Fig. 3.

Enhanced chemistry-climate feedbacks in past greenhouse worlds. Simulated equilibrium surface temperature increases (ΔT) by elevated trace greenhouse gas concentrations (Table 1) on the 4 × CO₂ Eocene (A, B) and 4 × CO₂ Cretaceous (C, D) during northern hemisphere winter (DJF) and northern hemisphere summer [June July August (JJA)] climates respectively. Feedbacks were quantified with the coupled ocean-atmosphere GCM HadCM3L by prescribing PI and elevated levels of trace GHGs (Table 1). Only temperature differences exceeding 95% confidence limits are displayed. (E) and (F) indicate the relative contribution of each greenhouse gas to land surface mean annual temperature increases in the Eocene and Cretaceous respectively.