Natural variability in surface conditions of the Greenland ice sheet

Changes in the mass of the Greenland ice sheet (GrIS) influence global sea levels. Thus, in order to predict future sea level rise, we must understand the role that climate change plays in altering the GrIS mass balance. However, GrIS mass variations over the past several centuries is not well known. In particular, the role of natural forcing in generating variability in the mass balance of the Greenland ice sheet has not been established. Until these natural climate variations are understood, it will be difficult to anticipate what role anthropogenic greenhouse gases have on GrIS-induced sea level rise. In order to address these issues, we have performed a suite of global, atmosphere-ocean general circulation model simulations of the past millennium to establish the connection between Arctic climate conditions and temperature and precipitation changes over the Greenland ice sheet.

We have created five historical simulations from years 850 to 2000 using the Community Climate System Model 3 at two different spectral resolutions of T42 and T85. These simulations use boundary conditions consistent with those produced for the Paleoclimate Modelling Intercomparison Project Phase 3, including two different volcanic reconstructions and time-varying orbital forcing. We have also extended some of these simulations into the future using a selection of representative concentration pathways from the Coupled Model Intercomparison Project Phase 5. Over the historical period, we have examined how temperatures and precipitation over the Greenland ice sheet have varied with Arctic sea ice extent, the North Atlantic Oscillation Index, the Atlantic Meridional Overturning Circulation and its connection to the Atlantic Multi-decadal Oscillation, the El Nino-Southern Oscillation, volcanic aerosol loading, total solar irradiance changes, and anthropogenic greenhouse-gas concentrations. We will present an analysis of which correlations are most important in our simulations, and at which time scales. We will also discuss whether these connections remain constant throughout the historical and future periods, or whether they change with the changing climate.