Local-scale projections of coral reef futures and implications of the Paris Agreement

TLDR

Severe coral bleaching, a major climate‑change threat, varies spatially in timing and is projected by global climate models, yet coarse 1×1° resolutions and the lower‑emission RCP4.5 scenario still predict limited reef recovery before 2070. The study aimed to produce 4‑km resolution downscaled projections of annual severe bleaching for all coral reefs to capture local variation. Statistical downscaling of global climate model outputs generated 4‑km resolution projections of annual severe bleaching across all coral reefs. Timing of ASB varies >10 years in 71 of 87 countries with >500 km² reef area; RCP4.5 adds 11 years to the global average ASB timing versus RCP8.5, yet >75 % of reefs still face ASB before 2070, and reef futures vary greatly among and within countries, underscoring the need for conservation planning.

Abstract

Abstract Increasingly frequent severe coral bleaching is among the greatest threats to coral reefs posed by climate change. Global climate models (GCMs) project great spatial variation in the timing of annual severe bleaching (ASB) conditions; a point at which reefs are certain to change and recovery will be limited. However, previous model-resolution projections (~1 × 1°) are too coarse to inform conservation planning. To meet the need for higher-resolution projections, we generated statistically downscaled projections (4-km resolution) for all coral reefs; these projections reveal high local-scale variation in ASB. Timing of ASB varies >10 years in 71 of the 87 countries and territories with > 500 km 2 of reef area. Emissions scenario RCP4.5 represents lower emissions mid-century than will eventuate if pledges made following the 2015 Paris Climate Change Conference (COP21) become reality. These pledges do little to provide reefs with more time to adapt and acclimate prior to severe bleaching conditions occurring annually. RCP4.5 adds 11 years to the global average ASB timing when compared to RCP8.5; however, >75% of reefs still experience ASB before 2070 under RCP4.5. Coral reef futures clearly vary greatly among and within countries, indicating the projections warrant consideration in most reef areas during conservation and management planning.