Ice Core Reveals a Worrying Truth about Earth's Climate ; 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

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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 said yesterday 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. …