  The response of the Antarctic ice sheet (AIS) to changing climate forcings is
an important driver of sea-level changes. Anthropogenic climate change may
drive a sizeable AIS tipping point response with subsequent increases in
coastal flooding risks. Many studies analyzing flood risks use simple models to
project the future responses of AIS and its sea-level contributions. These
analyses have provided important new insights, but they are often silent on the
effects of potentially important processes such as Marine Ice Sheet Instability
(MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well
justified and result in more parsimonious and transparent model structures.
This raises the question of how this approximation impacts hindcasts and
projections. Here, we calibrate a previously published and relatively simple
AIS model, which neglects the effects of MICI and regional characteristics,
using a combination of observational constraints and a Bayesian inversion
method. Specifically, we approximate the effects of missing MICI by comparing
our results to those from expert assessments with more realistic models and
quantify the bias during the last interglacial when MICI may have been
triggered. Our results suggest that the model can approximate the process of
MISI and reproduce the projected median melt from some previous expert
assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the
observed data during the last interglacial period and our mean projection is
roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year
2100. These results suggest that missing MICI and/or regional characteristics
can lead to a low-bias during warming period AIS melting and hence a potential
low-bias in projected sea levels and flood risks.
