Probabilistic Projections of Future Sea-Level Change and Their Implications for Flood Risk Management: Insights from the American Climate Prospectus

Robert E Kopp1, Michael Delgado2, Radley M Horton3, Trevor Houser2, Christopher M Little4, Robert Muir-Wood5, Michael Oppenheimer6, DJ Rasmussen7, Benjamin Strauss8 and Claudia Tebaldi9, (1)Rutgers University New Brunswick, Department of Earth and Planetary Sciences, New Brunswick, NJ, United States, (2)Rhodium Group, Oakland, United States, (3)Columbia University/NASA GISS, New York, NY, United States, (4)JANUS Research Group, Lexington, United States, (5)Risk Management Solutions, Inc., Newark, CA, United States, (6)Princeton University, School of Public and International Affairs, Princeton, NJ, United States, (7)Rhodium Group, Oakland, CA, United States, (8)Climate Central, Princeton, NJ, United States, (9)Pacific Northwest National Laboratory, Joint Global Change Research Institute, College Park, United States
Abstract:
Global mean sea level (GMSL) rise projections are insufficient for adaptation planning; local decisions require local projections that characterize risk over a range of timeframes and tolerances. We present a global set of local sea level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We present complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling [1]. We illustrate the application of this framework by estimating the joint distribution of future sea-level change and coastal flooding, and associated economic costs [1,2].

In much of the world in the current century, differences in median LSL projections are due primarily to varying levels of non-climatic uplift or subsidence. In the 22nd century and in the high-end tails, larger ice sheet contributions, particularly from the Antarctic ice sheet (AIS), contribute significantly to site-to-site differences. Uncertainty in GMSL and most LSL projections is dominated by the uncertain AIS component.

Sea-level rise dramatically reshapes flood risk. For example, at the New York City (Battery) tide gauge, our projections indicate a \emph{likely} (67% probability) 21st century LSL rise under RCP 8.5 of 65--129 cm (1-in-20 chance of exceeding 154 cm). Convolving the distribution of projected sea-level rise with the extreme value distribution of flood return periods indicates that this rise will cause the current 1.80 m `1-in-100 year' flood event to occur an expected nine times over the 21st century -- equivalent to the expected number of `1-in-11 year' floods in the absence of sea-level change.

Projected sea-level rise for 2100 under RCP 8.5 would likely place $80-$160 billion of current property in New York below the high tide line, with a 1-in-20 chance of losses >$190 billion. Even without accounting for potential changes in storms themselves, it would likely increase average annual storm damage by $2.6-$5.2 billion (1-in-20 chance of >$7 billion). Projected increases in tropical cyclone intensity would further increase damages [2].

References: [1] R. E. Kopp et al. (2014), Earth's Future, doi:10.1002/2014EF000239. [2] T. Houser et al. (2014), American Climate Prospectus, www.climateprospectus.org.

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