Hypersensitivity of glacial summer temperatures in Siberia

Abstract

Climate change in Siberia is currently receiving a lot of attention because large permafrost-covered areas could provide a strong positive feedback to global warming through the release of carbon that has been sequestered there on glacial-interglacial timescales. Geological evidence and climate model experiments show that the Siberian region also played an exceptional role during glacial periods. The region that is currently known for its harsh cold climate did not experience major glaciations during the last ice age, including its severest stages around the Last Glacial Maximum (LGM). On the contrary, it is thought that glacial summer temperatures were comparable to the present day. However, evidence of glaciation has been found for several older glacial periods.We combine LGM experiments from the second and third phases of the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) with sensitivity experiments using the Community Earth System Model (CESM). Together, these climate model experiments reveal that the intermodel spread in LGM summer temperatures in Siberia is much larger than in any other region of the globe and suggest that temperatures in Siberia are highly susceptible to changes in the imposed glacial boundary conditions, the included feedbacks and processes, and to the model physics of the different components of the climate model. We find that changes in the circumpolar atmospheric stationary wave pattern and associated northward heat transport drive strong local snow and vegetation feedbacks and that this combination explains the susceptibility of LGM summer temperatures in Siberia. This suggests that a small difference between two glacial periods in terms of climate, ice buildup or their respective evolution towards maximum glacial conditions can lead to strongly divergent summer temperatures in Siberia, allowing for the buildup of an ice sheet during some glacial periods, while during others, above-freezing summer temperatures preclude a multi-year snowpack from forming.Published by Copernicus Publications on behalf of the European Geosciences Union. ried out on the supercomputer of the Norddeutscher Verbund für Hoch-und Höchstleistungsrechnen (HLRN). We thank Pedro diNezio for providing us with CESM LGM initial and boundary conditions. Financial support.

Ocean Response in Transient Simulations of the Last Deglaciation Dominated by Underlying Ice‐Sheet Reconstruction and Method of Meltwater Distribution

“…Sensitivity experiments with different model versions show that the background climate is essential for the ocean response in the simulations, as it determines how close the AMOC is to the bifurcation point between a strong and weak AMOC (Klockmann et al., 2018; Oka et al., 2012). These findings are in line with previous studies, investigating the effect of ice‐sheet boundary conditions on the atmospheric and oceanic circulation (e.g., Bakker et al., 2020; Löfverström et al., 2014; Merz et al., 2015; Pausata et al., 2011; Ullman et al., 2014) and the importance of meltwater injections for the AMOC stability (e.g., Stanford et al., 2006; Stouffer et al., 2007). Performing a first systematic ensemble of transient simulations with different ice‐sheet boundary conditions and methods of meltwater distribution, the present study extends previous studies and shows that differences in the topography and meltwater history of ICE‐6G and GLAC‐1D dominate the simulated millennial‐scale climate variability in simulations of the last deglaciation.…”

“…(2014) and Bakker et al. (2020) showed that the climate response is dependent on the ice‐sheet reconstruction used as boundary condition; small deviations in the height of the North American ice sheet between reconstructions can lead to a significantly different atmospheric and oceanic circulation. This indicates that uncertainties in the climate response are largely influenced by the glacial boundary conditions.…”

“…Past studies have investigated the model sensitivity to different ice‐sheet boundary conditions (e.g., Bakker et al., 2020; Gong et al., 2015; Hofer et al., 2012; Justino et al., 2005; Liakka & Nilsson, 2010; Liakka et al., 2016; Roe & Lindzen, 2001; Ullman et al., 2014). Using a variety of different model systems, ranging from simplified linear models of the atmosphere to complex fully coupled atmosphere‐ocean models, these studies found a strong sensitivity of the modeled climate of the last glacial maximum (LGM; about 21 ka) to the ice‐sheet topography.…”

“…A high Laurentide ice sheet leads to a zonalization and enhancement of the eddy-driven jet stream over the North Atlantic, associated with an increase in surface winds and enhanced wind-driven gyres in the North Atlantic, favoring a stronger AMOC. However, sensitivity experiments by Ullman et al (2014) and Bakker et al (2020) showed that the climate response is dependent on the ice-sheet reconstruction used as boundary condition; small deviations in the height of the North American ice sheet between reconstructions can lead to a significantly different atmospheric and oceanic circulation. This indicates that uncertainties in the climate response are largely influenced by the glacial boundary conditions.…”

Siberian environmental change: Synthesis of recent studies and opportunities for networking

“…During the Last Glacial Maximum (∼24–18 ka), ice sheets covered large parts of the Northern Hemisphere’s continents while Siberia—even its northeastern part—remained largely ice free (Bakker et al 2020 ). More recently, until the middle of the 1970s, Eurasian glaciers were in a quasi-stationary state in most of the mountain areas of the region Khromova et al 2014 ).…”