The Arctic is warming at a rate greater than the global average, summer sea ice extent is reaching new minimums, and the Greenland ice sheet is now losing more mass than it is gaining. Earth System Models indicate that these trends will continue in the future, more or less, depending on the scenario of future emissions and land use that the world follows over the next centuries. The past can be used to inform what could happen in the future. In this talk, I will present two simulations with the Community Earth System Model (CESM2) for a past warm period, the Last Interglacial 129-116 thousand years ago [ka], a time period when geological records indicate that the Arctic was warmer than present, with boreal forests replacing tundra to the Arctic Ocean in parts of Eurasia and North America and with a smaller Greenland ice sheet. Sea level was 6-9 meters higher than present, though with uncertainties on the rate of sea level rise and the contributions of the Greenland versus Antarctic ice sheets. The first simulation is the CMIP6 Tier 1 simulation with a static Greenland ice sheet, forced with the strong astronomically induced seasonal forcing of insolation for 127ka compared to present. The second simulation, still ongoing, includes two-way coupling to the CISM2.1 model of the Greenland ice sheet and forced with evolving insolation anomalies and vegetation from 127ka to 121ka. Our comparison of these simulations to geological records will allow assessment of our confidence in companion CESM2-CISM2 simulations being completed for 1%CO2to4x and SSP585 for CMIP6 and ISMIP6.