Eemian Greenland SMB strongly sensitive to model choice Andreas Plach, Kerim Nisancioglu, Sébastien Le Clec’H, Andreas Born, Petra Langebroek, Chuncheng Guo, Michael Imhof, Thomas Stocker To cite this version: Andreas Plach, Kerim Nisancioglu, Sébastien Le Clec’H, Andreas Born, Petra Langebroek, et al.. Eemian Greenland SMB strongly sensitive to model choice. Climate of the Past, European Geosciences Union (EGU), 2018, 14 (10), pp.1463-1485. 10.5194/cp-14-1463-2018. hal-02975965 HAL Id: hal-02975965 https://hal.archives-ouvertes.fr/hal-02975965 Submitted on 26 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Clim. Past, 14, 1463–1485, 2018 https://doi.org/10.5194/cp-14-1463-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Eemian Greenland SMB strongly sensitive to model choice Andreas Plach1, Kerim H. Nisancioglu1,2, Sébastien Le clec’h3,4, Andreas Born1,5,6, Petra M. Langebroek7, Chuncheng Guo7, Michael Imhof8,5, and Thomas F. Stocker5,6 1Department of Earth Science, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway 2Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway 3Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France 4Earth System Science and Department Geografie, Vrije Universiteit Brussel, Brussels, Belgium 5Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland 6Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland 7Uni Research Climate and Bjerknes Centre for Climate Research, Bergen, Norway 8Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Zürich, Switzerland Correspondence: Andreas Plach ([email protected]) Received: 3 July 2018 – Discussion started: 9 July 2018 Revised: 20 September 2018 – Accepted: 5 October 2018 – Published: 19 October 2018 Abstract. Understanding the behavior of the Greenland ice SMB. Whether model resolution or the SMB method is most sheet in a warmer climate, and particularly its surface mass important depends on the climate state and in particular the balance (SMB), is important for assessing Greenland’s po- prevailing insolation pattern. We suggest that future Eemian tential contribution to future sea level rise. The Eemian in- climate model intercomparison studies should include SMB terglacial period, the most recent warmer-than-present pe- estimates and a scheme to capture SMB uncertainties. riod in Earth’s history approximately 125 000 years ago, pro- vides an analogue for a warm summer climate over Green- land. The Eemian is characterized by a positive Northern Hemisphere summer insolation anomaly, which complicates 1 Introduction Eemian SMB calculations based on positive degree day esti- mates. In this study, we use Eemian global and regional cli- The projections of future sea level rise remain uncertain, es- mate simulations in combination with three types of SMB pecially the magnitude and the rate of the contributions from models – a simple positive degree day, an intermediate com- the Greenland ice sheet (GrIS) and the Antarctic ice sheet plexity, and a full surface energy balance model – to evaluate (Church et al., 2013; Mengel et al., 2016). In addition to im- the importance of regional climate and model complexity for proving dynamical climate models, it is important to test their estimates of Greenland’s SMB. We find that all SMB mod- ability to simulate documented warm climates. Past inter- els perform well under the relatively cool pre-industrial and glacial periods are relevant examples as these were periods late Eemian. For the relatively warm early Eemian, the dif- of the recent past with relatively stable warm climates per- ferences between SMB models are large, which is associated sisting over several millennia. They provide benchmarks for with whether insolation is included in the respective mod- testing key dynamical processes and feedbacks under a dif- els. For all simulated time slices, there is a systematic dif- ferent background climate state. Quaternary interglacial pe- ference between globally and regionally forced SMB mod- riods exhibit a geological configuration similar to today (e.g., els, due to the different representation of the regional climate gateways and topography) and have been frequently used as over Greenland. We conclude that both the resolution of the analogues for future climates (e.g., Yin and Berger, 2015). simulated climate as well as the method used to estimate the In particular, the most recent interglacial period, the Eemian SMB are important for an accurate simulation of Greenland’s (approximately 130 to 116 ka) has been used to better under- stand ice sheet behavior during a warm climate. Published by Copernicus Publications on behalf of the European Geosciences Union. 1464 A. Plach et al.: Eemian Greenland SMB strongly sensitive to model choice Compared to the pre-industrial period, the Eemian is es- Ganopolski and Robinson, 2011; Lunt et al., 2013). However, timated to have had less Arctic summer sea ice, warmer the higher availability of proxy data compared to preced- Arctic summer temperatures, and up to 2 ◦C warmer annual ing interglacial periods makes the Eemian a better candidate global average temperatures (CAPE Last Interglacial Project to investigate warmer conditions over Greenland (Yin and Members, 2006; Otto-Bliesner et al., 2013; Capron et al., Berger, 2015). Furthermore, Masson-Delmotte et al.(2011) 2014). Ice core records from NEEM (the North Greenland found a similar Arctic summer warming over Greenland with Eemian Ice Drilling project in northwest Greenland) indi- the higher Eemian insolation as for a future doubling of at- ◦ cate a local warming of 8:5 ± 2:5 C(Landais et al., 2016) mospheric CO2 given fixed pre-industrial insolation. compared to pre-industrial levels. However, total gas con- In this study, we assess the importance of the represen- tent measurements from the deep Greenland ice cores GISP2, tation of small-scale climate features and the impact of the GRIP, NGRIP, and NEEM indicate that the Eemian surface SMB model complexity (i.e., using three SMB models) when elevation at these locations was no more than a few hun- calculating the SMB for warm climates such as the Eemian. dred meters lower than present (Raynaud et al., 1997; NEEM High-resolution pre-industrial and Eemian Greenland cli- community members, 2013). Proxy data derived from coral mate is provided by downscaling global time slice simula- reefs show a global mean sea level at least 4 m above the tions with the Norwegian Earth System Model (NorESM) present level (Overpeck et al., 2006; Kopp et al., 2013; Dut- using the regional climate model (RCM) MAR (Modèle At- ton et al., 2015). mosphérique Régional). Based on these global and regional Several studies have investigated the Eemian GrIS. Nev- climate simulations, three different SMB models are applied, ertheless, there is no consensus on the extent to which the including (1) a simple, empirical PDD model, (2) an interme- GrIS retreated during the Eemian. Scientists have applied diate complexity SMB model explicitly accounting for solar ice core reconstructions (e.g., Letréguilly et al., 1991; Greve, insolation, as well as (3) the full SEB model implemented in 2005) and global climate models (GCMs) of various com- MAR. plexities (e.g., Otto-Bliesner et al., 2006; Stone et al., 2013) A review of previous Eemian GrIS studies is given in combined with regional models (e.g., Robinson et al., 2011; Sect.2, followed by the models, data, and experiment de- Helsen et al., 2013) to create Eemian temperature and precip- sign in this study discussed in Sect.3. The results of the pre- itation forcing over Greenland. Based on these reconstructed industrial and Eemian simulations are presented in Sects.4 or simulated climates, different models have been used to cal- and5, respectively. The challenges and uncertainties are dis- culate the surface mass balance (SMB) in Greenland for the cussed in Sect.6. Finally, a summary of the study is given in Eemian. The vast majority of these studies use the positive Sect.7. degree day (PDD) method introduced by Reeh(1989), which is based on an empirical relation between melt and temper- ature. PDD has been shown to work well under present-day 2 Comparison of previous Eemian conditions (e.g., Braithwaite, 1995) and has been widely used Greenland studies by the community due to its simplicity and ease of integra- tion with climate and ice sheet models. More recent studies Scientists started modeling the Eemian GrIS more than employ physically based approaches to calculate the SMB, 25 years ago (Letréguilly et al., 1991). However, a clear pic- ranging from empirical models (e.g., Robinson et al., 2010) ture of the minimum extent and the shape of the Eemian to surface energy balance (SEB) models (e.g., Helsen et al., GrIS is still missing. The estimated contributions from the 2013). GrIS to the Eemian sea level rise differ largely and vary be- It is important to note that the relatively warm summer tween 0.4 and 5.6 m. An overview of previous studies and (and cold winter) in the Northern Hemisphere during the their estimated Eemian sea level rise from Greenland is given early Eemian (130–125 ka) was caused by a different insola- in Fig.1. tion regime compared to today, not increased concentrations Early studies used Eemian temperature anomalies derived of greenhouse gases (GHGs) which are primarily respon- from ice core records and perturbed a present-day temper- sible for the recent observed global warming (e.g., Lange- ature field in order to get estimated Eemian temperatures broek and Nisancioglu, 2014).