Sea Level Rise Seminar, 2021-05-04: Richard Alley

Sea Level Rise Seminar, 2021-05-04
Speaker: Richard Alley
Topic: Extraordinary results of ordinary processes: Thwaites Glacier and the risk of rapid sea-level rise

Overview: Familiar processes could lead to rapid sea-level rise if they become active in the large marine drainages of Antarctica. The grounding zone of marine-ending ice tends to stabilize in a “bottleneck” where the bed rises or the sides narrow along ice flow. Forced retreat from the bottleneck often continues to the next bottleneck upglacier, and may occur with intact ice shelves providing some buttressing or by calving from unbuttressed grounded cliffs. Retreat can be forced in many ways, but thinning or loss of ice shelves appears the most likely way for retreat to be forced in initially cold environments. Ice shelves can be removed completely by atmospheric warming leading to Larsen B-type disintegration, or by oceanic warming leading to Jakobshavn-type breakoff. Ice-shelf loss and calving-cliff retreat have been observed in the instrumental era, and reconstructed in the paleoglaciological record (Heinrich events probably represent Jakobshavn-type ice-shelf loss, for example). Ice-shelf losses triggering calving-cliff retreat during the satellite era have occurred in constrained fjords with limited ability to raise global sea level; if such events occur in a warming future in large Antarctic marine basins including West Antarctica through Thwaites Glacier, they could dominate sea-level rise. Various difficulties, however, including the extreme sensitivity of fracture to small perturbations under some conditions, make accurate modeling challenging. Models that omit ice-shelf loss or calving-cliff retreat thus project lower limits on future sea-level rise in a warming world, albeit estimates that may be accurate if ice-shelf loss and calving-cliff retreat are not triggered. Prominent published model results with ice-shelf loss and calving-cliff retreat are not worst-case scenarios. The research agenda for reducing the very large associated uncertainties is challenging, but may be advanced by greater interactions between process-based and ice-sheet-scale models informed by rapidly expanding data sets.

Видео Sea Level Rise Seminar, 2021-05-04: Richard Alley канала NASA Goddard Institute for Space Studies