Early Eocene Arctic climate sensitivity to pCO2 and basin geography

We present results from new early Eocene (∼55–45 Ma) climate modeling experiments with the NCAR Community Climate System Model. These experiments test the sensitivity of climate to a large increase in atmospheric greenhouse gases, such as may have occurred at the Paleocene‐Eocene (P‐E) boundary (∼55.5 Ma), and also allow us to explore the role of Arctic basin configuration on climate. Experiments were run with pCO 2 at 560 and 2240 ppm, and a third experiment, at 2240 ppm, incorporates a passage to a neighboring ocean to explore the potential effect of the ocean on Arctic warming, were the Arctic not isolated. Quadrupling pCO 2 warms the Arctic by ∼8°C in the annual average, doubles atmospheric moisture content in this region and eliminates Arctic sea ice, consistent with proxy estimates of warming at the P‐E boundary. Opening the Arctic Ocean warms mean annual sea surface temperature by an additional ∼4°C.