High-End Scenarios of Sea-Level Rise for Coastal Risk-Averse Stakeholders

Abstract

Sea-level rise (SLR) will be one of the major climate change-induced risks of the 21st century for coastal areas. The large uncertainties of ice sheet melting processes bring in a range of unlikely – but not impossible – high-end sea-level scenarios (HESs). Here, we provide global to regional HESs exploring the tails of the distribution estimates of the different components of sea level. We base our scenarios on high-end physical-based model projections for glaciers, ocean sterodynamic effects, glacial isostatic adjustment and contributions from land-water, and we rely on a recent expert elicitation assessment for Greenland and Antarctic ice-sheets. We consider two future emissions scenarios and three time horizons that are critical for risk-averse stakeholders (2050, 2100, and 2200). We present our results from global to regional scales and highlight HESs spatial divergence and their departure from global HESs through twelve coastal city and island examples. For HESs-A, the global mean-sea level (GMSL) is projected to reach 1.06(1.91) in the low(high) emission scenario by 2100. For HESs-B, GMSL may be higher than 1.69(3.22) m by 2100. As far as 2050, while in most regions SLR may be of the same order of magnitude as GMSL, at local scale where ice-sheets existed during the Last Glacial Maximum, SLR can be far lower than GMSL, as in the Gulf of Finland. Beyond 2050, as sea-level continue to rise under the HESs, in most regions increasing rates of minimum(maximum) HESs are projected at high(low-to-mid) latitudes, close to (far from) ice-sheets, resulting in regional HESs substantially lower(higher) than GMSL. In regions where HESs may be extremely high, some cities in South East Asia such as Manila are even more immediately affected by coastal subsidence, which causes relative sea-level changes that exceed our HESs by one order of magnitude in some sectors.

Investigations Exploring the Use of an Unstructured-Grid, Finite-Volume Modelling Approach to Simulate Coastal Circulation in Remote Island Settings—Case Study Region, Vanuatu/New Caledonia

“…From this analysis, if temperatures stabilised at 2 • C above pre-industrial levels by 2100, HESs in the Vanuatu/New Caledonia region was estimated to increase by between 1 and 1.2 m, under the "likely" (17-83%) range, increasing to 1.8-2 m under the "credible" (5-95%) range. If temperatures stabilised at 5 • C over this same period HES increased to 2-2.2 m and 3.5-3.8 m under the "likely" and "credible" ranges respectively (Dayan et al, 2021).…”

“…Similar analysis of ensemble CMIP6 data estimating regional SLR are presently not available, however, it is anticipated that similar variations of up to 10% from global values might be expected. In an effort to provide useful information for risk averse stakeholders, such as coastal planners and managers of critical infrastructure, Dayan et al (2021) conducted an assessment of high-end sea level scenarios (HESs), providing maps of regional HESs projections. From this analysis, if temperatures stabilised at 2 • C above pre-industrial levels by 2100, HESs in the Vanuatu/New Caledonia region was estimated to increase by between 1 and 1.2 m, under the "likely" (17-83%) range, increasing to 1.8-2 m under the "credible" (5-95%) range.…”

“…It is recognised that this value likely does not fully account for contributions associated with the instability of the Antarctic ice sheet due to the assumptions made when generating the CMIP6 ensemble estimates (Hermans et al, 2021). The 2 m SLR value employed, reflects "credible" high-end scenarios of SLR by 2100, assuming 2 • C warming relative to pre-industrial air temperatures, while also falling within the "likely" range assuming 5 • C warming (Dayan et al, 2021), where high-end scenario values attempt to better account for the contribution of the Antarctic ice sheet. SLR values of 1 and 2 m were also chosen in this study to be consistent with other studies addressing the impact of SLR (e.g., Pelling and Green, 2013;Pickering et al, 2017).…”

The evolution of UK sea-level projections

“…Little et al 2019) and a shutdown could affect extreme sea level through changes in storminess in Europe (Jackson et al 2015). Through collaboration, storylines could be created which best fit information requirements or summarised as a matrix of possibilities for downstream users to explore, depending on their risk tolerance and information required ( van Vuuren et al 2014, Stammer et al 2019, Dayan et al 2021. As part of adaptive planning or dynamic decision-making, it is essential to monitor the real-world sea-level trajectory to monitor GMSL, LMSL and component sea-level change (e.g.…”

Analysis of the Evolution of Parametric Drivers of High-End Sea-Level Hazards

“…To understand the impact on near-term and longterm risks, it is important to consider how the contribution of each parametric uncertainty to overall high-end sea-level hazard changes over time. Understanding how these uncertainties change over time will aid in risk-averse decision-making related to adaptation to sea-level rise (Dayan et al, 2021).…”