Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CoupledIceClim (Coupled climate and Greenland ice sheet evolution:past, present and future)

Teaser

The Greenland ice sheet has been losing mass at an accelerated pace during the last two decades, 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...

Summary

The Greenland ice sheet has been losing mass at an accelerated pace during the last two decades, 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, via changes in ocean and atmospheric circulations, surface characterization, etc. 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. On the other hand, 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, we contribute to the development and application 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.

Work performed

We have been working towards the release of the latest versions of the climate and ice sheet models in this project, as well as the ice sheet and climate coupling. In particular, we have have contributed to improved simulation of snow and ice melt and refreezing in the land component of the climate model, both for the Greenland ice sheet and Arctic tundra and ice caps. We have evaluated the downscaling procedure to use output of the climate model as boundary conditions for the much finer resolution ice sheet model. We have developed diagnostics for different components of the Earth System Model that are relevant to the science objectives of CoupledIceClim. We have tested, adjusted and evaluated advanced modules of the ice sheet model, such as the sliding and ice shelf simulators. We have used the ice sheet model to investigate multi-millenial oscilations in Greenland ice streams. We have contributed to the design, testing, adaptation and analysis of a novel model initialization procedure that provides an ice sheet equilibrated with the climate system as a starting condition to investigate the ice sheet sensitivity to external natural or anthropogenic forcings. This simulation will be used as starting point for a set of coupled ice sheet and climate simulations assessing the future evolution of the Greenland ice sheet at decadal to multi-century time-scales. We will provide these process-based projections of the future contribution of the Greenland ice sheet to sea level rise in time to be considered for inclusion in the next report of the International Panel for Climate Change (AR6).
We have also been working in the design and setup of a Last Glacial Maximum (21,000 to 18,000 years before present) simulation with interactive northern hemisphere ice sheets in the same climate/Earth System model that we use for future ice sheet evolution projections.
This simulation will have value in itself to investigate climate and ice sheet interactions at that time, and will also be the starting point to a coupled multi-millennia simulation of the massive deglaciation taking place between 18,000 and 10,000 years before present.

Final results

We are about to finalize the first simulation of the CESM with an interactive ice sheet, namely a spin-up to performed coupled ice-climate projections of the future contribution of the Greenland ice sheet to sea level rise. CoupledIceClim contributes to the Ice Sheet Model Intercomparison Project ISMIP6.
By the end of the project, we will extensively apply this new modeling tool to
- provide coupled ice-climate multi-century projections for idealized and historical-and IPCC scenario emissions
- assess the relative role of climate variability versus anthropogenic greenhouse warming in ongoing and future Greenland deglaciation rates
- assess the impact of Greenland deglaciation on ocean circulation and Arctic and regional climate change
- assess connections between future Arctic climate change and Greenland ice sheet changes
- assess the role of ice-climate interaction in explaining future and past deglaciation rates
- compare deglaciation processes in the recent past (the last deglaciation) and with ongoing climate change