(How) can we attribute West Antarctic ice mass loss to climate change?

Abstract

The West Antarctic Ice Sheet is thinning and losing mass at an accelerating rate. However these changes have yet to be formally attributed to anthropogenic climate change, primarily because of the potential for positive feedbacks on ice sheet mass loss which may have been triggered even within the limits of natural internal climate variability. This begs the question: has the thinning, mass loss, and ultimately sea level rise from Antarctica resulted from anthropogenic changes? Or, is the ongoing mass loss simply the result of a positive feedback playing out on the long timescales on which ice sheets evolve? We have developed a framework to address this question, in which forcing is applied via variable ice-shelf basal melt rates with large internal variability. This framework is suitable, in particular, for use in systems with strong feedback potential. An idealised example shows that this framework permits statistically robust attribution statements to be made, even in systems that are highly susceptible to feedbacks, demonstrating the feasibility of such attribution studies for the West Antarctic Ice Sheet.