"Incompletely known" is most likely an understatement!
Thus, news about sea level rise due to ice sheet loss in Greenland or Antarctica are at best alarmism and hysteria, at worst propaganda and demagoguery!
"How ice streams flow, an essential element of understanding how ice sheets lose mass, is incompletely known, making it difficult to project sea level and ice sheet size change as accurately as desired. Using measurements made with fiber-optic cables, Fichtner et al. report observations of brittle deformation in the Greenland Ice Sheet that reveal a nonviscous flow mechanism caused by englacial ice quake cascades. This effect should help to reconcile results from current ice sheet models and observations."
From the abstract:
"Ice streams are major regulators of sea level change. However, standard viscous flow simulations of their evolution have limited predictive power owing to incomplete understanding of involved processes.
On the Greenland ice sheet, borehole fiber-optic observations revealed a brittle deformation mode that is incompatible with viscous flow, over length scales similar to the resolution of modern ice sheet models: englacial ice quake cascades that are unobservable at the surface. Nucleating near volcanism-related impurities that promote grain boundary cracking, the ice quake cascades appear as a macroscopic form of crystal-scale wild plasticity. A conservative estimate indicates that seismic cascades are likely to produce strain rates that are comparable in amplitude with those measured geodetically, providing a plausible missing link between current ice sheet models and observations."
Hidden cascades of seismic ice stream deformation (open access)
Fig. 1. Experimental setting.
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