DATA/MODEL COMPARISON FOR THE MID-PLIOCENE WARM PERIOD: THE NASA/GISS MODELE2-R CONTRIBUTIONS TO THE PLIOCENE MODEL INTERCOMPARISON PROJECT, PHASE 1

The climate of the mid-Pliocene Warm Period (mPWP) is of great interest for its similarities to aspects of future climate projections (e.g., IPCC AR4, 2007), especially with regard to marine and terrestrial paleoclimate proxy data that point to high-latitude temperature amplification, significant decreases in sea ice and land ice, and the expansion of warmer climate biomes into higher latitudes. A major conundrum has been understanding what climate processes could have contributed to that mPWP condition when atmospheric CO₂ levels do not appear to have differed considerably from the present (380-405 ppmv). Many previous climate modeling efforts have struggled to reproduce the marine and terrestrial latitudinal temperature gradients suggested by the proxy data using close-to-current CO₂levels, suggesting that climate sensitivity in the Pliocene was influenced by dynamical considerations not previously captured by the models.

This presentation will show our most recent climate simulations of the Pliocene using the AR5/CMIP5 version of the GISS Earth System Model known as ModelE2-R, representing the NASA contribution to the Pliocene Model Intercomparison Project (PlioMIP). Our results display considerable improvement compared to simulations from earlier versions of the NASA GISS models, with improvement defined here as simulation results that more closely resemble the ocean temperature proxy data, as well as the U.S. Geological Survey’s PRISM3D reconstructions of mid-Pliocene climate. The major warming in the North Atlantic and Greenland-Iceland-Norwegian Sea demonstrated by these new simulations is, by far, the most concordant portrayal ever of this important geographic region by the GISS climate model. We believe that the continued development of key physical routines in the atmospheric component of the model, along with higher resolution and recent corrections to mixing parameterizations in the ocean component, have led to an Earth System Model that will produce more accurate simulations of recent Earth paleoclimates (Pliocene and younger), as well as projections of future climate.