Nye forskningsresultater bekrefter den kraftige uttynningen av havisen i
Arktis. Tykkelsen er halvert på 20 år.
Karsten Johansen
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1058000/1058353.stm
Thursday, 7 December, 2000, 11:36 GMT
Arctic sea ice 'thins by almost half'
The North Pole's ice has begun to disappear
By environment correspondent
Alex Kirby
Two UK scientists say they have found evidence to show that sea ice is
thinning across the Arctic.
The two, Dr Peter Wadhams and Dr Norman Davis, are from the Scott Polar
Research Institute in Cambridge.
They say their work shows that the ice in the Fram Strait, between Svalbard
and Greenland, thinned by nearly half in two decades.
And they say the findings have serious implications for climates at high
latitudes.
Compatible
Dr Wadhams told BBC News Online: "Between summer 1976 and summer 1996 there
was a 43% thinning of sea ice over a large area of the Arctic Ocean between
Fram Strait and the North Pole.
"This came out of measurements which I did (on both occasions) from British
submarines - Sovereign in 1976 and Trafalgar in 1996.
"We covered the same regions of the Arctic and used the same equipment, so
the results are fully compatible.
"The amount of thinning, which is very large, agrees with results published
last year by Drew Rothrock, of the University of Washington, for thinning
rates on the other side of the Arctic.
"That region, from the North Pole to the Bering Strait, was measured by US
submarines over approximately the same interval.
"So this confirms that the thinning of sea ice is an Arctic-wide effect."
Dr Wadhams and Dr Davis report their work in Geophysical Research Letters,
published by the American Geophysical Union.
The data on ice thinning were collected by two upward-looking sonar systems
mounted on the submarines.
The thinning of the ice between Fram Strait and the Pole was first reported
by Dr Wadhams in 1990.
He had found a 15% decrease in ice thickness between his voyage in 1976 on
Sovereign and another in 1987 on a third UK submarine, Superb.
Disputed cause
The authors write: "We note that this loss of ice thickness, although at the
time it appeared large, was actually an underestimate of the thinning which
must have taken place between 1976 and 1987."
This, they say, was because the 1987 experiment was conducted at a different
time of year and using a different sort of sonar.
They add: "Comparing our present results with those reported in 1990, we
speculate that a substantial part of the thinning that occurred in the
experimental region between 1976 and 1996 took place during the first of
those two decades."
Many scientists are convinced that human influences are responsible for the
thinning of the Arctic sea ice, though not all.
Some point to the influence of a natural climate phenomenon known as the
Arctic Oscillation (AO).
Implications
This is an erratic see-saw that alternately raises and lowers atmospheric
pressure over the North Pole while lowering and raising it in a ring around
the polar region.
Dr Wadhams and Dr Davis end their report on a cautionary note. They write of
"the very rapid changes which are occurring in the ocean structure of the
Arctic, with a greater influx of heat into the Atlantic layer".
And they say: "We feel that this additional support for the dramatic
thinning rates reported by Drew Rothrock and others has serious implications
for the future of high-latitude climates."
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