Two-thirds of the Great Barrier Reef is bleached from climate change

Two-thirds of the Australia’s Great Barrier Reef – an estimated 900 mile (1,500 km) stretch of the UNESCO World Heritage Site – have been damaged by “unprecedented” bleaching over the past two years, researchers from James Cook University in Queensland have revealed.

Aerial surveys conducted by Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at the university and his colleagues discovered bleaching in back-to-back years for the first time ever, according to BBC News and the Washington Post.

While last year, the northern part of the reef was hit hard by bleaching, this year the majority of the damage was suffered in the middle section, the climate scientists discovered. In light of their discovery, experts are concerned that there is little hope of recovery for the damaged coral.

“Last year we lost 67 percent… of the corals in the northern 700 kilometers (430 miles) of the barrier reef, between March and October. We’re likely to see something similar happen now in the middle third this year,” Hughes told the Post. “That’s obviously an enormous loss over two-thirds of the Great Barrier Reef.”

“I wouldn’t say the barrier reef is dying. But clearly, we’re measuring serious losses here,” he added. “And the reason it’s happening is global warming.”

‘Window’ to deal with climate change ‘is rapidly closing’

That’s obviously bad news for a place that, according to BBC News, has been called the “most biodiverse” of the planet’s World Heritage sites and an area of “enormous scientific and intrinsic importance.” The 1,400 mile (2,250 km) reef is the largest structure of its kind on Earth.

Coral bleaching occurs as a result of unusual increases in water temperature – a naturally-occurring phenomenon that is believed to be made worse by human-caused climate change. An estimated 93 percent of all increases in the Earth’s heat are absorbed by oceans, and when that happens, it causes corals to become stressed, resulting in the loss of photosynthetic algae.

The loss of that algae, better known as zooxanthellae, causes the coral to lose their color and turn while, indicating that their metabolism has been disturbed. If conditions are returned to normal, then the corals can recover in a few decades but is the stress is not alleviated, the corals can die. With bleaching events recorded in consecutive years, scientists are concerned that the reef might not be able to recover.

“Bleached corals are not necessarily dead corals, but in the severe central region we anticipate high levels of coral loss,” Dr. James Kerry, who led the aerial surveys, told Sky News. “It takes at least a decade for a full recovery of even the fastest growing corals, so mass bleaching events 12 months apart offers zero prospect of recovery for reefs that were damaged in 2016.”

“Clearly the reef is struggling with multiple impacts. Without a doubt the most pressing of these is global warming. As temperatures continue to rise the corals will experience more and more of these events. Ultimately, we need to cut carbon emissions, and the window to do so is rapidly closing,” added Hughes, who went on to tell BBC News, “The sooner we take action on global greenhouse gas emissions and transition away from fossil fuels to renewables, the better.”

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Image credit: Ed Roberts/ARC

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