|
Drillings carried out in the Antarctic ice at the Russian base of Vostok, close to the South Pole, have allowed core samples of ice from depths of several thousand metres(3 650 m) to be brought up to the surface. Analysis of air bubbles trapped inside these cores has enabled the study of climatic variations over the last 650 000 years. A direct relationship has been established between the temperature ruling at the surface of the planet and the levels of carbon dioxide (CO2) and methane (CH4) in the atmosphere: there is a correlation between increases in temperature and increases in the concentration of these two greenhouse gases.
Each « warm » period, every 100 000 years or so, corresponds to an increase in the CO2 and CH4 content of the atmosphere, and each « cold» period to a decrease in the same figures. However, the warmest period observed in this study corresponds to a CO2 content of approx. 300 ppm (parts per million), attained after a short geological period of some 10 000 years. The level of carbon dioxide today is 380 ppm (i.e. 27 % higher) and it is just 200 years of human activity that have caused this peak. |