This week's Science Magazine has papers on earth's greenhouse gases as studied from air bubbles in a 750,000 year ice core drilled in Antarctica. Only the summaries are available at the online Science, and it there doesn't seem to be full-text in the magazine databases either. The printed 11/25/05 issue hasn't arrived yet but when it does it will be in the magazine room at Main.
Meanwhile you can extract the gist of their findings from news stories: Christian Science Monitor ; Los Angeles Times ; New Scientist. Or try Richard Alley's The two-mile time machine : ice cores, abrupt climate change, and our future (2000). Alley was one of the scientists working on the Greenland ice core project in the 1990s, and describes just how this kind of work is done.