Ice streams and ice sheet sensitivity

Ice streams can display oscillatory and even chaotic behaviour. Does the internal state of an ice stream affect how the ice sheet responds to anthropogenic warming? And if so, how predictable is future sea level rise?

Ice streams can surge and stagnate on their own, without any change in climate. If the response of an ice sheet to warming depends on where an ice stream is in its cycle when the warming starts, then the same forcing could give different amounts of sea level rise. Any such spread would be an irreducible uncertainty, and would fundamentally limit our ability to make sea level projections.

In this project you will set up an ice sheet with an oscillating ice stream, possibly with an idealized geometry, and force it with warming scenarios starting from different phases of the oscillation. You will then investigate how the transient sea level sensitivity varies with the ice stream state.

There is flexibility in how to approach this. It can be explored using conceptual models such as Robel’s zero-dimensional ice stream oscillator, or with a full ice sheet model such as PISM, or a combination where the conceptual model guides the setup of the full model.

Builds on:

• The transient sensitivity of sea level rise (Grinsted and Christensen, 2021)
• Kolja Leon Kypke’s PhD thesis
• Existing sea level data and models

Ice stream oscillations:

• MacAyeal (1993): the classic binge/purge oscillation model
• Robel et al. (2013): a zero-dimensional model of ice stream variability
• Feldmann and Levermann (2017): cyclic ice streaming in PISM with an idealized geometry

Predictability and uncertainty:

• Robel, Seroussi and Roe (2019): how ice sheet instability amplifies and skews uncertainty in sea level projections