Ice core reveals a worrying truth about Earth's climate

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Ice core reveals a worrying truth about Earth's climate
http://news.independent.co.uk/world/science_technology/story.jsp?story=52991
5
Scientists drilling in the Antarctic have found evidence that man-made
greenhouse gases are causing the planet's climate to destabilise - and could
bring on a new ice age in 15,000 years. Steve Connor reports
10 June 2004
The deepest and oldest ice core yet drilled in the Antarctic suggests that
the world's climate is headed for an unprecedented period of turmoil brought
about by man-made greenhouse gases.
Chemical analysis of the ice within the core - nearly 2 miles long - has
revealed details of the eight previous ice ages that have affected the Earth
durin the past 740,000 years. Scientists say that the present climate most
closely resembled the warm "interglacial" period about 470,000 years ago,
but with the difference that this time temperatures were set to spiral
upwards as a result of global warming.
In a study published today in the journal Nature, the international team of
scientists from 10 European countries warns that the Earth's climate would
now be in a highly stable period if it were not for the extra carbon dioxide
being pumped into the atmosphere from human activities. "Given the
similarities between this earlier warm period and today, our results may
imply that without human intervention, a climate similar to the present one
would extend well into the future," the scientists say.
Eric Wolff, a senior member of the team from the British Antarctic Survey in
Cambridge, said that anyone who suggested human-induced global warming was
beneficial because it would avert the next ice age was misguided. "If the
climate is left to its own devices, we have about another 15,000 years to go
before the next ice age. If people say global warming is good because it
stops us going into another ice age, they are wrong because we are not about
to go into another ice age," Dr Wolff said.
The deepest ice cores were drilled at a site known as Dome C, where the East
Antarctic ice sheet is about 3.4km (2 miles) thick. It is one of two sites
being drilled on the frozen continent as part of the European Project for
Ice Coring in Antarctica (Epica), which began field work in 1996.
Tiny bubbles of air were trapped in the ice when it formed from snow falling
on the Antarctic ice sheet. That ancient air is being analysed to see how
much carbon dioxide and other greenhouse gases such as methane were present
in the atmosphere over many hundreds of thousands of years.
The ice cores retrieved from the Epica study will double the length of the
record of greenhouse gases in the atmosphere, making it possible to judge
just how unusual are today's high concentrations of carbon dioxide - the
principal greenhouse gas behind global warming. "We've never seen greenhouse
gas concentrations anything like as high as that we're seeing today," Dr
Wolff said.
Levels of methane, another greenhouse gas, were about two and a half times
as high as historic levels, said Thomas Stocker of the University of Bern in
Switzerland, another senior member of the team.
Dr Stocker said concentrations of carbon dioxide in the air today stood at
about 375 parts per million (ppm), whereas the typical level for a similar
interglacial period over the past half million years was about 280ppm.
"Today, we have levels of carbon dioxide that exceed by 30 per cent the
levels that we have ever had over the past 400,000 years," Dr Stocker said.
Professor James White of the University of Colorado at Boulder, said that
the ice core retrieved from Dome C was telling scientists not just about
greenhouse gases from the past, but also helping them to estimate global
temperatures at the time the ice formed and how these were linked with
changes in the composition of the atmosphere. "This has the potential to
separate the human-caused impacts from the natural and place them in a much
clearer context," Professor White said. "We're living in an unusual time. In
the past 430,000 years, the percentage of time the climate was as warm as it
is today is quite small, about 5 to 10 per cent, and before that, it appears
to never have been that warm."
The data from the ice cores show that, typically, the warm period between
two ice ages lasted about 6,000 years, but the current warm period since the
last ice age had already lasted 12,000 years, Professor White said. That has
led some commentators to speculate that we are about to be plunged into
another ice age, with the suggestion that global warming is to be welcomed.
"Humans have been active in messing with the carbon cycle for a long period
of time. Here, we are warming the planet, while at the same time,
climatologists will tell us that we are perhaps long overdue for a glacial
period," Professor White said. However, the interglacial period of four ice
ages ago lasted much longer, about 28,000 years. That was also the time most
like the interglacial period that we were now experiencing, the scientists
said.
"One of our biggest scientific questions is: is glaciation overdue? For our
future it is very important that we understand how these huge glaciers
start," Professor White said.
The ice sheet of Dome C is one of the most inhospitable places on Earth with
average surface temperatures of minus 54C. At an altitude of 3,233m above
sea level, the ice station at Dome C is so cold and dark for much of the
year that the scientists can only carry out drilling for two out of every 12
months.
The second Epica drilling station is at Dronning Maud Land, which is at a
slightly lower altitude of 2,892m above sea level, where average surface
temperatures are a relatively balmy minus 44C. About 300km north of dome C
is a third, much older, drilling site called Vostok, which was established
by Russian scientists 40 years ago. That is the place where the previous
oldest and deepest Antarctic ice core was retrieved, descending about
400,000 years.
Unfortunately for the scientists the Vostok ice core finishes just at the
very moment in history when the Earth appears to have been in a very similar
orbit around the Sun to the orbit to that it is on currently, making the
climate, then and now, very, similar. The limitation arose because the
Vostok site is above an ice-covered lake, making it impossible to drill any
deeper.
Epica scientists decided, therefore, to explore the much thicker ice sheet
covering Dome C, which is on solid bedrock. The scientists believe that the
hole drilled into the ice sheet of Dome C is now only about 100m above the
ground, which has been covered in ice for so long that it has not been
exposed to the atmosphere for at least 1 million years.
Chemical analysis of the water and the trapped bubbles of air in the Dome C
ice core has revealed something of the nature of the eight previous ice ages
and warm interglacial periods that have dominated life on Earth over the
past 800,000 years.
The core shows clearly, for instance, that during the past half a million
years the Earth has settled into a period where there are glacial cycles
lasting about 100,000 years which match, to some extent, the cyclical nature
of the planet's elliptical orbit around the Sun.
In the half million years before about 450,000 years ago, the extremes
between the middle of an ice age and the middle of an interglacial period
were less pronounced and the cycles were shorter, lasting about 40,000
years.
Scientists do not know how to explain the difference between the two
periods. One possibility is that the world's ice sheets and glaciers have
grown progressively bigger, making it more difficult for the ice to respond
to a planetary shorter cycle.
Life for the 50 scientists trying to answer those questions at Dome C can be
bleak and isolated, although conditions are made as comfortable as possible
with a sauna and unrestricted access to hot showers. Much of the physically
strenuous work is focused on the mechanics of getting the core to the
surface. The ice is collected in a metal tube 3.5m long and 10 cm wide,
which is attached to a mechanical drill bit.
Each stage of the drilling brings its own problems. Ice extracted from the
first 1,000m, for example, is so brittle that the sudden release of pressure
can cause it to shatter with an explosive force. In 1998, the drill became
irretrievably stuck in its hole when chips of ice formed by the grinding
process froze solid around the bit. The scientists then had to begin a fresh
hole at a nearby site.
This time, they reduced the length of the ice core pulled up to the surface
to less than 3m. It is a time-consuming process, given that it can take up
to an hour to bring a sample to the surface from a hole more than 3km deep.
This December - at the height of the Antarctic summer - drilling will resume
at Dome C when the scientists hope to complete a core dating back more than
900,000 years.
The final 100m before they reach solid bedrock poses one of the most
difficult technical problems because, at its extreme depth, The ice is near
to melting point due to the geothermal heat coming from the ground, which
can quickly refreeze around the drill, causing it to seize up.
No doubt the scientists will celebrate when the finally reach rock bottom of
the deepest ice hole in the world. Dominique Raynaud of the French national
research centre said: "None of us knows what we'll find at the bottom of
Dome C: that's why it's exciting."