Studies reported that the Arctic sea ice extent had shrunk by 7.4 per
cent over the past 25 years, with record-low coverage in September 2002
(Johannessen and others 2003). An analysis of 30 years of satellite
data suggests that the loss of Arctic sea ice is also accelerating (Cavalieri
and others 2003).
There are projections that much of the sea ice, until now thought to
be permanent, will melt during the summer by the end of this century
if the current trend in global warming continues. This will have major
direct impacts on indigenous people and Arctic marine wildlife such
as polar bears and seals, and will also open the region to increased
development pressure as access by sea to valuable natural resources
becomes easier (Figure 1). The global impacts may also be significant
as absorption of solar radiation increases, and could lead to changes
in the world ocean circulation (UCL 2003, NASA 2003, Laxon and others
|Figure 1: Projection of Arctic sea ice extent by
2030 and possible ice-free transpolar shipping routes
Source: New Scientist 2002
In the Antarctic, satellite data indicate that the overall extent
of sea ice has gradually increased since 1977, following a significant
decrease in the early part of the 1970s (Cavalieri and others 2003).
This reversal demonstrates a greater variability in the trend for
Antarctic sea ice extent in comparison to a more consistent trend
of decline in the Arctic.
However, on the Antarctic peninsula, and in the Amundsen Sea sector
of west Antarctica, several ice shelves that were thousands of years
old have disintegrated within the last few decades – a sign
of rapid change in the region (Shepard and others 2003).
Argentine scientists have documented surges in tributary glaciers
following these break-ups (de Angelia and Skvarca 2003). Their study
– with new results from theoretical models – suggests
that ice shelves may play an important role in the stability of some
inland ice streams, and their loss could result in the accelerated
collapse of glaciers.
Particular attention is being paid to the behaviour of critical ice
flows in the West Antarctic ice sheet, which could raise global sea
level by five metres, were it to collapse completely (Casassa 2003).
The break-up of the Ward Hunt sea ice-shelf in northern Canada (Box
1), the Arctic’s largest, was also reported in 2003 (Mueller and
others 2003). The Ward Hunt has existed for some 3 000 years. When it
was mapped by explorers in the 1870s it was 1 000 km long and 60 km
wide. By the late 1990s, its dimensions had decreased to some 70 km
by 20 km, and now it’s disintegration is almost complete.
This sequence may be attributed to natural climate variability. However,
just as the recent collapse of ice shelves in west Antarctica has been
interpreted as evidence of accelerated climate change in that region,
the break-up of the Ward Hunt may suggest the same in the high Arctic
(Mueller and others 2003).
Box 1: Ward Hunt
Source: NASA and Earth Observatory
The Arctic’s largest ice-shelf is breaking
up. The Ward Hunt Ice-shelf is a remnant of the compacted
snow and ancient sea ice that extended along the northern
shores of Ellesmere Island in Northern Canada until the early
20th century. Rising temperatures have reduced the original
shelf into a number of smaller shelves, the largest of which
was the Ward Hunt Ice-shelf on the northwest fringe of the
island. Between 2000–2002, the Ward Hunt Ice-shelf began
to crack and eventually broke in two. This Standard Beam Mode
RADARSAT-1 image, which was acquired September 27, 2003, clearly
shows a large crack dividing the ice-shelf in half. The crack
runs from the Arctic Sea to the right of Ward Hunt Island
and the bright white ice grounded there and back to the rougher,
|Source: Earth Observatory 2003
Break-up of the Ward Hunt Ice-shelf.