Impacts of Antarctic fast dynamics on sea-level projections and coastal flood defense

Abstract

Strategies to manage the risks posed by future sea-level rise hinge on a sound characterization of the inherent uncertainties. One of the major uncertainties is the possible rapid disintegration of large fractions of the Antarctic ice sheet in response to rising global temperatures. This could potentially lead to several meters of sea-level rise during the next few centuries. Previous studies have typically been silent on two coupled questions: (i) What are probabilistic estimates of this "fast dynamics" contribution to sea-level rise? (ii) What are the implications for strategies to manage coastal flooding risks? Here, we present probabilistic hindcasts and projections of sea-level rise to 2100. The fast dynamics mechanism is approximated by a simple parameterization, designed to allow for a careful quantification of the uncertainty in its contribution to sea-level rise. We estimate that global temperature increases ranging from 1.9 to 3.1°C coincide with fast Antarctic disintegration, and these contributions account for sea-level rise of 21-74 centimeters this century (5-95% range, Representative Concentration Pathway 8.5). We use a simple cost-benefit analysis of coastal defense to demonstrate in a didactic exercise how neglecting this mechanism and associated uncertainty can (i) lead to strategies which fall sizably short of protection targets and (ii) increase the expected net costs.

Sea Level Change and Coastal Climate Services: The Way Forward

“…This raises the need for other theories of uncertainties able to convey differences among different estimates while minimizing the introduction of arbitrary information in uncertainty representations [153,154]. These latter approaches are complementary to probabilistic descriptions of uncertainties: in some coastal areas, users will require an optimal response to SLR through probabilistic projections [89,155], whereas others will use sea level scenarios or projections conveying minimum or maximum SLR estimates, in order to estimate minimum adaptation needs or to explore high end scenarios 1 .…”

Epistemic and ethical trade-offs in decision analytical modelling

“…Of the 354,000 people (approximately three quarters of the population) who lived in heavily flooded areas of the New Orleans, 29% were living in poverty (Gabe et al 2005;Logan 2006;Sharkey 2007). The death rate among people older than 65 was 15 times higher than that of those younger 65 (Sharkey 2007;Walker 2012). This paper focuses on two decision analytical models that inform Louisiana's Coastal Protection and Restoration Authority (CPRA).…”

“…Based on the pioneering study of David van Dantzig (1956), DPM is an economic optimization model that compares the investment costs of levee heightening with expected losses due to flooding. Apart from its short run time, its simplicity and transparent setup allow for the incorporation of additional considerations beyond the parameters of the original model, such as the effect of accelerated sea-level change (Wong et al 2017a).…”

Deep Uncertainty Surrounding Coastal Flood Risk Projections: A Case Study for New Orleans

“…The United States Army Corps of Engineers (USACE) has stated its objective to develop coastal defense strategies (including for New Orleans) that perform well across a range of plausible climate change scenarios (Moritz et al, 2015). However, recent scientific findings suggest that future flood risks may be higher and more uncertain than previously estimated (e.g., Grinsted et al, 2013;DeConto & Pollard, 2016;Abadie et al, 2017;Bakker et al, 2017;Wong et al, 2017a). Here, we assess the expected performance of the flood protection system in New Orleans under a set of plausible future climate scenarios that account for key new scientific findings and sample key deep uncertainties.…”

“…Previous approaches to project future storm surges have included physical modeling (e.g., Orton et al, 2016), statistical modeling (e.g., Grinsted et al, 2013), and scenarios (e.g., Lempert et al, 2012;Johnson et al, 2013). Potential fast Antarctic ice sheet (AIS) disintegration via cliff instability and hydrofracturing in response to rising global temperatures is a critical deep uncertainty, driving potentially large changes in sea-level rise this century (DeConto & Pollard, 2016;Oppenheimer & Alley, 2016;Bakker et al, 2017;Ruckert et al, 2017;Wong et al, 2017a). Potential fast Antarctic ice sheet (AIS) disintegration via cliff instability and hydrofracturing in response to rising global temperatures is a critical deep uncertainty, driving potentially large changes in sea-level rise this century (DeConto & Pollard, 2016;Oppenheimer & Alley, 2016;Bakker et al, 2017;Ruckert et al, 2017;Wong et al, 2017a).…”