Chaotic fluctuations in Greenland ice streams limit predictability of ice sheet collapse

Abstract. The future evolution of the Greenland ice sheet (GrIS) depends on the rate and intensity of climate change and can transition to a mostly ice-free state under strong enough global warming. By applying different rates of temperature change in a state-of-the-art ice-sheet model coupled to a regional energy-moisture balance atmospheric model, oscillations in the total ice-sheet volume are found under warming magnitudes between 1.0 and 1.3 K above present-day temperatures. These oscillations are due to two ice streams located in the northern GrIS that each alternate between fast streaming and stagnation, manifesting in build-up/surge variability. These ice streams interact due to their spatial proximity, resulting in irregular periodicity. The ice streams are situated in a region where the collapse of the GrIS to an ice-free state initiates, impacting the time it takes before this transition occurs. For a fixed warming magnitude and an ensemble of warming rates and initial conditions, the timing of the collapse can differ by tens or hundreds of thousands of years. This delay is proposed to be due to a chaotic transient, suggesting that ice-stream oscillations are a potential source of internal chaotic variability in ice sheets and can complicate prospects of anticipating a collapse.