Australia’s Great Barrier Reef has been hit with a sixth mass coral bleaching event, the marine park’s authority has confirmed, with aerial surveys showing almost no reefs across a 1,200km stretch escaping the heat, as reported by the Guardian.

The confirmation from the Great Barrier Reef Marine Park Authority (GBRMPA) marks an alarming milestone for the ocean icon, with 2022 going down as the first time mass bleaching has happened in a cooler La Niña year which scientists had hoped would be a period of recovery for corals.

Dr David Wachenfeld, GBRMPA chief scientist, told the Guardian bleaching wasn’t expected in a La Niña.

“But having said that, the climate is changing and the planet and the reef is about 1.5 degrees centigrade warmer than it was 150 years ago. Because of that, the weather is changing. Unexpected events are now to be expected. Nothing surprises me anymore.

Coral bleaching happens when the animal becomes stressed from above-average water temperatures. The coral animal expels the algae that live inside them and provides the coral with food and color.

Widespread mass bleaching of corals on the reef was first seen in 1998, and happened again in 2002, 2016, 2017, 2020 and now 2022.