Ice cores from Greenland and Antarctica indicate significant and rapid changes in atmospheric methane concentrations (CH4) that are associated with climate change.

A rapid increase of [CH4] took place during the abrupt change in climatic conditions during the transition Dryas lower-Préboréal (about 11,600 years ago). The possible sources of methane are the wetlands, the marine clathrates and the lakes of thermokarst. The possibility that the tanks of clathrates become unstable in response to the climate change is particularly worrying because if only 10% of methane clathrate reservoir of non-fossil was released into the atmosphere, its forcing radiative would be equivalent to an increase in approximately 10 times of atmospheric carbon dioxide.

To establish the source of methane, the concentration of carbon 14 (14C) of methane (14CH4) were measured in Greenland ice formed in the transition climate. The atmospheric carbon dioxide is the main source of carbon for the production of methane in wetlands, 14CH4 should either not change or increase after an abrupt global warming. On the other hand 14CH4 should decrease if the clathrates constituted the only source of methane because, being geologically old, they contain only little or no 14C.

The results of the study by an international team of Australian scientists with the Australian Nuclear Science and Technology Organization (ANSTO) and CSIRO show 14CH4 values higher than predicted paleoatmospheric values. In situ production of cosmogenic 14CH4 molecules in ice could explain these high values. Carbon monoxide CO and 14C were measured to correct the values of 14CH4. The corrected values suggest that the methane was released by the wetlands at the end of the last glacial period.