Figure 3.

Additional SLR risk to low-lying coasts and adaptation benefits over the twenty-first century. In Panel A, GMSL serves as a generic descriptor of climate change scenarios, while the risk assessment is based on end-century regional sea level rise (RSL; background SLR information on Panel B). RSL is composed of several regionally differentiated contributions (see “Projections of SLR” section and “Methods”) for each of the 13 real-world case studies used to describe the four coastal settlement archetypes (see Table 1), and mean and upper likely range values of RSL per coastal archetype are used for the risk assessment. Human-induced subsidence is not included in the RSL projections: although acknowledged to be important at several locations, especially deltas and megacities, human-induced subsidence is too difficult to project to the end of the century within reasonable uncertainty—N.B.: the assessment however does take account of abatement measures implemented in response to current rates of subsidence in scoring risk and risk reduction. Panel B shows SLR risk for the settlement archetypes today and in 2100, under RCP2.6 and RCP8.5 and under two adaptation scenarios (“None-to-moderate” vs. “High” adaptation; see “Methods” for description). Risk assessment has been conducted for each SLR and adaptation scenario, while intermediate risk levels are interpolated (see the solid and dotted burning embers’ outlines). Panel C builds on Panel B to illustrate the SLR risk reduction through local adaptation (blue, red and light brown vertical arrows for RCP2.6 median, RCP8.5 median and RCP8.5 upper likely range, respectively) and in combination with global mitigation (green arrows). It also illustrates residual risks for each SLR scenario (blue, red and light brown vertical bars). The positioning of end-century risk levels for settlement archetype precisely reflects the SROCC assessment scores (see SM2). Risk development curves are hypothetical and based on SLR projection curves (A).