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WIREs Clim Change
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Risks to future atoll habitability from climate‐driven environmental changes

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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
Conceptual model of atoll island habitability. The atoll island system comprises five pillars supported by ecosystems and societal conditions. Interactions between these pillars are illustrated by blue arrows: For example, habitable land is critical to settlements and infrastructure, freshwater and food supply, economic activities, and natural vegetation development; in turn, the persistence of land is dependent on supporting ecosystems; thus the reef ecosystem provides the island with sediment and reduces wave energy reaching the coastline. Similarly, mangrove, seagrass, and the natural strandline vegetation stabilize shoreline systems and can limit erosion and marine flooding
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Aggregated additional climate risk to habitability for four atoll islands in the central Indian and Western Pacific oceans. See especially SM8 for details on the method
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Additional climate risks to the five habitability pillars for four atoll islands in the central Indian and Western Pacific oceans. “Additional” means additional risk to habitability compared to a present‐day baseline. See Part II of the Supplementary Material for details on the assessment method and results
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Cumulative climate change threats and related exposure of atoll regions, for two emission scenarios in 2050 and 2090, based on mean projected rates of change. SM3.1 provides the full details. Panel a illustrates the cumulative climate and climate‐related ocean threats (high = 1.0, low = 0.0) to atoll habitability for each of the three delineated atoll regions. Panel b shows resultant cumulative exposure index for each RCP scenario and atoll region. The index is described in SM3.2. The color graduation represents increasing exposure levels from low (white to light blue) to high (deep blue)
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Projected changes in relevant climate change‐driven ocean and atmospheric parameters within different atoll regions for each emissions scenario in 2050 and 2090. Plots a–e show upper, mean and lower limit projected changes in each parameter under RCP2.6 and RCP8.5 in 2050 and 2090 for each atoll subregion (see also SM3.1). The threshold levels (gray bars) denote the following: for sea level trend, the mean rate of global sea‐level rise (3.6 mm year−1) between 2006 and 2015 (IPCC, 2019); for SST trends, regional bleaching thresholds (from NOAA Coral Reef Watch, 2001–2020 time series data); for Aragonite Saturation State trends, the threshold below which conditions for tropical reef‐building corals are deemed to be “extremely marginal” (Guinotte et al., 2003); for surface pH, the mean surface pH in tropical regions during the period 1980–2000 (IPCC, 2014, fig. 30.7)
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Assessment protocol used in this study. See SM4 for further details
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