  Future sea-level rise drives severe risks for many coastal communities.
Strategies to manage these risks hinge on a sound characterization of the
uncertainties. For example, recent studies suggest that large fractions of the
Antarctic ice sheet (AIS) may rapidly disintegrate in response to rising global
temperatures, leading to potentially several meters of sea-level rise during
the next few centuries. It is deeply uncertain, for example, whether such an
AIS disintegration will be triggered, how much this would increase sea-level
rise, whether extreme storm surges intensify in a warming climate, or which
emissions pathway future societies will choose. Here, we assess the impacts of
these deep uncertainties on projected flooding probabilities for a levee ring
in New Orleans, Louisiana. We use 18 scenarios, presenting probabilistic
projections within each one, to sample key deeply uncertain future projections
of sea-level rise, radiative forcing pathways, storm surge characterization,
and contributions from rapid AIS mass loss. The implications of these deep
uncertainties for projected flood risk are thus characterized by a set of 18
probability distribution functions. We use a global sensitivity analysis to
assess which mechanisms contribute to uncertainty in projected flood risk over
the course of a 50-year design life. In line with previous work, we find that
the uncertain storm surge drives the most substantial risk, followed by general
AIS dynamics, in our simple model for future flood risk for New Orleans.
