Climate crisis pushed reefs to ‘tipping point of near-annual bleaching’

Bleached coral on Australia's Great Barrier Reef near Port Douglas on Feb. 20, 2017.

Rising ocean temperatures could have pushed the world’s tropical coral reefs over a tipping point where they are hit by bleaching on a “near-annual” basis, according to the head of a US government agency program that monitors the globe’s coral reefs.

Dr Mark Eakin, coordinator of Coral Reef Watch at the National Oceanic and Atmospheric Administration, told Guardian Australia there was a risk that mass bleaching seen along the length of the Great Barrier Reef in 2020 could mark the start of another global-scale bleaching event.

Tropical coral reefs tend to be at a higher risk of bleaching during times when the Pacific Ocean is in a phase known as El Niño. The latest bleaching on the reef has hit during this cycle’s neutral phase.

“The real concern is with this much bleaching without tropical forcing,” Eakin said. “This may be a sign we’ve now tipped over to near-annual bleaching in many locations.”

“It’s quite concerning that we are getting this much heat stress across the Great Barrier Reef in an Enso [El Niño southern oscillation]-neutral year.

“What we are seeing on the Great Barrier Reef and potentially elsewhere is really being driven just by anthropogenic climate change.

“If we get another El Niño, the odds are almost 100% that we will see another global bleaching event.”

Aerial surveys of 1,020 individual reefs completed across the length of the 2,300km marine park confirmed last week a third mass bleaching event in only five years.

“That’s already pushing awfully close to near-annual bleaching,” added Eakin.

Corals bleach when they sit in abnormally hot water for too long. Reefs and corals can recover from mild bleaching, but severe and prolonged heat stress can kill corals.