Environmental Engineering Reference
In-Depth Information
generates a negative feedback loop because clouds refl ect much of the
incoming solar radiation.
Possible changes in ocean currents create another uncertainty in heat
transfer. Quite small changes in the transport of heat or salt can have
large effects on surface temperature, and ultimately on climate. Ice, for
instance, seems to be moving at an increasing rate out of the Arctic
Ocean and moving both east and west of Greenland. Reduced sea-ice
cover in the Arctic might also increase the infl ux of warm Pacifi c waters
through the Bering Strait between Russia and Alaska.
Greenland
In addition to the uncertainties created by feedback loops,
climatologists have discovered that they are unable to determine accu-
rately how fast the ice in Greenland and Antarctica will melt. The ice
cap on Greenland contains 800 trillion gallons of water, about the same
amount of water as the Gulf of Mexico, and it seems that cracks are
forming in the ice as it moves downslope to the ocean.
19
Millions of
gallons of water from the melting surface of the ice fl ow into the cracks
and downward to the contact between the base of the ice and the rock
beneath. This lubricates the contact, allowing the ice above to increase
its rate of fl ow toward the ocean. The ice cap cannot be thought of as a
single block of ice that is melting under the summer sun.
As a result of the growing cracks and lubrication, Greenland is losing
48 cubic miles of ice each year, double the rate of fi ve years ago.
20
One
glacial tongue had a surge toward the sea that was measured to be 3
miles in 90 minutes.
21
One Greenland glacier puts enough freshwater
into the sea in one day to provide drinking water for a city the size of
New York or London for a year.
And the rate may increase even more, and not only because of the
vertical cracks in the ice. Most of Greenland's ice mass is actually below
sea level. The weight of billions of tons of ice over tens of thousands of
years has depressed the rock beneath it so that the ground beneath the
ice is actually a big shallow bowl. It is now fi lled with a subglacial melt-
water lake that is 1,500 feet deep.
22
Seawater may soon fl ow in under
the ice, effectively “fl oating” off most of the glacier into the ocean,
rapidly accelerating its collapse. The current estimate of sea level rise of
0.1 inch per year may be an extremely poor predictor of the rise in the
near future, but even at today's rate of climate change, the UN estimates
that 25 to 50 million people in low-lying areas will have been displaced
by 2010.
23
According to the UN report, “Societies affected by climate
change may fi nd themselves locked into a downward spiral of ecological
