The Temporal Relationship of Temperature and CO2 Over the Past 40 Million Years
Climate and atmospheric CO2 history for the past 40 million years (Ma). Benthic δ18O from Zachos et al. (2008). Major warming (red arrows) and cooling (blue arrows) events are labelled. Purple bars indicate brief history of Antarctic and Northern Hemisphere ice sheets. Antarctic glaciation thresholds (approx. 750 ppm) and Northern Hemisphere glaciation threshold (approx. 280 ppm) deduced from climate models (DeConto et al., 2008) are marked by dashed lines.
Figure and caption from Figure 5 in Zhang et al. (2013).