Neglecting ice-atmosphere interactions underestimates ice sheet melt in millennial-scale deglaciation simulations
Dynamic and thermodynamic interactions between the atmosphere and underlying ice sheets are generally not represented in the traditional one-way boundary condition forcing used to drive ice sheet models. This shortcoming is investigated through a series of idealized millennial-scale deglaciation simulations designed to isolate the mechanisms regulating the deglaciation timescale of the Laurentide ice sheet. Sensitivity experiments indicate that the conventional use of one-way (non-interactive) atmospheric forcing fields leads to an unrealistically insensitive melt response in the ice sheet model even when atmospheric carbon dioxide is set to modern preindustrial levels and Earth's angle of obliquity is set to its early Holocene value. A more realistic deglaciation timescale is obtained only through the application of a new two-way (interactive) asynchronous ice-atmosphere coupling scheme and a seasonal ice albedo parameterization that accounts for the observed darkening of ice in the moist summertime ablation zone.