"00ZNB" <00ZNB@[EMAIL PROTECTED]
> wrote
> McCain Should Stick To Real Problems
>
> INVESTOR'S BUSINESS DAILY
Here is a real problem....
Greenland ice lakes drain at speed of Niagara Falls
19:00 17 April 2008
NewScientist.com news service
Mason Inman
Lakes on the surface of Greenland's ice sheet are draining through the
kilometre-thick ice and roaring to the bedrock with a flow rate exceeding
that
of Niagara Falls.
The worry has been that with further global warming such meltwater would
increase and have a catastrophic effect on the ice sheet, lubricating its
base
and making it slide quickly into the ocean. But a new study suggests that
the
meltwater's effect is not as strong as feared.
In the summer months, the surface of Greenland's ice sheet melts and the
water
pools on top, forming many lakes that are kilometres across. Researchers
knew
these lakes could drain quickly, but it wasn't clear exactly how they
drained
nor how fast.
Ice fracture
Sarah Das of the Woods Hole Oceanographic Institute, US, and colleagues
camped
out next to a 3-kilometre-wide lake in western Greenland. In July 2006,
their
seismometers picked up rumbles from the ice, then 30 minutes later the
water
started draining.
The entire lake was swallowed up in about an hour and a half. "The most
surprising thing was the speed," Das says. "I didn't think it would happen
that
fast." The scientists think the weight of the water created a fracture in
the
ice that then opened the entire one-kilometre thickness.
Summer rush
Once at the base of the ice sheet, the water seems to have drained away
within a
day. "It was either tapping into an existing drainage system or forming a
new
system" at the base of the ice sheet, Das says.
To get a broader view of how such water is affecting Greenland's ice, Ian
Joughin of the University of Wa****ngton, Seattle, US, led a separate study
using
satellite images and GPS measurements. His team assembled the first map of
the
movement of the ice sheet and glaciers in Greenland, and found that each
summer,
the ice sheets slid toward the ocean 50 to 100% faster than they did
during
the
rest of the year.
However, glaciers, which already flow much faster than the surrounding ice
sheet, speed up by less than 15% during the summer, according to the
study.
Nonetheless, the lubrication from the meltwater could make Greenland lose
from
10 to 25% more ice over the 21st century than if this effect was not at
work,
Joughin and colleagues estimate.
"The good news is that increased melting [with continued global warming]
doesn't
seem like it's going to cause a runaway effect like some people had
predicted,"
Joughin says.
Added lubrication
However, global warming does seem to be substantially speeding up glacier
flow
through other means, he argues, such as warmer oceans that are eating away
at
glaciers' feet.
"I agree that at present, the lubrication of the ice sheet margins by
meltwater
will have a substantial but not catastrophic effect," says Konrad Steffen
of
the
University of Colorado in Boulder, US.
But Steffen thinks that the meltwater could still speed up some glaciers
more
than it does others. He points to Greenland's so-called Dead Glacier,
stagnant
for decades until it recently became active, which speeds up by 80%t
during
the
summer.
Journal references: Science (DOI: 10.1126/science.1153360,
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