Close coupling of climate with green house gases in the past

Never before during the past 650,000 years, have concentrations of green house gases been as high as today. The warm climate periods between 650,000 and 420,000 years ago were characterised by even lower carbon dioxide and methane concentrations than subsequent warm periods. This is one of the conclusions drawn by a European team of researchers with contribution from scientists of the Alfred Wegener Institute for Polar and Marine Research, after analysis of an ice core from Antarctica. The results extend previous data on historic concentrations of carbon dioxide, methane and nitrous oxide in the atmosphere by 250,000 years.

In two studies published in the scientific journal Science, researchers from the University of Bern, together with their colleagues from France and Germany, demonstrate that, over the past 650,000 years, low green house gas concentrations have been associated also with cooler conditions. “The link between temperature and carbon dioxide, as well as methane concentrations in the past is surprisingly constant over time. Only through the impact of humans during the last centuries, atmospheric green house gases have been raised above their natural levels”, explains Dr Hubertus Fischer of the Alfred Wegener Institute. Prof Dr Thomas Stocker of the Physics Institute at the University of Bern in Switzerland adds: “The analysis highlights the fact that the current concentration of atmospheric carbon dioxide, 0.38 volume parts per thousand, already exceeds the highest level recorded over the past 650,000 years by 27 percent.”

As part of the European Project for Ice Coring in Antarctica (EPICA), the ice core was retrieved from the Antarctic plateau at Dome C. Ultimately, ice cores date back to individual snowfalls which, over time, have been transformed into glacial ice. Approximately ten percent of teh volume of an ice core consists of air bubbles trapped among the ice crystals. By analysing the trapped air, as well as the chemical composition and the physical properties of the ice, scientists are able to draw conclusions about atmospheric processes and climate changes in the past.

The drilling at Dome C was completed in the past winter. Hence, even older ice is available for further measurements. The glaciologists estimate that the ice cores not yet analysed contain undisturbed climatic history dating back approximately 900,000 years. The EPICA project is carried out by a consortium of ten European countries (Belgium, Denmark, Germany, Great Britain, France, Italy, the Netherlands, Norway, Sweden and Switzerland). EPICA is coordinated under the umbrella of the European Science Foundation (ESF) and funded by the participating countries and the European Union. EPICA’s goal is to obtain two ice cores, extending all the way to the underlying bedrock, from the Antarctic inland ice. Apart from drilling at Dome C (75° 06’S, 123° 21’E), a second core, currently at a depth of 2565 metres, is being taken at Kohnen Station in Dronning Maud Land (75°00'S, 00°04'E).

The Alfred Wegener Institute is the German EPICA partner and carries responsibility for the coring in Dronning Maud Land. Presently, the European researchers are, once again, in the Antarctic to complete drilling this season and reach the bedrock. The project EPICA represents one of the central projects within the research concept ‘Ocean, Coastal and Polar Systems’, part of the research field ‘Earth and Environment’ at the Helmholtz Association. Dr Hubertus Fischer directs a team of young researchers at the Alfred Wegener Institute. He coordinates working groups investigating the air trapped in ice cores.

The articles “Stable Carbon Cycle-Climate Relationship During the Late Pleistocene” and “Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores” will be published November 25 in “Science” (vol. 310, issue 5752).

Your contact person is: Dr. Hubertus Fischer (0471-4831 1174).

Bremerhaven, November 24, 2005.

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