Abstract
This manuscript discusses the challenges in detecting and attributing
recently observed trends in the Atlantic hurricanes and the epistemic
uncertainty we face in assessing future hurricane risk. Data used here
include synthetic storms downscaled from five CMIP5 models by the
Columbia HAZard model (CHAZ), and directly simulated storms from
high-resolution climate models. We examine three aspects of recent
hurricane activity: the upward trend and multi-decadal oscillation of
the annual frequency, the increase in storm wind intensity, and the
downward trend in the forward speed. Some datasets suggest that these
trends and oscillation are forced while others suggest that they can be
explained by natural variability. Future projections under warming
climate scenarios also show a wide range of possibilities, especially
for the annual frequencies, which increase or decrease depending on the
choice of moisture variable used in the CHAZ model and on the choice of
climate model. The uncertainties in the annual frequency lead to
epistemic uncertainties in the future hurricane risk assessment. Here,
we investigate the reduction of epistemic uncertainties on annual
frequency through a statistical practice – likelihood analysis. We find
that historical observations are more consistent with the simulations
with increasing frequency but we are not able to rule out other
possibilities. We argue that the most rational way to treat epistemic
uncertainty is to consider all outcomes contained in the results. In the
context of hurricane risk assessment, since the results contain possible
outcomes in which hurricane risk is increasing, this view implies that
the risk is increasing.