An Intra-European Fellowship (IEF) project funded by the European 7th Framework Programme
Global sea levels are expected to increase on the order of several meters in the medium to long term under global warming, which will have large impacts on the millions of people who live in coastal areas. The largest contribution to sea level rise will come from the continental ice sheets, Greenland and Antarctica. Refining the currently highly uncertain estimates of the magnitude and timing of ice sheet mass loss is critical for adaptation strategies and minimization of losses. This project aimed to improve our understanding of the sensitivity of the ice sheets to climate change from an integrated Earth systems perspective and to reduce uncertainty in sea level rise projections.
Outcome of the project
A flexible, user-oriented modeling framework has been developed and tested, including a set of key generic tools that facilitate the user in coupled geophysical model simulations. To this end, several stand-alone FORTRAN and Python libraries have been developed, validated and documented. A very flexible modeling framework has been built around the above utilities that is easy to use and allows the coupling of any model components in a straightforward and encapsulated way.
Significant improvements to the regional climate model REMBO were implemented in Work Package 1. This model is used for calculating the change in the surface mass balance of the Greenland ice sheet under climate change. A new precipitation scheme was introduced that improves both the spatial distribution of simulated precipitation compared with observations, as well as the seasonality. Furthermore, the previous empirical equation for melt has been replaced by a new full energy balance scheme. This step represents a refinement of the resolution and ability of the model to reproduce results from more computationally intensive regional climate models (RCMs), with a minimal change in computational cost.
Work package 2 consisted of investigation of the past evolution of the Greenland ice sheet including Marine Interglacial Stage (MIS) 11 and MIS-5, the two most recent periods when the ice sheet was expected to be smaller and the climate warmer than today, as well as the initial glaciation of Greenland about 3 Ma before today. Results show that while MIS-11 may not have been warmer than MIS-5, it was long enough to destabilize and melt most of the ice sheet. It was also shown that Greenland only originally glaciated originally after CO2 dropped below a certain threshold. These findings have important implications for future climate change – it is critical to keep global warming to as low as possible in order to slow and/or halt the decline of the Greenland ice sheet.
In work package 3, the future evolution of the Greenland ice sheet and its sensitivity to climate change were studied. It was shown that the long-term consequences of melting will increase non-linearly with temperature. The melting of the Greenland ice sheet will self-amplify owing to positive feedbacks, particularly that between surface elevation and temperature. The threshold leading to complete melting of the Greenland ice sheet can be expressed in terms of cumulative CO2 emissions, and with the newly calibrated model, we find that the threshold for melting is lower than previously believed. In addition, it was shown that current melting of the Greenland ice sheet may play role in the observed slowdown of the Atlantic Meridional Circulation (AMOC).
A simple interface for reading and writing data to and from NetCDF files.
– coordinates: https://github.com/alex-robinson/coordinates
A package to manage gridded data and sets of points on specific coordinate systems. Functions include oblique stereographic projection and mapping between different coordinate systems. This package also includes interpolation routines (linear, 1D-spline) that can be used for space and time.
– ensembles: https://github.com/alex-robinson/ensembles
A package to translate an ensemble of individual model runs into a concise set of ensemble-based output.
A Fortran module to provide an improved, more flexible interface to Namelist formatted parameter files.
A set of Python functions and master script that manages all aspects of creating a new simulation (or batch set of simulations), including directory creation, parameter modification and submission of jobs to a computing cluster.
– insolation: https://github.com/alex-robinson/insol
A module to calculate daily insolation at any latitude for any time over the last 5 Million years to the future 1 Million years.
– vecode: https://github.com/alex-robinson/vecode
A module to calculate the equilibrium vegetation cover given the monthly climatological data, based on empirical relationships.
– ice_data: https://github.com/alex-robinson/ice_data
A data repository holding all relevant known data sets for ice sheet modeling, processed to regional grids (ie, ready to be input into an ice sheet model).
Robinson, A. and Perrette, M.: NCIO 1.0: a simple Fortran NetCDF interface, Geosci. Model Dev., 8, 1877-1883, https://doi.org/10.5194/gmd-8-1877-2015, 2015.
Rahmstorf, S., Box, J. E., Feulner, G., Mann, M. E., Robinson, A., Rutherford, S. and Schaffernicht, E. J.: Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change, 1-6, doi:10.1038/nclimate2554, 2015.
Calov, R., Robinson, A., Perrette, M. and Ganopolski, A.: Simulating the Greenland ice sheet under present-day and palaeo constraints including a new discharge parameterization, The Cryosphere, 9, 179-196, doi:10.5194/tc-9-179-2015, 2015.
Willeit, M., Ganopolski, A., Calov, R., Robinson, A. and Maslin, M.: The role of CO2 decline for the onset of Northern Hemisphere glaciation, Quaternary Science Reviews, 119, 22-34, doi:10.1016/j.quascirev.2015.04.015, 2015.
Banderas, R., Alvarez-Solas, J., Robinson, A. and Montoya, M.: An interhemispheric mechanism for glacial abrupt climate change, Climate Dynamics, 44, 2897-2908, doi:10.1007/s00382-014-2211-8, 2014.
Robinson, A. and Goelzer, H.: The importance of insolation for paleo ice sheet modeling, The Cryosphere, 8, 1419-1428, doi:10.5194/tc-8-1419-2014, 2014.
Levermann, A., Clark, P., Marzeion, B., Milne, G. A., Pollard, D., Radić, V. and Robinson, A.: The multimillennial sea-level commitment of global warming, Proceedings of the National Academy of Sciences of the United States of America, 110, 34, 13745-13750, doi:10.1073/pnas.1219414110, 2013.
Alvarez-Solas, J., Robinson, A., Montoya, M. and Ritz, C.: Iceberg discharges of the last glacial period driven by oceanic circulation changes, Proceedings of the National Academy of Sciences of the United States of America, doi:10.1073/pnas.1306622110, 2013.