[新聞] Seasonal Factor Seen in Melting and Ice Shifts in Greenland
來源媒體或網址: The New York Times
Seasonal Factor Seen in Melting and Ice Shifts in Greenland
By ANDREW C. REVKIN
One of the most vivid symbols of global warming is the torrents of melt
water that drain from the lakes that form each summer on Greenland’s ice
sheet.
Recent studies have shown that this water, which flows deep into the ice
through natural drainpipes called moulins, allows the ice to slide faster
over bedrock toward the ocean. And the faster the ice flows, the faster sea
levels rise. But a Dutch study using 17 years of satellite measurements in
western Greenland suggests that the movement associated with the meltwater is
not as rapid as had been feared. The acceleration appears to be a transient
summer phenomenon, the researchers said, with the yearly movement actually
dropping slightly in some places.
“The positive-feedback mechanism between melt rate and ice velocity,” says
the report, published Friday in the journal Science, “appears to be a
seasonal process that may have only a limited effect on the response of the
ice sheet to climate warming over the next decades.”
Greenland is still losing more ice through melting than it gains through
snowfall, other measurements show.
The study was led by Roderik S. W. van de Wal of the Institute for Marine
and Atmospheric Research of the University of Utrecht. He said the overall
slowdown might be because of changing plumbing deep inside the ice. The study
builds on earlier work also showing a limited overall change in ice flow from
the surface melting.
The authors and independent experts familiar with the research stressed that
the findings did not preclude the possibility that more widespread surface
melting could eventually destabilize big areas of Greenland, the world’s
second largest ice storehouse. Richard B. Alley, a glaciologist at
Pennsylvania State University, said that big lakes were likely to form as
areas of melting spread inland, and that this could unlock new ice regions to
start sliding more.
But Dr. Alley and other experts said the new study showed that it was
unlikely that Greenland’s ice had already become destabilized in ways that
could cause a surge in sea levels.
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