The Greenland ice sheet is the largest freshwater reservoir in the northern hemisphere. During the last decades it has been losing mass at an accelerated pace, due to enhanced surface melt and ice discharge to the ocean, as a result respectively of atmospheric and ocean warming. This ice sheet is situated in the North Atlantic-Arctic region, which is highly vulnerable to anthropogenic climate change. At the same time, changes in the ice sheet affect the local, regional and global climate, through modified freshwater fluxes to the ocean, topographic change, and surface reflectivity (albedo) among others. It is desirable to comprehensively model the bi-directional interaction between ice sheet and climate change; however ice sheets are not yet standard components of the climate models used for climate projections and most of the projections on future ice sheet evolution are based on ice sheet model simulations forced with the output from climate models. To cover this gap, this project has contributed to the inclusion of an interactive Greenland ice sheet component of the Community Earth System Model to investigate ice sheet interactions with the climate system during past and ongoing deglaciations,
This work is relevant for projections of future sea level rise as well as polar and midlatitude climate, the latter due to the closeness of Greenland to sites of deep convection.
The overall objectives of the project are to contribute to advance understanding of ice sheet and climate interactions, to improve climate and ice sheet modelling, to contribute to model intercomparison projects, and to provide projections of future ice sheet evolution accounting for major feedbacks that contribute to the timing, rate and reversibility of deglaciation at century and multi-century time scales. Examples of such feedbacks and key interactions are albedo-melt feedback, elevation-melt feedback or ocean-ice-climate interaction.
From the application of the model to future Greenland ice sheet deglaciation we provided insights into the future evolution of the energy sources for surface melt, the refreezing capacity of the ice sheet, and the contributions of different ice sheet regions to the overall mass loss. We found that the southern half of the ice sheet rapidly contributes to sea level rise under anthropogenic greenhouse warming, due to its relatively warm summer climate. However, the northern margins are very sensitive to the warming at a later stage, once a critical level of overall warming is reached. We found that thermal radiation from the atmosphere is the primary contributor to melt at early stages of mass loss, however solar radiation becomes the primary contributor at later stages, due to large activation of the positive melt-albedo feedback. At a multicentury time-scale and under high greenhouse warming, the Greenland ice sheet transitions from marine margin with iceberg calving at the fjords to a terrestrial margin. The region that transitions the last is the southwest, in connection with large snowfall accumulation there from the North Atlantic weather systems.
The coupled model has shown the great potential for further research on climate and ice sheet interaction as it connects under the same umbrella the simulation of atmospheric, ocean and ice sheet surface and dynamical changes. This common frame permits to evaluate the impacts of specific changes in the climate system on Greenland ice sheet change, and viceversa, as well as the role of feedbacks in accelerating o decelerating ice shet mass loss.
