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Clim. Past, 22, 1457–1479, 2026https://doi.org/10.5194/cp-22-1457-2026© Author(s) 2026. This work is distributed underthe Creative Commons Attribution 4.0 License.The inf l uence of glacial Northern Hemisphere ice sheets onatmospheric circulationHimadri Saini 1,2,3,4 , David K. Hutchinson 1,2,5 , Josephine R. Brown 3,4 , Russell N. Drysdale 3 , Yanxuan Du 3,4 , andLaurie Menviel 1,21 Climate Change Research Centre, University of New South Wales, Sydney, New South Wales, Australia2 The Australian Centre for Excellence in Antarctic Science, University of New South Wales,Sydney, New South Wales, Australia3 School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Melbourne, Victoria, Australia4 Australian Research Council Centre of Excellence for Weather of the 21st Century, University of Melbourne,Melbourne, Victoria, Australia5 Australian Research Council Centre of Excellence for Weather of the 21st Century, University of New South Wales,Sydney, New South Wales, AustraliaCorrespondence: Himadri Saini (himadri.saini@unimelb.edu.au)Received: 28 April 2025 –Discussion started: 15 May 2025Revised: 24 June 2026 –Accepted: 3 July 2026 –Published: 5 August 2026Abstract. The Laurentide ice-sheet affected the North At-lantic Ocean during the last glacial period, but its impacton the global atmospheric circulation remains unclear. Here,we use the Australian Earth System Model to investigatethe relative roles of Marine Isotope Stage 3 (65000–25000years ago; 65–25ka) boundary conditions in shaping globalclimate ∼49ka, a period marked by prominent millennial-scale variability. Our simulations show that Northern Hemi-sphere (NH) ice sheets were the primary driver of large-scalecirculation changes. In particular, NH ice-sheet topographyinduced a 6 and 4° southward shift of the NH westerliesduring boreal winter and summer, respectively, increasingrainfall over Eurasia during summer by 31% but reducingit in winter. In contrast, orbital forcing and greenhouse gas(GHG) changes did not lead to a signif icant NH westerlyshift, while ice-sheet albedo strengthened the NH westerlies(10%–14%) through enhanced cooling (by 3–4°C) withoutaltering their position in both seasons. NH ice-sheet topog-raphy also affected the global atmospheric circulation, lead-ing to an additional 0.9° southward shift of the IntertropicalConvergence Zone (ITCZ) and a 1.5° southward displace-ment of the NH Hadley cell in austral summer, relative tochanges simulated due to orbital forcing plus GHG (0.6 and2° southward shifts for the ITCZ and the NH Hadley cell, re-spectively), and albedo (0.4 and 0.1°, respectively). The fullglacial boundary conditions, including changes in Antarcticice-sheet topography, also led to a 2° equatorward shift ofthe Southern Hemisphere (SH) Hadley cell, and a 2.5° equa-torward shift of the SH westerlies during austral winter. Or-bital forcing plus GHG and albedo primarily modulated thestrength of the SH westerlies and tropical atmospheric circu-lation. These results highlight the role of ice-sheet topogra-phy in controlling shifts in the atmospheric circulation andthe role of surface albedo in modulating atmospheric circu-lation intensity through radiative cooling.1 IntroductionEarth’s climate history has been shaped by the expansionand retreat of Northern Hemisphere (NH) ice sheets, partic-ularly during the last glacial cycle. The expansion of largeNH ice sheets has long been associated with global and re-gional cooling, particularly over the North Atlantic, whichis directly inf l uenced by the ice sheet extent and height(Kageyama et al., 2021). Ice sheet growth affects land-oceangeography by lowering sea levels (Lambeck et al., 2014), ex-posing land bridges, and altering local heating patterns dueto the differing heat capacities of land and ocean (Byrne andO’Gorman, 2013). Additionally, changes in land bridges andPublished by Copernicus Publications on behalf of the European Geosciences Union.