ALBERT

Description: Surface mass balance (SMB) is the builder of the Greenland ice sheet and the driver of ice dynamics. Quantifying the past, present and future state of SMB is important to understand the drivers and climatic processes that control SMB, and to both initialize and run ice sheet models which will help clarify sea level rise, and how likely changes in ice sheet extent feedback within the climate system. Regional climate models (RCMs) and climate reanalysis are used to quantify SMB estimates. Although different models have different spatial and temporal biases and may include different processes giving significant uncertainty in both SMB and the ice sheet dynamic response to it, all RCMs show a recent declining trend in SMB from the Greenland ice sheet, driven primarily by enhanced melt rates. Here, we present new simulations of the Greenland ice sheet SMB at 5 km resolution from the RCM HIRHAM5. The RCM is driven by the ERA-Interim reanalysis and the global climate model (GCM) EC-Earth v2.3 to make future projections for climate scenarios RCP8.5 and RCP4.5. Future estimates of SMB are affected by biases in driving global climate models, and feedbacks between the ice sheet surface and the global and regional climate system are neglected, likely resulting in significant underestimates of melt and precipitation over the ice sheet. These challenges will need to be met to better estimate the role climate change will have in modulating the surface mass balance of the Greenland ice sheet.

Description: Recent observations have indicated rapidly increasing mass loss from the Greenland Ice Sheet. To explore the interactions and feedbacks of the ice sheets in the climate system, it is important to develop coupled climate-ice sheet models. The integration of an ice sheet model in a global model is challenging, and, currently, relatively few climate models include a two-way coupling to a dynamical ice sheet model. In this work package, we have continued developing the coupled ice sheet-climate model system comprising the global climate model EC-Earth and the Parallel Ice Sheet Model (PISM) for Greenland. The new model system, EC-Earth3-GrIS, is upgraded to include the recent model versions, EC-Earth3 and PISM version 1.2. In addition, a new module has been developed to handle the exchange of information between the ice sheet model and EC-Earth using the OASIS3- MCT software interface. The new module reads output from the ice sheet model and exchanges the fields with the relevant EC-Earth components. The ice sheet mask and topography are provided to the atmosphere and land surface components. The heat and freshwater fluxes from basal melt and ice discharge are provided to the ocean module via the runoff-mapper that routes surface runoff into the ocean. The new module also prepares the forcing fields for the ice sheet model, i.e., subsurface temperature and surface mass balance. These fields are calculated in EC- Earth3 using a land ice surface parameterization, developed explicitly for the Greenland ice sheet. The parameterization contains a responsive snow and ice albedo scheme and includes land ice characteristics in the calculation of heat and energy transfer at the surface. Experiments with and without the land ice surface parameterization have been carried out for preindustrial and present-day conditions to assess the influence of the surface parameterization on the calculated surface mass balance. The results show that the ice sheet responds stronger and more realistically to forcing changes when the new surface parameterization is used. Besides the model development, the results from experiments with the first model version, EC- Earth-PISM, have been analyzed. These results stress that a decent surface scheme with a responsive snow albedo scheme is necessary for investigating mass balance changes of the Greenland Ice Sheet. Overall, our results indicate that the feedbacks induced by the interactive ice sheet have a significant influence on Arctic climate change under warming conditions. In warm scenarios where the CO2 level is raised to four times the preindustrial level, the coupled model has a colder Arctic surface, a fresher ocean, and more sea-ice in winter.

Description: Assessment of the projected future climate change relies on experiments using complex climate models (i.e., Earth System Models) that can realistically represent the Earth climate system. In this work package we made great efforts to enhance our capability in climate modelling using the family of the EC-Earth3 Earth System Model, and to increase our contribution to the international Coupled Model Intercomparison Project phase 6 (CMIP6). The contributions include performing another set of climate change simulations for the historical period (https://www.dmi.dk/fileadmin/Rapporter/2021/DMI_Report_21-33.pdf1850-2014) followed by four future scenarios (i.e., SSP5-8.5, SSP3-7.0, SSP2-4.5, SSp1-2.6, respectively) using the Earth System Model EC- Earth3-Veg; Extending the climate change simulation under the high-end emission scenario SSP5- 8.5 to year 2300; and performing the new CMIP6-endorsed CovidMIP aiming at assessing the climate impact of the emission reduction due to COVID19 pandemic. Archiving the CMIP6 experiment data following the CMIP6 standards and compliance on the Earth System Federation Grid (ESGF) data nodes is important to ensure the contribution to CMIP6 is available for scientists worldwide to access the data for a variety of applications from assessment and understanding of climate change, to studies of climate impacts and mitigation. We have worked a great deal to prepare the above mentioned and other CMIP6 simulation data for publishing on the DMI's ESGF data node. The processes involve in reformatting the simulation data into the CMIP standard and quality control the reformatted data to ensure their correctness. With our efforts and contributions to CMIP6, we have joined several multi-model multi-member ensemble analyses using the CMIP6 experiment ensembles. We have quantified the future climate changes under variety of future scenarios, and analyzed climate response to the COVID19 related emission reduction. We have also participated in the documentation of the EC-Earth3 model development and performance. These studies have led to a number of scientific papers. We foresee our contributed simulation ensembles, as subsets in the CMIP6 experiment ensembles, have contributed and will continue to contribute to many climate change assessments and studies for many years ahead. www.dmi.dk

Description: A prototype of a coupled climate-ice sheet model has been developed by the work package 1.1.3 "IskappeANT." The coupled system comprises the climate model EC-Earth and the Parallel Ice Sheet Model (PISM), representing Antarctica. Since the direct implementation of the involved processes, such as the implementation of ice shelf geometries, the ocean-ice shelf interaction, or the computation of the surface mass balance, would exceed the funding period of one year, we exploit state-of-the-art parameterizations. However, the robust system is open for enhancements in consecutive steps afterward and allows exploring scientific frontiers. The coupled system is one of the first state-of-the-art global climate models where the climate system interacts with the Antarctic ice sheet and its fringing ice shelves. This ambitious package includes these tasks: infrastructure to run the Parallel Ice Sheet Model (PISM) version 1.1.4 and version 1.2, setup and configuration of PISM to simulate Antarctica as a standalone model, coupling infrastructure, and first coupled simulations. This document describes the design decisions of the coupling. It presents the analysis of the preindustrial climate state in the Southern Ocean and across Antarctica. These states are subject to sufficiently large biases suggesting anomaly coupling between the climate model and the ice sheet model as an adequate coupling strategy.

Description: The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.