The Ice Cages Melt

The World Without Us —Alan Weisman— (Chapter 16: Our Geologic Record)         180 miles northeast of Yellowknife, Northwest Territories, Canada: a very round hole half a mile wide and 1,000 feet deep. A dried-up lake.       North of the 60th parallel, Canada contains more lakes than the rest of the world combined. Nearly half of Northwest Territories isn't land at all, but water.       Ice ages gouged cavities into which ice-bergs dropped when the glaciers retreated. When they melted, these earthen kettles filled with fossil water...       Evaporation is slow in cold climates, little more precipitation falls here than in the Sahara.         But: as the permafrost thaws around these kettles, glacial water held in place by frozen soil for thousands of years is seeping away.         In the Eocene, today's lichen-covered tundra was coniferous forest.         One of the oldest mammal species on Earth still lives here, a Pleistocene relic that managed to survive because it was extraordinarily equipped to brave weather that ice-age humans preferred to escape: the musk ox.         The pelage of the musk ox, known in Inuit as qiviut, is the warmest organic fiber known. It makes them impervious to cold but became their downfall when they were all but exterminated by hunters in the early 20th century who sold their hides in Europe.         If too much of the permafrost is undone, it would thaw deeply buried ice that forms crystalline cages around methane molecules.          An estimated 400 billion tons of frozen methane deposits, known as clathrates, lie a few thousand feet beneath the tundra, and even more are found beneath the world's oceans.         That very-deep-freeze natural gas is estimated to equal all known conventional gas and oil reserves. But it is so dispersed no one has come up with an economical way to mine it.         If it all floats away once the ice cages melt, that much methane might ratchet global warming to levels unknown since the Permian extinction, 250 million years ago.