Geoscience Reference
In-Depth Information
Melting Sea ice and the
northwest Passage
century. Based on recent rates of sea ice
loss, Muyin Wang and James Overland
project a possible complete loss of summer
sea ice in the Arctic by 2030.
As the ice cover is reduced, the albedo
changes, and the ocean water warms all the
faster. Albedo is the amount of solar radia-
tion reflected by any surface, expressed as
a percentage of the incoming radiation. Sea
ice reflects back 30% to 40% of the incom-
ing radiation it receives from the sun, while
seawater reflects back only 2% to 10% of the
radiation and absorbs the rest. Clouds may
reflect back as much as 90%. The increased
warming of the Arctic Ocean due to the al-
bedo change leads to increased warming on
adjacent lands, adding an additional threat
to permafrost.
One of the exciting ramifications of the
shrinking Arctic sea ice is the possible
opening of the Northwest Passage, a ship-
ping route along the northern tip of North
America that would connect the Atlantic
and Pacific oceans. Transits by submarine
began with the voyage of the uss
Nautilus
,
which traveled under the ice to the North
Pole in 1958 as part of a complete transit
of the Arctic Ocean. In 1959 the submarine
uss
Skate
actually pushed through the ice
at the pole. This passage was long sought
by early explorers including Captain James
Cook from the Atlantic side and Captain Vi-
tus Bering from the Pacific side. A few ships
including an ocean liner and a submarine
(t he uss
Seadragon
) have traversed the pas-
sage in recent years, and if Canadian sov-
The Arctic Ocean is the smallest and shal-
lowest of the Earth's five major ocean ba-
sins. Floating sea ice covers most of it. Typi-
cally there are 15 million square kilometers
(5.8 million square miles) of ice in the Arc-
tic Ocean in the winter, which shrinks to
7 million square kilometers (2.7 million
square miles) in the summer. Most of the
icebergs and ice floes that break of of the
sea ice remain enclosed in the Arctic basin,
but a few escape, as the captain of the
Ti-
tanic
learned.
Since the beginning of satellite records in
1979, the Arctic sea ice cover, which follows
a normal seasonal pattern of melting and
refreezing, has been shrinking at a rate of
about 11% per decade. At the same time, the
average sea ice is getting younger. In 1988
31% of sea ice was five years old or older.
That number dropped to 10% in 2009. The
sea ice cover is also thinning, by 40% over
the last few years. As measured by the aer-
ial extent of the ice in the month of Sep-
tember (considered the time of the mini-
mum “summer” sea ice extent), the years
2007 and 2008 were record minimums
since 1997 (possibly because of particularly
sparse cloud covers). The size of the sum-
mer sea ice cover varies, and in 2009 the
ice cover was more extensive than in 2007
and 2008. Still, current predictions indi-
cate that the Arctic ice cover will be entirely
gone well before the end of the twenty-irst
