Atmospheric carbon dioxide and methane concentrations in the past and synchronisation of ice core records from both hemispheres based on methane results

In the central parts of the large polar ice sheets ice is formed by dry sintering of cold snow. The analyses of air extracted from bubbles of well dated ice samples from such locations, allow to determine the composition of the atmosphere at the time of ice formation. Of special interest are the two dominant greenhouse gases carbon dioxide and methane. The methane concentrations are very reproducible and represent the atmospheric concentration at the time of ice formation with a good accuracy. The records show unexpected variations of this concentration during the glacial epoch as well as during the Holocene. The concentration differences measured on ice cores from Greenland and Antarctica allow to determine concentration differences between the Northern and Southern Hemispheres. Ice core records show that the atmospheric CO_2 concentration has increased steadily from about 280 ppmv in 1750 to the present value of about 355 ppmv and that the large climatic change from the last glacial to the post glacial epoch was accompanied by a naturally caused increase of the atmospheric CO_2 concentration from about 200 ppmv to 280 ppmv. However, uncertainties about a possible CO_2 production in the ice make the investigation of smaller variations and accurate time lags between climatic changes and changes of the atmospheric CO_2 concentration especially in Greenland ice cores difficult. A synchronisation of ice core records from Greenland and Antarctica by methane results allows to compare CO_2 records from Antarctica with climatic records from Greenland