Home > Global warming ’past the point of no return’
Edito International Environment
By Steve Connor, Science Editor
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.
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.