Simulating the mid-Pliocene warm period with the CCSM4 model

We simulate the mPWP using the "alternate" protocol prescribed by the Pliocene Model Intercomparison Project (PlioMIP) for the AOGCM simulation (Experiment 2). Results from the CCSM4 mPWP simulation show a 1.9 °C increase in global mean annual temperature compared to the 1850 preindustrial control, with a polar amplification of ~3 times the global warming.

Global precipitation increases slightly by 0.09 mm day-1 and the monsoon rainfall is enhanced, particularly in the Northern Hemisphere (NH). Areal sea ice extent decreases in both hemispheres but persists through the summers. The model simulates a relaxation of the zonal sea surface temperature (SST) gradient in the tropical Pacific, with the El Niño-Southern Oscillation (Niño3.4) ~20% weaker than the preindustrial and exhibiting extended periods of quiescence of up to 150 yr.