Risks to future atoll habitability from climate‐driven environmental changes

Abstract

Recent assessments of future risk to atoll habitability have focused on island erosion and submergence, and have overlooked the effects of other climate‐related drivers, as well as differences between ocean basins and island types. Here we investigate the cumulative risk arising from multiple drivers (sea‐level rise; changes in rainfall, ocean–atmosphere oscillations and tropical cyclone intensity; ocean warming and acidification) to five Habitability Pillars: Land, Freshwater supply, Food supply, Settlements and infrastructure, and Economic activities. Risk is assessed for urban and rural islands of the Pacific and Indian Oceans, under RCP2.6 and RCP8.5, in 2050 and 2090, and considering a moderate adaptation scenario. Risks will be highest in the Western Pacific which will experience increased island destabilization together with a high threat to freshwater, and decreased land‐based and marine food supply from reef‐dependent fish and tuna and tuna‐like resources. Risk accumulation will occur at a lower rate in the Central Pacific (lower pressure on land, with more limited cascading effects on other Habitability Pillars; increase in pelagic fish stocks) and the Central Indian Ocean (mostly experiencing increased land destabilization and reef degradation). Risk levels will vary significantly between urban islands, depending on geomorphology and local shoreline disturbances. Rural islands will experience less contrasting risk levels, but higher risks than urban islands in the second half of the century. This article is categorized under: Trans‐Disciplinary Perspectives > Regional Reviews

Coastal flooding and mean sea-level rise allowances in atoll island

“…Furthermore humans living on atoll islands are adapting these islands either by artificial infrastructures (breakwaters, dikes, etc. ), elevating buildings and raising whole islands 2 , 11 – 13 , or by reinstalling ecosystem services such as the natural capacity of islands to accrete vertically with mean sea-level rise 2 , 14 , 15 provided sufficient sediment is available and the time span is long enough 16 .…”

Internal relocation as a relevant and feasible adaptation strategy in Rangiroa Atoll, French Polynesia

“…Another main advantage of settling and developing the latter two islands is that they would not flood over their entire surface during intense cyclonic events in 2100, even under SSP5-8.5. In the case of Rangiroa and other atolls located in regions where TCs are rare, high-tide chronic flooding represents, from a climate perspective, the highest risk faced under climate change as it would affect land availability, which represents the central pillar for atoll island habitability 6 . Based on the lessons learnt from the most intense TCs that have already affected the atoll 47 , 48 , 54 , we assume that the disruption caused by extensive cyclone-induced flooding and wind-driven destruction would probably not lead to the permanent depopulation of the atoll in the future.…”

“…Flooding already has adverse consequences on freshwater availability, subsistence and commercial activities, infrastructure and buildings in atoll islands 4 , 5 . Further increases in flood frequency, intensity, and spatial extent, as well as the decline of the reef ecosystem, will likely render some atoll islands uninhabitable from the mid-century 6 , 7 .…”

“…This is, first, because in atoll islands ‘ the room to move back is very limited’ ( 20 : 134), and second, because atoll islands are generally considered to be all equally (that is, highly) susceptible to flooding 7 . Yet, insights from geomorphic studies show that some atoll islands are less flood- and risk-prone than others 6 , 8 , 21 – 23 . Internal relocation refers to ‘ the long-term [at least for several decades] movement of a community from one threatened area [or island] to a less risk-prone area [or island], in which the societal structures, legal and political systems, cultural characteristics and worldviews of this community are retained’ ( 24 : 58–59).…”

The existential risk space of climate change

“…The consideration of protection from hazards which challenge human survival alludes to lifethreatening aspects, while the assurance of space, food, and freshwater refers more to the notion of basic needs. Building on these ideas, Duvat et al (2021) use a concept of habitability pillars for atoll islands, in which they include a component of access to sustainable economic activities. However, the most basic existential aspect of habitability is that of survival at a specific location, threatened, e.g., by sea-level rise, floods, and storm surges or excess heat.…”