Abstract
Earlier large-scale Greenland ice sheet sea-level projections (e.g., those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of the initMIP-Greenland intercomparison exercise is to compare, evaluate and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project - phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of 1) the initial present-day state of the ice sheet and 2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly), and should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap, but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.
Highlights
Ice sheet model intercomparison exercises have a long history, going back to the advent of large-scale ice sheet models in the early 1990s
Calculating the root mean square error (RMSE) based on the log of the velocities instead (Fig. 7b) results in a slightly different picture, because errors in high velocities typically occurring at the margins over a relatively small fraction of the ice sheet area are weighted less
We note that an alternative choice of metric would be one that accounts for spatial variation in observational uncertainty, such as standardised Euclidean distance
Summary
Ice sheet model intercomparison exercises have a long history, going back to the advent of large-scale ice sheet models in the early 1990s. Payne et al, 2000; Calov et al, 2010; AsayDavis et al, 2016), and (3) experiments of models applied to real ice sheets (e.g. Shannon et al, 2013; Edwards et al, 2014b; Bindschadler et al, 2013; Nowicki et al, 2013a, b). ISMIP6 is the first ice sheet model intercomparison that is fully integrated within CMIP This is an improvement to earlier initiatives like ice2sea (Gillet-Chaulet et al, 2012; Shannon et al, 2013; Goelzer et al, 2013; Edwards et al, 2014a, b) and SeaRISE (Sea-level Response to Ice Sheet Evolution; Bindschadler et al, 2013; Nowicki et al, 2013a, b), which were lagging one iteration behind in terms of applied climate forcing. More information on ISMIP6 can be found in the description paper (Nowicki et al, 2016) and on the Climate and Cryosphere (CliC)-hosted webpage (http: //www.climate-cryosphere.org/activities/targeted/ismip6)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
