The ice record of greenhouse gases: a view in the context of future changes

Analysis of air trapped in polar ice provides the most direct information o n the natural variability of Greenhouse Trace Gases (GTG). It gives the con text for the dramatic change in their atmospheric concentrations induced by anthropogenic activities over the last 200 yr, leading to present-day leve ls which have been unprecedented over the last 400,000 yr. The GTG ice reco rd also provides insight into the processes generally involved in the inter play between these trace gases and the climate and in particular those whic h are likely to take place in the next centuries in terms of climate change s and climate feedbacks on ecosystems. The paper gives selected examples of the GTG record, taken during different climatic periods in the past, and i llustrating what we can learn in terms of processes. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.