The role of an interactive Greenland ice sheet in the coupled climate-ice sheet model EC-Earth-PISM

Abstract

Ice sheet processes are often simplified in global climate models as changes in ice sheets have been assumed to occur over long time scales compared to ocean and atmospheric changes. However, numerous observations show an increasing rate of mass loss from the Greenland Ice Sheet and call for comprehensive process-based models to explore its role in climate change. Here, we present a new model system, EC-Earth-PISM, that includes an interactive Greenland Ice Sheet. The model is based on the EC-Earth v2.3 global climate model in which ice sheet surface processes are introduced. This model interacts with the Parallel Ice Sheet Model (PISM) without anomaly or flux corrections. Under pre-industrial climate conditions, the modeled climate and ice sheet are stable while keeping a realistic interannual variability. In model simulations forced into a warmer climate of four times the pre-industrial CO2 concentration, the total surface mass balance decreases and the ice sheet loses mass at a rate of about 500 Gt/year. In the climate warming experiments, the resulting freshwater flux from the Greenland Ice Sheet increases 55% more in the experiments with the interactive ice sheet and the climate response is significantly different: the Arctic near-surface air temperature is lower, substantially more winter sea ice covers the northern hemisphere, and the ocean circulation is weaker. Our results indicate that the melt-albedo feedback plays a key role for the response of the ice sheet and its influence on the changing climate in the Arctic. This emphasizes the importance of including interactive ice sheets in climate change projections.

Remotely sensing potential climate change tipping points across scales

“…Remotely sensed data (Table 1 ) can provide crucial information to detect or validate tipping system interactions predicted by Earth system models and constrain their signs and strengths. Taking a previously identified example of a key interaction chain 46 , backed up by detailed model studies 125 : Rapid melting of the GrIS is already well-observed by altimetry and gravimetry and is predicted to increase the likelihood of crossing tipping points in the sub-polar gyre (SPG) circulation and the AMOC 124 —albeit dependent on model and resolution 126 – 128 . Associated changes in North Atlantic SSS, SST, and the SPG circulation should be observable through passive microwave, thermal infrared, and altimetry, respectively.…”

Rate-induced tipping cascades arising from interactions between the Greenland Ice Sheet and the Atlantic Meridional Overturning Circulation

“…the effects of a unidirectional coupling of the Greenland Ice Sheet towards the AMOC, was studied in terms of freshwater hosing experiments in general circulation models (GCMs) (Hu et al, 2009;Jungclaus et al, 2006;Stouffer et al, 2006;Swingedouw et al, 2013Swingedouw et al, , 2015Rahmstorf, 1995). In addition, experiments with coupled climate-ice sheet models under global warming were conducted (Fichefet et al, 2003;Ridley et al, 2005;Winguth et al, 2005;Swingedouw et al, 2006;Driesschaert et al, 2007;Mikolajewicz et al, 2007;Gierz et al, 2015;Golledge et al, 2019;Madsen et al, 2022). In general, the AMOC response to a freshwater flux associated with a GIS melting ranges from no significant weakening to an observable effect on the AMOC strength (Fichefet et al, 2003;Ridley et al, 2005;Winguth et al, 2005;Swingedouw et al, 2006;Jungclaus et al, 2006;Mikolajewicz et al, 2007;Driesschaert et al, 2007;Hu et al, 2009;Gierz et al, 2015;Golledge et al, 2019;Madsen et al, 2022).…”

“…In addition, experiments with coupled climate-ice sheet models under global warming were conducted (Fichefet et al, 2003;Ridley et al, 2005;Winguth et al, 2005;Swingedouw et al, 2006;Driesschaert et al, 2007;Mikolajewicz et al, 2007;Gierz et al, 2015;Golledge et al, 2019;Madsen et al, 2022). In general, the AMOC response to a freshwater flux associated with a GIS melting ranges from no significant weakening to an observable effect on the AMOC strength (Fichefet et al, 2003;Ridley et al, 2005;Winguth et al, 2005;Swingedouw et al, 2006;Jungclaus et al, 2006;Mikolajewicz et al, 2007;Driesschaert et al, 2007;Hu et al, 2009;Gierz et al, 2015;Golledge et al, 2019;Madsen et al, 2022). A collapse of the AMOC was found by Stouffer et al (2006) in response to a freshwater input of 1.0 Sv (10 6 m 3 s −1 ) for 100 years and by Fichefet et al (2003) in simulations of the 21st century climate.…”

“…However, freshwater inputs into the North Atlantic in such hosing experiments are highly idealized, vary in terms of their magnitude as well as spatial and temporal characteristics, and do not take into account the nonlinear melting characteristics of a tipping of the ice sheet on Greenland (Trusel et al, 2018;Robinson et al, 2012). In addition, the potential stabilizing effect of relatively colder temperatures in Greenland on the ice sheet (Jackson et al, 2015;Madsen et al, 2022) is not included. Many Earth system models are debated to be biased towards an AMOC that is too stable and hence may not be able to resolve its nonlinear behaviour due to missing couplings, processes and feedbacks, uncertainties in their representation, and biases in fluxes of salt and heat between ocean basins (Liu et al, 2017;Valdes, 2011;Weijer et al, 2019).…”

“…More specifically, the increasing Greenland mass loss (Shepherd et al, 2020;Mouginot et al, 2019; results in a freshwater input to the North Atlantic (Bamber et al, 2012(Bamber et al, , 2018Trusel et al, 2018), which may weaken the AMOC by decreasing seawater density and thereby weakening deep-water formation (Caesar et al, 2018;Rahmstorf et al, 2015;Golledge et al, 2019). The weakening or even tipping of the AMOC may be accompanied by a reduced northward heat transport and thus a relative cooling around Greenland (Vellinga andWood, 2002, 2008;Jackson et al, 2015;Madsen et al, 2022), which, in turn, may act in a stabilizing way on the melting processes of the Greenland Ice Sheet (Kriegler et al, 2009). There is still a knowledge gap regarding the effect of this positive-negative feedback loop on the overall stability of the coupled system of climatic tipping elements.…”