Title: Global warming 'past the point of no return'
Source: Copyright 2005, Independent
Date: September 16, 2005
Byline: Steve Connor

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.