RAPID VARIATIONS IN ATMOSPHERIC METHANE CONCENTRATION DURING THE PAST110,000 YEARS

A methane record from the GISP2 ice core reveals that millennial-scale variations in atmospheric methane concentration characterized much of the past 110,00 years, As previously observed in a shorter record fro m central Greenland, abrupt concentration shifts of about 50 to 300 pa rts per billion by volume were coeval with most of the interstadial wa rming events (better known as Dansgaard-Oeschger events) recorded in t he GISP2 ice core throughout the last glacial period. The magnitude of the rapid concentration shifts varied on a longer time scale in a man ner consistent with variations in Northern Hemisphere summer insolatio n, which suggests that insolation may have modulated the effects of in terstadial climate change on the terrestrial biosphere.