from PART I - Climate change mitigation: scientific, political and international and trade law perspectives
Published online by Cambridge University Press: 04 August 2010
Greenhouse gas concentrations in the long-term perspective
As part of the European Project for Ice Coring in Antarctica (EPICA), an ice core of 3,270 metres in length was drilled at Dome Concordia (75° 06′ S, 123° 21′ E, 3233 m.a.s.l., −54.5°C mean annual temperature, 2.5 cm H2O precipitation per year). This ice contains information on climate evolution over the last 800,000 years. Important results of the analysis of the ice and the enclosed gas are now available and provide a unique context within which the present changes in the climate system should be interpreted.
The top layers of a polar ice sheet consist of firn (compacted snow), which is in contact with the atmosphere above. Air is exchanged with the atmosphere and can circulate freely in channels of the porous firn. Beyond a depth of about 80 metres, the high pressure of the overlying ice constricts the channels progressively until air bubbles are formed. Analysis of the air enclosed in these bubbles permits the reconstruction of past concentrations of the most important greenhouse gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Measurements demonstrate that the current concentration of CO2 is higher by 27 per cent, and that of CH4 by 130 per cent, than any concentration during the last 650,000 years before industrialisation. Many different and independent studies show that these increases are caused primarily by the burning of fossil fuels, the change of land use and the production of cement.
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