Glacial inception through rapid ice area increase driven by albedo and vegetation feedbacks

Abstract

Abstract. We present transient simulations of the last glacial inception using the Earth system model CLIMBER-X with dynamic vegetation, interactive ice sheets and visco-elastic solid-Earth response. The simulations are initialized at the middle of the Eemian interglacial (125 kiloyears before present, ka) and run until 100 ka, driven by prescribed changes in Earth’s orbital parameters and greenhouse gas concentrations from ice core data. CLIMBER-X simulates a rapid increase in Northern Hemisphere ice sheet area through MIS5d, with ice sheets expanding over northern North America and Scandinavia, in broad agreement with proxy reconstructions. While most of the increase in ice sheet area occurs over a relatively short period between 119 ka and 117 ka, the larger part of the increase in ice volume occurs afterwards with an almost constant ice sheet extent. We show that the vegetation feedback plays a fundamental role in controlling the ice sheet expansion during the last glacial inception. In particular, with prescribed present-day vegetation the model simulates a global sea level drop of only ∼20 m, compared with the ∼35 m decrease in sea level with dynamic vegetation response. The ice sheet and carbon-cycle feedbacks play only a minor role during the ice sheet expansion phase prior to ∼115 ka, but are important in limiting the deglaciation during the following phase characterized by increasing summer insolation. The model results are sensitive to climate model biases and to the parameterisation of snow albedo, while they show only a weak dependence on changes in the ice sheet model resolution and the acceleration factor used to speed up the climate component. Overall, our simulations confirm and refine previous results showing that climate-vegetation-cryosphere-carbon cycle feedbacks play a fundamental role in the transition from interglacial to glacial states characterising Quaternary glacial cycles.

New estimation of critical insolation – CO2 relationship for triggering glacial inception

“…We employ the new CLIMBER-X EMIC (Willeit et al, 2022(Willeit et al, , 2023a(Willeit et al, , 2023b. The model was specifically designed to simulate the Earth system evolution on timescales from decades to hundreds of thousands of years.…”

“…The viscoelastic solid Earth model VILMA (Klemann et al, 2008;Martinec et al, 2018) is used to simulate the bedrock response to changes in loading by solving the sea-level equation. A detailed description of the coupling between climate and ice sheet components is provided in Willeit et al (2023b).…”

“…Preliminary experiments show that such biases preclude the realistic development of North American ice-sheets. Therefore, similarly to Ganopolski et al (2010), we implement a 2m-temperature bias correction in the surface mass balance calculation (see Willeit et al, 2023b). In addition, a uniform offset of -0.5°C is applied globally in the surface mass balance scheme.…”

“…The purpose of this work is to build upon the findings of Ganopolski et al (2016) and generate a new estimation of the relationship between insolation and atmospheric CO2 critical for triggering glacial inception, using the recently developed and more advanced CLIMBER-X model (Willeit et al, 2022(Willeit et al, , 2023a(Willeit et al, , 2023b. While CLIMBER-X is also an EMIC that shares with https://doi.org/10.5194/cp-2023-81 Preprint.…”

New estimation of critical insolation–CO2 relationship for triggering glacial inception

“…The purpose of this work is to build upon the findings of Ganopolski et al (2016) and generate a new estimation of the relationship between insolation and atmospheric CO 2 critical for triggering glacial inception using the recently developed and more advanced CLIMBER-X model (Willeit et al, 2022(Willeit et al, , 2023(Willeit et al, , 2024. While CLIMBER-X is also an EMIC that shares with CLIMBER-2 the principles of computational efficiency and usage of a statistical-dynamical atmospheric model, it represents a significant development compared to the CLIMBER-2 model used in previous studies (Ganopolski and Brovkin, 2017;Willeit et al, 2019).…”