It’s the first time that a mass bleaching has happened during a La Niña year, when the ocean is supposed to be cooler than usual.
Reef scientists have called for urgent action on climate change or humanity could have a very different underwater world by midcentury.
If global warming trends continue, the Great Barrier Reef will be destroyed.
“I’m not sure I have the fortitude to do this again,” one of Australia's top scientists wrote.
The iconic structure was hit with devastating, back-to-back bleaching in 2016 and 2017.
The catastrophic die-off from recent ocean heat waves severely affected the reef's ability to produce new corals and bounce back.
Hawaii also banned the sale and distribution of similar sunscreens, which contain chemicals that lead to coral bleaching.
Last year's oceanic heat wave wasn't as destructive as one the year before, scientists said.
New report examines experimental intervention techniques in hopes of sustaining reefs in a warming world.
Rising temperatures in 2016 caused a catastrophic die-off of almost 30 percent of the iconic reef.