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Global warming: Study maps coral reef vulnerability

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Global warming threatens coral reef diversity. Photo courtesy NOAA.

74 percent of world’s reefs could see annual bleaching events by 2035

By Summit Voice

FRISCO — Using the latest data from the upcoming IPCC climate assessment, ocean researchers have concluded that about three-quarters of the world’s coral reefs could face annual bleaching events in just a short 30 years, and they’ve mapped out which areas will be hit first.

“This study represents the most up-to-date understanding of spatial variability in the effects of rising temperatures on coral reefs on a global scale,” said researcher Serge Planes, Ph.D., from the French research institute CRIOBE in French Polynesia.

Large-scale bleaching events on coral reefs are caused by higher-than-normal sea temperatures. High temperatures make light toxic to the algae that reside within the corals. The algae, called ‘zooxanthellae’, provide food and give corals their bright colors. When the algae are expelled or retained but in low densities, the corals can starve and eventually die. Bleaching events caused a reported 16 percent loss of the world’s coral reefs in 1998 according to the Global Coral Reef Monitoring Network.

The findings show that, without significant reductions in emissions, most coral reefs are at risk. Reducing carbon emissions would delay annual bleaching events more than two decades in nearly a quarter (23 percent) of the world’s reef areas, the research shows.

About a quarter of coral reefs are likely to experience bleaching events annually five or more years earlier than the median year, and these reefs in northwestern Australia, Papau New Guinea, and some equatorial Pacific islands like Tokelau, may require urgent attention, the researchers warned.

“Coral reefs in parts of the western Indian Ocean, French Polynesia and the southern Great Barrier Reef, have been identified as temporary refugia from rising sea surface temperatures,” said Ruben van Hooidonk, Ph.D., from the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami and NOAA’s Atlantic Oceanographic and Meteorological Laboratory. “These locations are not projected to experience bleaching events annually until five or more years later than the median year of 2040, with one reef location in the Austral Islands of French Polynesia protected from the onset of annual coral bleaching conditions until 2056.”

“Our projections indicate that nearly all coral reef locations would experience annual bleaching later than 2040 under scenarios with lower greenhouse gas emissions.” said Jeffrey Maynard, Ph.D., from the Centre de Recherches Insulaires et Observatoire de l’Environnement (CRIOBE) in Moorea, French Polynesia. “For 394 reef locations (of 1707 used in the study) this amounts to at least two more decades in which some reefs might conceivably be able to improve their capacity to adapt to the projected changes.”

“More so than any result to date, this highlights and quantifies the potential benefits for reefs of reducing emissions in terms of reduced exposure to stressful reef temperatures.”

The study was published this week in Nature Climate Change.

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