EGU2020-5912
https://doi.org/10.5194/egusphere-egu2020-5912
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial

Bas de Boer1, Aurélien Quiquet2, Pepijn Bakker1, and Didier Roche1,2
Bas de Boer et al.
  • 1VU Amsterdam, Earth and Climate Cluster, Faculty of Science, Amsterdam, Netherlands (bas.de.boer@vu.nl)
  • 2Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France

Glacial-interglacial changes of the Earth's climate are largely controlled by internal mechanisms that drive changes in greenhouse gases and ice sheets. In this study, we present model experiments of the penultimate deglaciation into the the last interglacial period, obtained with the Earth system model of intermediate complexity iLOVECLIM (v. 1.1.4). We show experiments with an imposed ice-sheet scenario together with initial results with both North and South interactive ice sheets using the GRISLI (v. 2.0) 3-D ice-sheet model. To this aim, we use a recently developed dynamical downscaling procedure to compute temperature and precipitation fields from the relative low resolution atmospheric model grid (T21, ~5.6º) to the GRISLI spherical grids of both the Northern Hemisphere and Antarctica (both 40 x 40 km). We investigate the separate impact of variations of greenhouse gases (GHG), orbital parameters and ice sheets on glacial-interglacial climate change over the past 240 kyr. Using prescribed greenhouse gases or ice sheets induce comparable changes in global mean temperature. Greenhouse gases, predominantly CO2, mainly have a global impact through radiative forcing on atmospheric temperatures. On the other hand, ice sheets have a more regional impact over the Northern Hemispheric (NH) continents and Antarctica during glacial times. Henceforth, polar amplification is more pronounced during glacial periods following large ice-sheet induced changes. Overall these results are comparable to other studies using a similar experimental design. In order to initiate the coupling between the ice sheets and climate model, we perform a large ensemble of experiments to calibrate ice-sheet model parameters for the present day. We will present how the optimal settings for the two ice-sheet regions are selected, based on a comparison with the present-day ice sheets on Antarctica and Greenland. For the coupling, iLOVECLIM generates downscaled SMB, surface temperatures, ocean temperature and salinity, and GRISLI provides surface elevation and ice extent, the coupling interval is 5 years. These experiments are started during the penultimate glacial maximum. We initialize the coupled iLOVECLIM - GRISLI experiments from a climatic forcing experiment using prescribed greenhouse gases and ice sheets, and generate a spin-up simulation of GRISLI using the optimal settings for three different time points at 136, 135 and 134 kyr ago. Initial experiments show a clear linkage between changes in ice sheets, sea ice and ocean circulation. Following the forced rise in atmospheric GHGs, the magnitude of retreat varries between ice sheets, related to location and insolation change (which increases for the NH but decreased for Antarctica). Moreover, sea ice both decrease following GHGs increase, and vary more in phase with global mean temperature.

How to cite: de Boer, B., Quiquet, A., Bakker, P., and Roche, D.: Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5912, https://doi.org/10.5194/egusphere-egu2020-5912, 2020

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Display material version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-5912, Lennert Stap, 06 May 2020

    Hello Bas,

    Thanks for showing these interesting results! I have some questions, in particular on slide 5. LOVECLIM shows equal contributions of ice sheet and GHG changes to the total temperature perturbation, whereas using CLIMBER-2 we saw a larger effect of ice sheet changes. Could be because in CLIMBER-2, we neglected non-CO2 GHGs, or because the climate sensitivity (ECS) of LOVECLIM is higher. What is the ECS of LOVECLIM? 

    Furthermore I'm curious what effect is dominating the influence of ice sheet changes, albedo changes or surface height changes? What is the typical albedo diffference between glaciated and unglaciated land?

    And finally, how large is the synergy between GHG and land ice changes? Judging by eye, it looks like it could be negative.

    Regards, Lennert

    • AC1: Reply to CC1, User deleted account, 06 May 2020

      Hi Lennert,

      Thanks for the questions. Yes have not looked into detail here, but we do include all GHGs, although iLOVECLIM transfers all change towards CO2 equivalent. ECS is quite low actually, see Loutre et al. I have calculated it myself and the default ECS in the runs shown here is about 1.7-1.8 K to a doubling of CO2.

      Don't know what dominates, but both are included naturally. Difference I'll have to check.

      Yes sometimes it negative. see attached figure (I think this is what you mean). 

    • AC2: Reply to CC1, User deleted account, 06 May 2020

      Hi Lennert,

      Albedo if ice sheets is 0.85, the typical changes I see over NH continents (difference between LGM and PD) is between 0.50 and 0.60.

      Cheers,

      Bas

      • CC2: Reply to AC2, Lennert Stap, 06 May 2020

        Thanks for the additional info. It seems the residuals/synergies in your LOVECLIM simulations are considerably larger than in the CLIMBER-2 results, but I can't see a clear pattern in them. Also, I'm wrapping my head around what negative synergy means: less strong GHG effects in a more glaciated world (i.e. state-dependent climate sensitivity)? Or less strong ice sheet effects in lower-GHG climates?

        • AC3: Reply to CC2, User deleted account, 06 May 2020

          Hi Lennert,

          Well some bits are feedbacks within the system. GHG have obviously sea-ice effects with add to the response (i.e. cooling) and perhaps snow-cover or vegetation. This effects is also in the case for the run with only ice sheets. When combining both (ALL), this effect is there, a bit bigger perhaps, but it cannot be summed up.. And must be other feedbacks as well.

          Bas

          • CC3: Reply to AC3, Lennert Stap, 06 May 2020

            I see. Actually, negative synergies make a lot of sense then.