[Peace-discuss] Worth a read.

[Chuck Minne]

Global Warming 'Past the Point of No Return'

by 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.

© 2005 Independent News & Media (UK) Ltd. 



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