Tipping Point 9.16.2005

Global Warming May Be "Past the Point of No Return"

Steve Connor of The Independent, UK

Recent scientific observations suggest that global warming may have passed a critical tipping point, a point of no reutrn.

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 U.S. National Snow and Ice Data Center 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 Center who monitor Arctic sea ice.

Scientists at the Data Center 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
neighboring 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.

Source

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