The PlioMIP and PRISM Projects: Mid- and High-Latitude Warmth during the Mid-Pliocene Warm Period

Abstract:

The mid-Pliocene warm period (mPWP, 3.264 to 3.025 Ma) has been considered a possible analog for the future long-term consequences of anthropogenic greenhouse gas changes. Atmospheric carbon dioxide concentrations for this period have been estimated to be approximately 350 to 450 ppmv. We have now nearly surpassed globally the mid-point of this range and could surpass 450 ppmv by shortly after year 2030 in the most dire pathway of future emissions. In Phase I of the Pliocene Model Intercomparison Project (PlioMIP), twelve coupled climate models simulated the mPWP time slab. These models could not reproduce the mid- and high-latitude Northern Hemisphere warmth indicated by the PRISM3 dataset. Models suggest that Arctic sea ice, particularly no summer sea ice and much reduced winter sea ice, rather than changes in the Atlantic Meridional Overturning Circulation and associated ocean heat transport, are key for reproducing the high-latitude warmth.

Planning for the modeling experiments, CMIP6, which will contribute to the IPCC AR6 in 2019, is underway. PlioMIP Phase II and PRISM4 have selected a time-slice centered at 3.205 Ma (3.204 to 3.207 Ma) to better constrain the comparisons between models and data and help reduce uncertainties associated with forcings incorporated into the model designs. In this talk, we will introduce the PlioMIP II protocols. We will also discuss those differences in the paleogeography and forcings from modern that may need to be considered when assessing the climate model simulations against proxy indicators of mid- and high-latitude temperature and the Pliocene as an analogue for the future. The model experiments included in PlioMIP II and PRISM4 dataset will be important not only for Pliocene4Future but also Pliocene4Pliocene, thus advancing our knowledge of this period in its own right.