For the last 800 thousand years we have a precise record of atmosphere CO2 content. It is based on the analysis of air trapped in small bubbles in Antarctic ice. During the sintering process which converts snow into ice, air is trapped in small bubbles which occupy about 10 percent of the volume. The trapped air is pristine. It preserves the original composition including that for the trace gases CO2 and CH4.

As shown in Figure 6.1, this CO2 record is similar to that for Antarctic air temperature. This led Al Gore, in his...

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