Marine-terminating glaciers in Greenland and Antarctica are currently retreating and thinning. In this talk, I describe a simple dynamical model which accurately emulates the response of marine-terminating glaciers to external forcing simulated in more realistic models. I explain and use the fluctuation-dissipation theorem to understand the transient glacier response to external forcing. This analysis shows that there is a fast time scale of decades to centuries and a slow time scale of millennia that characterize both stationary glacier fluctuations and the non-stationary glacier response to climate forcing on prograde bed slopes. The two time scales are also associated with two different forms of the marine ice sheet instability due to different physical mechanisms. The slow marine ice sheet instability occurs at nearly flat bed slopes and evolves on time scales of hundreds to thousands of years. The fast marine ice sheet instability only occurs on steep retrograde slopes and causes rapid retreat on decadal time scales, similar to what is observed at some glaciers in Greenland and West Antarctica. The sensitivity of glacier thickness and grounding-line position to external forcing depends on the equilibrium glacier state, bed slope and the type of forcing process, in line with recent studies that find a spatially-varying sensitivity of glacier thickness to forcing. The slow marine-terminating glacier response to forcing indicates that current glacier change on prograde bed slopes is likely to continue and accelerate in coming centuries regardless of future climate forcing. I also show that the spread and fat-tail of uncertainty in stochastic ensemble projections of future ice sheet change can be amplified by the marine ice sheet instability. I conclude by discussing how we can interpret observations of marine-terminating glacier change in light of these results and novel ensemble techniques for robustly simulating future ice sheet change.
Watch Live: http://bit.ly/2vBaYD0
Learn about Alex Robel: https://sites.google.com/site/alexanderrobel/
UTIG Host: Ginny Catania
When: Fri Sep 1, 2017 10:30am 11:30am Central Time