Exploring ice sheet model sensitivity to ocean thermal forcing using the Community Ice Sheet Model (CISM)

• Main Authors: Berdahl, Mira, Leguy, Gunter, Lipscomb, William H., Urban, Nathan M., Hoffman, Matthew J.
• Format: Text
• Language: English
• Published: 2022
• Subjects: Antarctic; The Antarctic; Antarc*; Ice Sheet; Ice Shelf
• Online Access: https://doi.org/10.5194/tc-2022-156; https://tc.copernicus.org/preprints/tc-2022-156/

Multi-meter sea level rise (SLR) is thought to be possible within a century or two, with most of the uncertainty originating from the Antarctic land ice contribution. One source of uncertainty relates to the ice sheet model initialization. Since ice sheets have a long response time (compared to other Earth system components such as the atmosphere), ice sheet model initialization methods can have significant impacts on how the ice sheet responds to future forcings. To assess this, we generated 25 different ice sheet spin-ups, using the Community Ice Sheet Model (CISM) at 4 km resolution. During each spin-up we varied two key parameters known to impact the sensitivity of the ice sheet to future forcing: One related to the sensitivity of the ice-shelf melt rate to ocean thermal forcing, and the other related to the basal friction. The spin-ups all nudge toward observed thickness and enforce a no-advance calving criterion, such that all final spun-up states resemble observations but differ in their melt and friction parameter settings. Each spin-up was then forced with future ocean thermal forcings from 13 different CMIP6 models under the SSP5-8.5 emissions scenario, and modern climatological surface mass balance data. Our results show that the effects of the ice sheet and ocean parameter settings used during the spin-up are capable of impacting multi-century future SLR predictions by as much as 2 m. By the end of this century, the effects of these choices are more modest, but still significant, with differences of up to 0.2 m of SLR. We have identified a combined ocean and ice parameter space that leads to widespread mass loss (low friction & high melt rate sensitivity). To explore temperature thresholds, we also ran a synthetically-forced CISM ensemble that is focused on the Amundsen region only. We find that given certain ocean and ice parameter choices, Amundsen mass loss can be triggered with thermal forcing anomalies between 1.5 and 2 °C. Our results emphasize the critical importance of considering ice ...