I am full of sh*t. I don't think I transfered a number into to the correct units. But I still get a bigger number than logical for the amount of ice needed in Greenland. Here's how I figured it using Oxford Atlas of the World, Tenth Edition, Published 2002 as my reference.

Area of Greenland is 838,999 Sq Miles
Water surface of earth is 57,000,000 square miles

V=a^2 X H Right?
20 feet = .0037878 miles

area of the oceans X Height of the added sea level
57,000,000 X .0037878 = 215,904.6 cubic miles.

Volume of added sea level divided by area of Greenland
215,904.6 / 838,999 = .2573359 (This should give a mean thickness of the ice required in Greenland to raise the oceans 20' in miles)

5280 X .2573359 = 1358.73 ft.

Refering to my atlas again: "Greenland is the world's largest island. Settlements are confined to the coast, because an ice sheet covers four-fiths of the land." Four fiths of the land, so 80%, close enough. So the ice that is there would have to be 20% thicker than our mean thickness. So 1358.73 / .8 = 1698.41 ft. So all of Greenland's ice is this thick?

Thats alot of ice. I'm sure its a mile thick in places, but it looks like most of Greenland is inside the Arctic Circle. A few degrees just doesn't matter up there. This is the best that a self employed construction worker, high school drop out can figure. Sorry for incorrect number before but I think I forgot to change 20 feet into a fraction of a mile. Question everything. Whether it comes from the right or left. And yeah, I'm not figuring in the added area from the slope of the shorelines, the required ice would be much more. Plus this is figuring ice at a standard volume, not factoring in expansion when water freezes which would also increase the amount of ice required in Greenland to raise the ocean 20 feet. This also does not take into account that as the depth is increased around the surface of a sphere more volume is required to add depth because the bigger the sphere the more area, also requiring more ice to raise ocean levels a given amount. Figuring that out is well beyond my 10th grade education. Maybe my math is incorrect again, prove me wrong. Educate me. Tell me I'm just another dumb redneck, enjoy!