Accelerated Greenland Ice Sheet Mass Loss under High Greenhouse Gas
Forcing as Simulated by the Coupled CESM2.1-CISM2.1
Abstract
The Greenland ice sheet (GrIS) has been losing mass in the last several
decades, and is currently contributing around 0.7 mm sea level
equivalent (SLE) yr-1 to global mean sea level rise (SLR). As ice sheets
are integral parts of the Earth system, it is important to gain
process-level understanding of GrIS mass loss.
This paper presents an idealized high-forcing simulation of 350 years
with the Community Earth System Model version 2.1 (CESM2.1) including
interactively coupled, dynamic GrIS with the Community Ice Sheet Model
v2.1 (CISM2.1). From pre-industrial levels (287 ppmv), the CO2
concentration is increased by 1% yr-1 till quadrupling (1140 ppmv) is
reached in year 140. After this, the forcing is kept constant.
Global mean temperature anomaly of 5.2 K and 8.5 K is simulated by years
131–150 and 331-150, respectively. The North Atlantic Meridional
Overturning Circulation strongly declines, starting before GrIS runoff
substantially increases. The projected GrIS contribution to global mean
SLR is 107 mm SLE by year 150, and 1140 mm SLE by year 350.
The accelerated mass loss is driven by the SMB. Increased long-wave
radiation from the warmer atmosphere induces an initial slow SMB
decline. An acceleration in SMB decline occurs after the ablation areas
have expanded enough to trigger the ice-albedo feedback. Thereafter,
short-wave radiation becomes an increasingly important contributor to
the melt energy. The turbulent heat fluxes further enhance melt and the
refreezing capacity becomes saturated. The global mean temperature
anomaly at the start of the accelerated SMB decline is 4.2 K.