15/06/2004

A study published in the latest issue of the journal Nature details how the deepest ice cores yet drilled are helping climate scientists paint a clearer picture of previous climatic changes. Chemical analysis of the cores, which are nearly two miles long, is helping scientists better understand the eight previous ice ages that have occurred in the last 740, 000 years.

By analysing the microscopic bubbles of air that were trapped in the East Antarctic ice sheet when it formed, scientists can measure the levels of carbon dioxide and other green house gases that were present in the atmosphere at the time. They can also use the ice cores to estimate the global temperatures at the time they were formed.

What the international team of scientists working on the cores have found provides further proof, if any now were needed, that human activities are destabilising the global climate. They have found that present climate resembles, most closely, the warm “interglacial period” of 470,000 years ago, which lasted 28, 000 years. At this time the Earth had a very similar orbit around the sun to the one it does today, making the climate , then and now very similar. However, instead of us being able to expect a further 15,000 years of relative stability, as analysis of the cores would suggest, temperatures, are now spiralling upwards as a result of 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 wrote.

This has significant implications for the debate about global warming, because some people have speculated that global warming is to be welcomed as it could avert the next ice age. We now know that while some interglacial periods have only lasted 6, 000 years, prompting such speculation, the one that most closely resembled our own interglacial period lasted 28,000 years. Eric Wolff, a senior member of the team from the British Antarctic survey in Cambridge put it this way:

“If the climate is left to it’s 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.”

Levels of CO2

The ice cores retrieved from the East Antarctic ice sheet have doubled the length of the record of greenhouse gases in the atmosphere. Previous Ice cores only went down as far as 400, 000 years. It is now possible to see a record of greenhouse gas concentrations that stretches back over seven hundred thousand years, giving scientists an even better yardstick by which to judge whether the currently high levels of CO2 in the atmosphere are unusual.

The records for similar interglacial periods during the last half a million years show that the typical level of CO2 in the atmosphere has been around 280 parts per million. Today the concentrations of CO2 in the atmosphere stand at 375 parts per million.

Human activities, it seems, have forfeited a period of climatic stability by releasing billions of tons of heat trapping gases into the atmosphere over the last 150 years. This has left us with concentrations of CO2 that exceed by 30%, the levels we have seen at any time during the last 400, 000 years. As the report in Nature concluded, the Earth’s climate would now be in a highly stable period if not for the this extra CO2 being emitted into the atmosphere by humans.

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