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

Abstract

Abstract.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 spinup 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.

The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

“…Force a stand-alone ice sheet model with a transient climate record obtained by interpolating between the climate extremes over the period of interest (often simulations of the pre-industrial and the Last Glacial Maximum; PI and LGM, respectively). The interpolation weights are typically derived from oxygen isotope ratios in Greenland and Antarctic ice cores (e.g., Charbit et al, 2007;Fyke et al, 2014).…”

Ice sheets as interactive components of Earth System Models: progress and challenges

“…First, the effect of past climates on the ice temperature profiles is partially excluded, particularly for lower ice layers. 61 Second, the parameters obtained by this procedure are not necessarily valid under different climate conditions. 86 Third, the resulting ice sheet has to equilibrate with the climate from the Earth System Model, and background trends are often big.…”

Author reply to reviewer comments

“…Published by Copernicus Publications on behalf of the European Geosciences Union. Larour et al, 2012), the Penn State Model (Pollard and De-Conto, 2012), BISICLES (Cornford et al, 2013), Elmer-Ice (Gagliardini et al, 2013), and MPAS-Albany Land Ice (MALI; Tezaur et al, 2015;Hoffman et al, 2018). Higherorder models have performed well for standard test cases (Pattyn et al, 2008;Pattyn et al, 2012) and have been applied to many scientific problems.…”