects may be feasible, but this does not in itself make them viable. In the end, abandonment ans resettlement is likely to prove the most often-taken option, once the first couple of avoidable disasters have already happened, and we get rise to the consequences of inadequate preparation.
I suspect, having said all this, that dike building programmes are already in the pipeline in several countries.
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