Climate Council professor Lesley Hughes said there were reports of bleaching that had already occurred at three sites off Cape York, in Far North Queensland.

“If those temperatures are maintained there is definitely a heightened risk of bleaching over the next few weeks with a potential peak in the second week of March,” she said.

“It’s very, very concerning.”

Reef on high alert

The National Oceanic and Atmospheric Administration has placed the Great Barrier Reef on Alert Level 1 for the next seven days, meaning significant bleaching is likely.

Professor Hughes said bleaching could have devastating consequences for the World Heritage-listed marine park.

The summers of 2016 and 2017 saw back-to-back mass bleaching, which wiped out half of all shallow-water coral on the Great Barrier Reef.

“If we get bleaching in the northern parts again this year certainly there won’t have been enough time for those reefs that were previously bleached a couple of years ago won’t have had time to recover,” Ms Hughes said.

“It’s sort of insult, upon insult, upon insult to this ecosystem.”

The Australian Marine Conservation Society said another bleaching event was “the last thing” the reef and its coastal communities needed.

“Unfortunately we are a whisker away from bleaching disaster yet again because of global warming driven marine heatwaves,” campaigner Shani Tager said.

“As underwater heatwaves threaten once again to cook our corals, our politicians must move beyond half-baked plans to tackle global warming.”

The Great Barrier Reef Marine Park Authority has been contacted for comment.