Is climate change responsible for recent retreat of the Pine Island Glacier in West Antarctica?

Pine Island Glacier is a fast flowing ice stream in West Antarctica. At present, it is rapidly thinning and retreating, and has been since at least the 1970s, when satellite records began. Sediment records indicate that this retreat was initiated in the 1940s, but the influence of climate change on key forcing components only became significant in the 1960s, i.e. the trigger for retreat occurred naturally. However, current ice loss remains responsive to fluctuations in forcing, indicating that Pine Island Glacier is not undergoing a purely unstable retreat after this trigger. This begs the question: to what extent is climate change responsible for the recent retreat of the Pine Island Glacier?

Adopting a recently published framework, we assess this question. One major challenge is the computational expense associated with the large ensemble of simulations required to account for significant uncertainties in ice sheet model parameters; to overcome this, we use a two stage Ensemble Kalman Inversion and Model Emulation approach. Ultimately, this procedure yields posterior distributions of parameters, including the trend in forcing resulting from climate change; essentially, this allows us to address the question: given the observed Pine Island Glacier retreat, how large does the trend in forcing have to have been?