From NASA Educational
On Thin Ice
02.12.04
In the summer of 2002, graduate student Derek Mueller made an unwelcome discovery: the biggest ice shelf in the Arctic was breaking apart. The bad news didn't stop there. Lying along the northern coast of Ellesmere Island in northern Canada, the Ward Hunt Ice Shelf had dammed an epishelf lake, a body of freshwater that floats on denser ocean water. This epishelf lake, located in Disraeli Fiord, was host to a rare ecosystem, and it was the largest and best-understood epishelf lake in the Northern Hemisphere. When the Ward Hunt Ice Shelf fractured, the epishelf lake suddenly drained out of Disraeli Fiord, spilling more than 3 billion cubic meters of fresh water into the Arctic Ocean.
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Changes observed in the Arctic confirm climate model predictions. "We know from global circulation models -- the results of which are broadly accepted among the polar climate and global climate community -- that if global change is occurring, the effects will be felt first and amplified in the polar regions, particularly the Arctic," said Jeffries. "We've seen changes in the Arctic, and in recent years, the changes seem to be occurring faster."
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Changes observed in the Arctic confirm climate model predictions. "We know from global circulation models -- the results of which are broadly accepted among the polar climate and global climate community -- that if global change is occurring, the effects will be felt first and amplified in the polar regions, particularly the Arctic," said Jeffries. "We've seen changes in the Arctic, and in recent years, the changes seem to be occurring faster."
Vincent agrees. Prior to the Ward Hunt Ice Shelf breakup, his team monitored Disraeli Fiord for five years. Though he had observed gradual decreases in the lake's fresh water, its sudden disappearance caught him off guard. "I think it underscores a fundamental problem we have in climate change research," he said. "Climate change models usually predict gradual, continuous change, but real-life impacts are not continuous. Changes can be relatively small, and then suddenly you can move to a new threshold. This ice shelf survived 3,000 years of human civilization, but now it's gone."
How much change can be attributed to human activity is difficult to estimate. "We know the climate can vary on many different time scales due to natural processes," said Serreze. "But when we look at the longer-term record of paleoclimate information, the warming we're seeing does appear to be very unusual. Carbon dioxide concentrations in ice cores today are probably the highest they've been in 400,000 years. There's a growing consensus between the things we're observing and climate model projections of change. I'm still a fence-sitter, but I'm leaning more to the side of human causes for at least some of what we're seeing."
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