Limits on nature-based solutions for coastal adaptation based on climate change indicators

Climate impacts increase with higher warming and evidence is mounting that impacts increase strongly above 1.5°C. Therefore, adaptation needs also rise substantially at higher warming levels. Further, limits to adaptation will be reached above 1.5°C and loss and damage will be inferred. Coastal Nature-based Solutions (NbS) have arisen as popular adaptation options, particularly for coastal developing economies and Small Island Developing States (SIDS), because of their lower overall costs compared to traditional grey infrastructure approaches such as seawalls and levees; their economic co-benefits through positive effects on sectors such as tourism and fisheries; and a broader desire to shift toward so-called blue economies. Two NbS of particular interest for coastal protection are: 1) coral reefs, which reduce coastal erosion and flooding through wave attenuation; and 2) mangroves, which provide protection from storms, tsunamis and coastal erosion. Although there is international enthusiasm to implement these solutions, there is limited understanding of the future viability of these ecosystems, particularly in their capacities as coastal adaptation service providers, in a warmer world.

In this presentation, we highlight how long and with how much coverage coral and mangrove ecosystems can provide coastal protection services for future climate scenarios, using air temperature and sea level rise as climate change indicators. A mathematical model for each ecosystem is developed, based on the physical parameters necessary for the sustainability of these ecosystems. We investigate the protective capabilities of each ecosystem under warming and sea level rise scenarios compatible with: below 1.5°C warming; below 2°C warming; warming based on current global commitments to carbon emissions reductions (3-3.5°C); and with no carbon mitigation (6°C). Results show what temperature and sea level rise values beyond which these ecosystems can no longer provide coastal protective services. These results have also been framed in a temporal window to show when these services may not be feasible, beyond which more costly adaptation measures and/or loss and damage may be incurred.