Thursday, 25 June 2015

Can I sell you a mountain?

Sure, sea level is rising, but it was only 1.7 mm/year in the 20th century. And it's only 3 mm/year now - 300 mm by 2100. That doesn't sound much, does it?

Though, of course, that assumes there's no further increase in the rate. In fact increasing greenhouse gas emissions make an increase almost certain so it might be 500 mm by 2100.

So how about the long-term?  If we keep the global temperature rise below two degrees we can expect 400 mm from loss of mountain glaciers, 800 mm from ocean expansion and 3.3 m from the melting of the West Antarctic ice sheet. That's 4.5 m in total. That's the same as the largest tidal rise on the Essex coast and, obviously, it would add to the tidal rise.

These numbers are based on very cautious treatment of the melting of glaciers and the Antarctic ice. And that's a problem because we keep finding new mechanisms that allow the ice to melt much faster. For instance, the great Antarctic glaciers flow to the sea where they generate vast ice sheets. But the sheets are breaking up (which does not raise sea level) and this allows the glaciers to move much faster (which does).

There are a lot of uncertainties here but they aren't comforting ones. They boil down to two questions:
  1. Have we already passed the points of no return for any of the Greenland and Antarctic glaciers?
  2. How hot will the planet get? (We're currently on course for 4-6 degrees of warming.)
  3. How fast will we reach maximum sea level?
New Scientist estimates that four degrees of warming would produce 20 m of sea level rise. 

How much do mountains cost these days?

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