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 (approximately 1x1°) are too coarse to inform reef management planning (recognized, for example, in SAMOA Pathways, paragraph 44b).
To meet the need for higher-resolution projections, the first objective of this report is to present statistically downscaled projections (4-km resolution) for all the world’s coral reefs using the newest generation of IPCC climate models (CMIP5). Results are reported by country and territory, grouped in bioregions based on the 10 UNEP Regional Seas programmes with coral reefs (also including countries or territories in or near the Regional Sea area but not participating in the Regional Sea). Among the goals of the Paris Agreement adopted at the UNFCCC Conference of Parties (COP) in 2015 is to hold temperature “well below” 2°C while also pursuing efforts to stay below 1.5°C. This legally binding agreement entered into force 4 November 2016.
The second objective of this report is to evaluate the implications of the Paris Agreement for coral reef futures by comparing projections of ASB timing between successful mitigation in line with or exceeding the 1.5 °C ‘aspiration (i.e. greenhouse gas concentration trajectory RCP4.5) and a business as usual scenario (RCP8.5).
The third objective of this report is to make the projection data and main findings publicly accessible to inform management and policy planning as well as to support education and outreach.
