The break-up of the Larsen
B ice shelf in early 2002. This event has been attributed
to the effects of global warming. That it occurred is beyond
dispute and that it is a result of the warming of the Antarctic
Peninsula where it is situated is also beyond dispute. What
remains unclear is whether or not this is a taste of things
to come and an indicator of an Antarctic-wide phenomena
or simply a localized result of the localized warming of
the Antarctic Peninsula region alone.
An ice shelf is a thick layer
of ice that is floating on the sea. They are fed from the
land by glaciers. Where the ice leaves the land and starts
to float on the sea is a region known as the "hinge zone"
where the ice is particularly chaotic, broken-up and a nightmare
to try and travel over. Ice shelves surround much of Antarctica.
The Larsen B ice shelf was
about 220m thick (720 feet) and during a 35 day period in
early 2002 lost about 3,250 km2 of ice into the
ocean. It is thought to have been in existence for at least
400 years prior to this and probably as long as 12,000 years
since the end of the last ice age.
Such a disintegration in
such a short time period is therefore an extremely significant
event. What now remains of the Larsen B is about 40% of
what was there in 1995. It had been breaking up at what
was considered to be a rapid rate anyway before this major
event. The break-up is thought to be a consequence of higher
temperatures and large amounts of summer melt-water running
down crevasses in the ice shelf so speeding the disintegration
Overall in the Antarctic
Peninsula, seven ice shelves have between them declined
in area by about 13,500 km2 since 1974.
A more recently seen phenomena
that follows this ice shelf collapse is that the glaciers
that fed the ice shelf seem to now be speeding up their
flow down to the sea. This will certainly deposit more
water in the oceans, and as this was previously on the land
it will add to an increase in sea-level. The Antarctic peninsula
doesn't have enough ice to make much of a difference to
sea level in itself even if it were all to melt, but it
is best seen as an indicator region that can be observed
to enhance understandings of the mechanisms in other parts
of the world.
Prince Gustav Channel
Evidence from seabed sediments
in the Prince Gustav Channel on the Antarctic Peninsula
after the ice shelf that previously blocked it collapsed
has shown that it had disappeared at least once before in
the last 10,000 years.
"Thus, the present loss
of ice shelves cannot be assumed to be a consequence of
Man-made climate change, unless and until a cause can be
British Antarctic Survey
The Prince Gustav Channel in 1985
A photograph that may not
be able to be taken again for a few hundreds or even thousands
of years. In 1985, HMS Endurance is moored up to the
ice barrier that blocked the Prince Gustav channel between
James Ross Island and the Antarctic Peninsula. Standing
by the ship and looking to the left in the picture, the
ice slope could be seen to rise to well over 100 feet (30m)
altitude into the distance (and 9 to 10 times that thickness
under the level of the sea). Today, the whole lot has gone.
West Antarctic Ice
The West Antarctic Ice Sheet
(to the west of the Antarctic Peninsula) has thinned significantly
as a result of warmer temperatures in the surrounding Antarctic
Ocean. The upper ocean in this region has increased in temperature
by more than 1°C since 1955. The greatest degree of thinning
has happened in an area called the Amundsen Sea Embayment.
Many glaciers have retreated
and 10 ice shelves have been seen to retreat in recent years.
87% of glaciers along the west coast of the Antarctic Peninsula
have retreated in the last 50 years with most of these showing
accelerated retreat in the last 12 years.
Antarctica has ice that is up to
4700m thick. This ice preserves a record of the conditions
at the time it was frozen, of the amounts of gases in the
atmosphere and an indication of the temperature. The deeper
you drill, the further back in time you go.
ice cores show that current atmospheric carbon dioxide and
methane gas levels (both greenhouse gases) are higher than
at any time in the last 800,000 years. The rate of increase
of these gases is faster than any likely to have happened
in the recent geological past. This 800,000 year record
came from a 3km long ice core.