Global warming 'past the point of no return'

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http://news.independent.co.uk/world/science_technology/article312997.ece

 

 

 

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16 September 2005 06:34

 

Global warming 'past the point of no return'

 

By Steve Connor, Science Editor

Published: 16 September 2005

 

 

 

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