The risks to coral reefs are accelerating largely due to human activity, with rising water temperatures meaning they now have about 80 percent less recovery time between bleaching episodes than just three decades ago, according to a report in the journal Science.
In a study of 100 reefs around the world, the report found coral will have a bleaching event every six years, from every 27 years in the 1980s, when mass bleaching events began to be observed. With the likelihood of human activity causing further increases in sea temperature, reefs may bleach every hot summer in coming decades, the report said.
“Scientists have been saying for 30 to 40 years now that annual bleaching events could be a possibility unless we address climate change, so it’s a little bit disappointing,” study co-author Andrew Baird told Australian Broadcasting Corp.’s Radio National program. “Human folly is an extraordinary thing.”
Coral reefs are being damaged at increasing rates and even currently safe pockets are at risk of destruction by the middle of this century, the report said, citing an earlier study.
Bleaching is a problem because, while it doesn’t immediately cause death, it puts coral at much greater risk of dying. A coral bleaches when it expels the algae it depends on to survive due to stress induced by factors such as rising water temperatures. Without the algae, which also provide the coral with their bright coloring, coral turns a ghostly white and starts to starve. Coral generally needs 10 to 15 years to recover fully between bleaching, the report said.
A “1.5 or 2 degrees Celsius warming above pre-industrial conditions will inevitably contribute to further degradation of the world’s reefs,” the report said.
The study by 25 researchers, led by Terry Hughes from the Australian Research Council Centre of Excellence for Coral Reef Studies, found 31 percent of reefs examined were at risk of bleaching in 2016 compared with just 4 percent in the 1980s.
In the past, coral bleaching occurred when warmer winds and El Nino weather conditions heated up sea surfaces. Now, reefs are bleaching even in the absence of these winds, as global warming pushes up temperatures without El Nino’s help.
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