Warm Greenland during the last interglacial: the role of regional changes in sea ice cover

Abstract

Abstract. The last interglacial, also known as the Eemian, is characterized by warmer than present conditions at high latitudes. This is implied by various Eemian proxy records as well as by climate model simulations, though the models mostly underestimate the warming with respect to proxies. Simulations of Eemian surface air temperatures (SAT) in the Northern Hemisphere extratropics further show large variations between different climate models, and it has been hypothesized that this model spread relates to diverse representations of the Eemian sea ice cover. Here we use versions 3 and 4 of the Community Climate System Model (CCSM3 and CCSM4) to highlight the crucial role of sea ice and sea surface temperatures changes for the Eemian climate, in particular in the North Atlantic sector and in Greenland. A substantial reduction in sea ice cover results in an amplified atmospheric warming and thus a better agreement with Eemian proxy records. Sensitivity experiments with idealized lower boundary conditions reveal that warming over Greenland is mostly due to a sea ice retreat in the Nordic Seas. In contrast, sea ice changes in the Labrador Sea have a limited local impact. Changes in sea ice cover in either region are transferred to the overlying atmosphere through anomalous surface energy fluxes. The large-scale spread of the warming resulting from a Nordic Seas sea ice retreat is mostly explained by anomalous heat advection rather than by radiation or condensation processes. In addition, the sea ice perturbations lead to changes in the hydrological cycle. Our results consequently imply that both temperature and snow accumulation records from Greenland ice cores are sensitive to sea ice changes in the Nordic Seas but insensitive to sea ice changes in the Labrador Sea. Moreover, the simulations suggest that the uncertainty in the Eemian sea ice cover accounts for 1.6 • C of the Eemian warming at the NEEM ice core site. The estimated Eemian warming of 5 • C above present day based on the NEEM δ 15 N record can be reconstructed by the CCSM4 model for the scenario of a substantial sea ice retreat in the Nordic Seas combined with a reduced Greenland ice sheet.

Attributing Greenland Warming Patterns to Regional Arctic Sea Ice Loss

“…During summer, Rennermalm et al (2009) also find local correlations between sea ice cover and GrIS melt on selected parts of the east coast. Atmospheric model studies (Merz et al, 2016;Screen, 2017) also show that GS ice loss causes warming on the eastern and southern parts of Greenland; Merz et al (2016) even illustrate how GS ice loss may cause atmospheric circulation changes that causes substantial warming over Greenland (albeit under Last Interglacial climate conditions).…”

Eemian Greenland SMB strongly sensitive to model choice

“…MAR is a regional atmospheric model fully coupled to the land surface model SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer) which includes a detailed snow energy balance model (Gallée and Duynkerke, 1997). The atmospheric part of MAR uses the solar radiation scheme of Morcrette et al (2008) and accounts for the atmospheric hydrological cycle (including a cloud microphysical model) based on Lin et al (1983) and Kessler (1969). The snow-ice part of MAR is derived from the snowpack model Crocus (Brun et al, 1992).…”

Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

“…Several attempts to solve this paradox have been made by suggesting possible biases in the interpretation of the relationship between isotope ratio and temperature, which may not be assumed temporally and spatially constant (e.g. Merz et al, 2014;Sjolte et al, 2014;Steen-Larsen et al, 2014;Masson-Delmotte et al, 2015) or may be affected by changes in the precipitation regime and sea ice conditions (Merz et al, 2016;Pedersen et al, 2016). From a modelling point of view, the decisive question is over what spatial extent and when during the year the temperature reconstruction (and possible future reinterpretations) for the NEEM site should be assumed.…”

“…Several studies have therefore attempted to identify possible biases in the NEEM reconstructions (e.g. van de Merz et al, 2014Merz et al, , 2016Sjolte and Hoffmann, 2014;Steen-Larsen et al, 2014;Masson-Delmotte et al, 2015;Pedersen et al, 2016). Furthermore, the minimum extent and margin position of the north-eastern part of the ice sheet is not well constrained, leaving room for alternative retreat scenarios (e.g.…”