In 1999 he was the lead author of a study published in
Nature, "Climate and atmospheric history of the past 420,000 years from the
Vostok ice core,
Antarctica." The paper presented the first long climate record from the ice. It provided a continuous record of temperature and atmospheric composition. The data extracted from this ice core had implications throughout the fields of
glaciology and
paleoclimatology. One of the concluding remarks was that present day levels of
carbon dioxide and
methane seem to have been unprecedented during the past 420,000 years. The paper has been cited 3953 times to date. == Ice cores ==