Efforts towards reconstructing ice sheets during the Pliocene

Abstract

Understanding Polar climate and the stability of high-latitude ice sheets is incredibly important in light of predicted future climate change and the polar amplification of warming.  The mid-Pliocene warm period (3.3 to 3.0 Ma) has been a highly investigated time in Earth history and it is well established that during this time period temperatures were warmer and CO2 levels were elevated compared to that of the pre-industrial era.  Changes in the polar cryosphere are a key driver of Pliocene climate change and reduced equator-to-pole temperature gradients. During the mid-Pliocene, estimates of sea level change between 5m and 25m have been reconstructed based on geological evidence. Best estimates of maximum sea level rise are around 20m, suggesting a significant contribution to sea level from both the Greenland and Antarctic Ice sheets is likely at certain intervals within the mid-Pliocene. Despite the uncertainties, Pliocene sea level has become a key target for ice sheet models trying to simulate ice sheet melt and a test-bed for ice loss physics.Alongside a series of modelling efforts to understand the broader Pliocene climate (PlioMIP1 and PlioMIP2), the Pliocene ice sheet modelling Intercomparison project (PLISMIP) was formed to investigate the dependency of ice sheet reconstructions on the specific climate or ice sheet model employed.   We detail investigations of ice sheet model parameterisations and initial conditions, climate model boundary conditions and the climate model used, and show the extent to which these impact our predictions of ice sheet configuration during the Pliocene. We consider the implications of having to prescribe an ice sheet configuration in large model intercomparison projects such as PlioMIP and how the results from PLISMIP and more recent independent ice sheet modelling work has influenced the experimental design in PlioMIP3 to include different ice sheet scenarios over Antarctica.  We also highlight key areas where there is the potential to use geological proxy data or employ enhanced modelling techniques to constrain our estimates of ice in a warmer world.