Tuesday, 17 November 2009

Greenland ice melt: Waterworld? Not....

Article from the BBC on 12th November I heard on BBC Radio international (675 AM in Hong Kong) said that they ice sheet was melting at an accelerating pace and if it all melted, it would raise global sea levels by 7 metres.
I thought this was strange from two angles: first, the common sense angle.  It just didn’t sound right to me.  Second, I had just seen a video of an expert from the National  Oceanic and Atmospheric Administration quoted on a greenie website.  Asked what would happen if all the ice caps in the world – Greenland, the Arctic, Antarctica and all the glaciers –  were to melt, he said that the world oceans would increase by about 6 metres.  So, how could the melting of Greenland alone add seven metres just by itself.

I did a quick back of the envelope calculation.  The area of the world’s oceans is around 361 million square km.  So, to raise the sea levels by one metre would need 361 million cubic kilometres of water.  The area of Greenland is around 2.2 million square km.  Let’s assume it’s all ice (it’s not).  Ice is about 9% less dense that water, so that it takes about 1.09 cu metres of ice to create one cu metre of water.  That would mean that for Greenland’s ice to create 361 million cu km of water, the ice cap would need to be 1,386 km high.  It’s average depth, is only around 3 kilometres at the deepest estimates.  So the story of seven metres rise in the is out by a factor of  about 462. 
This is not to deny the danger of global warming and melting ice caps.  But it does seem to be of a style of the global warming alarmists: exaggerate the dangers, to gain public attention.  In this case exaggerate by 46,102.05%. (satire alert: spurious accuracy deliberate…).
In fact the exaggeration is greater since not all of Greenland’s area is ice, and some of it is sea ice.  But even assuming it’s all ice and all on land (the only ice which will actually raise sea levels when melted), then the actual increase sea level by the melting of the entire Greenland ice sheet – by my admittedly rough back of envelope calculations – is about 0.0165 metres, 1.65 centimetres, or about 0.65 of an inch.  That’s not seven metres, but less than an inch….
Maybe I’ve gone wrong here somewhere, and if so, let me know: fu.saisee@gmail.com
I also don't quite get their figures on the actual rise in sea levels; they don't seem to gel with some other figures I've seen, but will have to look at that later...
Postscript: I have, of course, made a schoolboy howler of an error, by incorrectly using cubic metres instead of cubic kilometres.  Allowing for that error, the figure of 7 metres rise in the sea level from a full melting of Greenland is about right.  My bad.  (where on earth did that phrase come from??).  Meantime, I've read somewhere that even during the last major warming periods Greenland did not in fact melt, pace those stories of Vikings tending cattle on a green land.