FIG. 25.9 Atmospheric CO₂ content for the past 400,000 years. These measurements were recorded from air bubbles trapped in glacial ice at Vostok, Antarctica. Source: Data from P. Rekacewicz, “Temperature and CO₂ Concentration in the Atmosphere over the Past 400,000 Years,” from Vital Climate Graphics, UNEP/GRID–Arendal MAPs & Graphics Library, JPG file, 2005, http://www.grida.no/publications/vg/climate/page/3057.aspx. Based on J. R. Petit et al., 1999, “Climate and Atmospheric History of the Past 420,000 Years from the Vostok Ice Core, Antarctica,” Nature 399:429–436.