Statistically downscaled projections of the timing of the onset of annual severe bleaching (ASB) conditions under RCP8.5 for selected coral reef regions. These exemplify the high local-scale (10’s of km) variation seen in projected ASB timing in most locations and, though atypical, the low variation seen in Northern French Polynesia. Graphic: van Hooidonk, et al., 2016 / Scientific Reports

5 January 2017 (United Nations) – If current trends continue and the world fails to reduce greenhouse gas emissions, nearly all of the world's coral reefs will suffer severe bleaching – the gravest threat to one of the Earth's most important ecosystems – on annual basis, the United Nations environment agency today reported.

The finding is part of a study funded by the UN Environment Programme (UNEP) and partners, which reviewed new climate change projections to predict which corals will be affected first and at what rate. The report is published in the journal Nature Scientific Reports.

Researchers found that the reefs in Taiwan and the Turks and Caicos archipelago will be among the first to experience annual bleaching, followed by reefs off the coast of Bahrain, in Chile and in French Polynesia.

Calling the predictions “a treasure trove” for environmentalists, the head of the UN agency, Erik Solheim said the projects allow conservationists and governments to prioritize the protection reef protection.

“The projections show us where we still have time to act before it's too late,” Mr. Solheim said.

On average, the reefs will start to undergo annual bleaching starting in 2014, according to the study. Without the required minimum of five years to regenerate, the annual occurrences will have a deadly effect on the corals and disrupt the ecosystems which they support.

However, if Governments act on emission reduction pledges made in the Paris Agreement, which calls on countries to combat climate change and limit global temperature rise to below 2 degrees Celsius, the corals would have another 11 years to adapt to the warming seas.

Between 2014 and 2016, the world witnessed the longest global bleaching event recorded. Among the casualties was the Great Barrier Reef, with 90 per cent of it bleached and 20 per cent of the reef's coral killed.

Climate change will lead to annual coral bleaching, UN-supported study predicts


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 km2 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.

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

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