04/20/2016 02:59 EDT

Coral Bleaching Caused By Climate Change Is Killing The Great Barrier Reef

“That is a mass extinction and there is every reason to believe that we are triggering it.”

Climate change is leaving a very visible mark on the Great Barrier Reef.

More than 90 per cent of its reefs — the world’s largest living ecosystem — are bleaching, The Guardian reported Wednesday.

Bleaching happens when warm water temperatures cause corals to lose the microscopic algae they need for food and colour, turning them white.

Bleached branching coral, photographed in Maldives. (Photo: Reinhard Dirscherl/Getty Images)

Half of the Great Barrier Reef corals are already dead or dying, according to The Independent.

Coral reefs are “unquestionably” the world's most colorful places, National Geographic says, and they're also the ocean’s most diverse marine ecosystems — supporting approximately 4,000 species of fish and 800 kinds of hard coral.

But since 1998, the Great Barrier Reef has been hit by three mass bleachings — the worst of which is happening now.

The biggest cause is global warming, according to the Smithsonian. Bleached corals don’t die right away, but if temperatures don’t cool down, they eventually starve to death or succumb to disease.

A healthy coral reef in Fiji, in all its vibrant glory. (Photo: Reinhard Dirscherl/Getty Images)

This year, a pulse of warm water caused by El Niño, combined with high temperatures from climate change, caused the worst mass bleaching scientists have ever seen, according to The Guardian.

Scientist and coral expert Charlie Veron told The Huffington Post Australia there is no specific temperature change to blame, it was due to cumulation of stress.

The damage could lasts for millions or billions of years, Veron warned.

“Roughly one third of all marine species have got some part of their life cycle in a coral reef. Once you wipe out a coral reef, you are really hitting the oceans — it's beyond imagination,” he said.

“That is a mass extinction and there is every reason to believe that we are triggering it.”

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