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The main features of the more recent Vostok climate cycle have similarities with those seen in earlier cycles. It has been possible to identify a strong connection between atmospheric greenhouse-gas concentrations and Antarctic temperature, along with the strong imprint of obliquity and precession in most of the climate time series. This research supports the view that greenhouse gases have played a strong role in the glacial-interglacial change.

A new glaciological time-scale that is consistent with ocean records has been established for the Vostok station in Antarctica. Ice-core records which reveal local temperature, dust accumulation and air composition extend the glaciological time-scale to the penultimate glacial period, approximately 140,000 to 200,000 years ago. Vostok's penultimate glacial period was colder t the most recent one, and concentrations of carbon dioxide and CH4 correlate well in relation to temperature throughout the record.

Gases trapped in polar ice provide our most direct record of the changes in greenhouse gas levels during the past 150,000 years. The best documented trace-gas records are for [CO.sub.2] and [CH.sub.4]. The measurements corresponding to the industrial period document the recent changes in growth rate. The variability observed over the last 1000 years constrains the possible feedbacks of a climate change on the trace gases under similar conditions as exist today. Changes in the levels of greenhouse gases during the glacial-interglacial cycle overall paralleled, at least at high southern latitudes, changes in temperature; this relation suggests that greenhouse gases play an important role as an amplifier of the initial orbital forcing of Earth's climate and also helps to assess the feedbacks on the biogeochemical cycles in a climate system in which the components are changing at different rates., Man has caused large increases in atmospheric concentrations of [CO.sub.2], [CH.sub.4], and [N.sub.2]O since 1800, and of chlorofluorocarbons (CFCs) since 1950. We urgently need to understand how sensitive Earth's climate [...]

Palaeoclimatologists are likely to obtain significant new information from studying the Russian Vostok ice core, which is now thought to cover the past four glacial-interglacial cycles. International research already undertaken indicates that the ice layers thin linearly with depth below 2,755 mt. At 3,139 mt depth, the ice is 340,000 years old. It will soon be possible to obtain a wide range of climate information which is up to around 400,000 years old.

D. Raynaud et al. (1) describe the processes affecting the composition of trapped air in polar ice. They state (1, p. 927) It was recently shown that the composition of [...]