A technique for generating consistent ice sheet initial conditions for coupled ice sheet/climate models

A transient technique for generating ice sheet preindustrial initial conditions for long-term coupled ice sheet/climate model simulations is developed and demonstrated over the Greenland ice sheet using the Community Earth System Model (CESM). End-member paleoclimate simulations of the last glacial maximum, mid-Holocene optimum and the preindustrial are combined using weighting provided by ice core data time series to derive continuous energy-balance-model-derived surface mass balance and surface temperature fields, which are subsequently used to force a long transient ice sheet model simulation of the last glacial cycle, ending at the preindustrial. The procedure accounts for the evolution of climate through the last glacial period and converges to a simulated preindustrial ice sheet that is geometrically and thermodynamically consistent with the preindustrial CESM state, yet contains a transient memory of past climate. The preindustrial state generated using this technique notably improves upon the standard equilibrium spin-up technique, relative to observations and other model studies, although in the demonstration we present here, large biases remain due primarily to climate model forcing biases. Ultimately, the method we describe provides a clear template for generating initial conditions for ice sheets within a fully coupled climate model framework that allows for the effects of past climate history to be self-consistently included in long-term simulations of the fully coupled ice sheet/climate system