The uncertainty associated with the contribution to future sea-level from ice sheets remains the subject of some debate. Here we outline the nature of this uncertainty and explore its impact upon estimates of damage risk due to sea-level rise for 136 major coastal cities. We compare two sea-level projections, the process-based RCP 8.5 as calculated by IPCC and a high-end scenario that incorporates expert opinion on ice-sheet melting into RCP 8.5. By 2100, these projections differ in the global average by 10 cm and 71 cm for median and 95th percentile respectively. The probability distribution of projected sea-level for each scenario at each city and for each year is calibrated to estimate a distribution of damage risk based upon projected population and GDP combined with population distribution by elevation above present sea-level.
All cities reveal a substantial rise in damages at (Value at Risk) and above (Expected Shortfall) the 95thpercentile (i.e. low-probability high-impact coastal events). Risk is systematically higher for the larger ice-sheet contribution after 2030, while the number of cities experiencing damage of more than 200 and 20 US$ Billion by 2100 increases from 19 to 31 and 55 to 69 for RCP 8.5 and high-end scenarios respectively.
We also discuss other factors impacting local sea-level projections, such as subsidence due to ground-water extraction, and adaptation measures, which will both alter a cities vulnerability to sea-level rise, tides and storm surges.