Global Warming
'Past
The Point Of No Return'
By Steve Connor
17 September, 2005
The Independent
A
record loss of sea ice in the Arctic this summer has convinced scientists
that the northern hemisphere may have crossed a critical threshold beyond
which the climate may never recover. Scientists fear that the Arctic
has now entered an irreversible phase of warming which will accelerate
the loss of the polar sea ice that has helped to keep the climate stable
for thousands of years.
They believe global
warming is melting Arctic ice so rapidly that the region is beginning
to absorb more heat from the sun, causing the ice to melt still further
and so reinforcing a vicious cycle of melting and heating.
The greatest fear
is that the Arctic has reached a "tipping point" beyond which
nothing can reverse the continual loss of sea ice and with it the massive
land glaciers of Greenland, which will raise sea levels dramatically.
Satellites monitoring
the Arctic have found that the extent of the sea ice this August has
reached its lowest monthly point on record, dipping an unprecedented
18.2 per cent below the long-term average.
Experts believe
that such a loss of Arctic sea ice in summer has not occurred in hundreds
and possibly thousands of years. It is the fourth year in a row that
the sea ice in August has fallen below the monthly downward trend -
a clear sign that melting has accelerated.
Scientists are now
preparing to report a record loss of Arctic sea ice for September, when
the surface area covered by the ice traditionally reaches its minimum
extent at the end of the summer melting period.
Sea ice naturally
melts in summer and reforms in winter but for the first time on record
this annual rebound did not occur last winter when the ice of the Arctic
failed to recover significantly.
Arctic specialists
at the US National Snow and Ice Data Centre at Colorado University,
who have documented the gradual loss of polar sea ice since 1978, believe
that a more dramatic melt began about four years ago.
In September 2002
the sea ice coverage of the Arctic reached its lowest level in recorded
history. Such lows have normally been followed the next year by a rebound
to more normal levels, but this did not occur in the summers of either
2003 or 2004. This summer has been even worse. The surface area covered
by sea ice was at a record monthly minimum for each of the summer months
- June, July and now August.
Scientists analysing
the latest satellite data for September - the traditional minimum extent
for each summer - are preparing to announce a significant shift in the
stability of the Arctic sea ice, the northern hemisphere's major "heat
sink" that moderates climatic extremes.
"The changes
we've seen in the Arctic over the past few decades are nothing short
of remarkable," said Mark Serreze, one of the scientists at the
Snow and Ice Data Centre who monitor Arctic sea ice.
Scientists at the
data centre are bracing themselves for the 2005 annual minimum, which
is expected to be reached in mid-September, when another record loss
is forecast. A major announcement is scheduled for 20 September. "It
looks like we're going to exceed it or be real close one way or the
other. It is probably going to be at least as comparable to September
2002," Dr Serreze said.
"This will
be four Septembers in a row that we've seen a downward trend. The feeling
is we are reaching a tipping point or threshold beyond which sea ice
will not recover."
The extent of the
sea ice in September is the most valuable indicator of its health. This
year's record melt means that more of the long-term ice formed over
many winters - so called multi-year ice - has disappeared than at any
time in recorded history.
Sea ice floats on
the surface of the Arctic Ocean and its neighbouring seas and normally
covers an area of some 7 million square kilometres (2.4 million square
miles) during September - about the size of Australia. However, in September
2002, this dwindled to about 2 million square miles - 16 per cent below
average.
Sea ice data for
August closely mirrors that for September and last month's record low
- 18.2 per cent below the monthly average - strongly suggests that this
September will see the smallest coverage of Arctic sea ice ever recorded.
As more and more
sea ice is lost during the summer, greater expanses of open ocean are
exposed to the sun which increases the rate at which heat is absorbed
in the Arctic region, Dr Serreze said.
Sea ice reflects
up to 80 per cent of sunlight hitting it but this "albedo effect"
is mostly lost when the sea is uncovered. "We've exposed all this
dark ocean to the sun's heat so that the overall heat content increases,"
he explained.
Current computer
models suggest that the Arctic will be entirely ice-free during summer
by the year 2070 but some scientists now believe that even this dire
prediction may be over-optimistic, said Professor Peter Wadhams, an
Arctic ice specialist at Cambridge University.
"When the ice
becomes so thin it breaks up mechanically rather than thermodynamically.
So these predictions may well be on the over-optimistic side,"
he said.
As the sea ice melts,
and more of the sun's energy is absorbed by the exposed ocean, a positive
feedback is created leading to the loss of yet more ice, Professor Wadhams
said.
"If anything
we may be underestimating the dangers. The computer models may not take
into account collaborative positive feedback," he said.
Sea ice keeps a
cap on frigid water, keeping it cold and protecting it from heating
up. Losing the sea ice of the Arctic is likely to have major repercussions
for the climate, he said. "There could be dramatic changes to the
climate of the northern region due to the creation of a vast expanse
of open water where there was once effectively land," Professor
Wadhams said. "You're essentially changing land into ocean and
the creation of a huge area of open ocean where there was once land
will have a very big impact on other climate parameters," he said.
© 2005 Independent
News & Media (UK) Ltd.