The now iconic 800,000-year Antarctic ice core records that show how climate and greenhouse gases vary on long-term ice age cycles are now complemented by new data that include: 1) snapshot views of much older time periods from Antarctic ice sheet margins, 2) very high resolution data that reveal the dynamics of abrupt changes in biogeochemical cycles during ice ages and interglacial periods and, 3) increasingly accurate and detailed measurements of isotopic ratios and new trace species that resolve long standing questions and raise new ones.
This talk will summarize recent results that provide new views of the links between climate and greenhouse gases on both long and short time scales, focusing primarily on the cycles of atmospheric methane and carbon dioxide. In the ice core record methane is dominated by abrupt variations during ice ages that are now recorded in exquisite detail. New isotopic and other data increasingly point to tropical processes as responsible for much of the variability, and call in to question the importance of fossil sources for abrupt changes. We also now recognize very abrupt changes in atmospheric carbon dioxide and are exploring the mechanisms that might be responsible. On longer time scales new data from Antarctic ice cores allow precise evaluation of the timing of Antarctic temperature and carbon dioxide change at the end of the last ice age, and show they are very tightly coupled, to the extent that leads and lags are not really discernable. On even longer time scales preliminary results from very old ice (1-2 Myr and slightly older) do not suggest very large differences in greenhouse gases relative to later times, but seem to imply that methane maxima were lower and carbon dioxide minima were higher. The implications of these findings are just now being explored.