A recent report found that all three major regions of the reef experienced bleaching after waters began to warm last December.
A prolonged summer heatwave in Australia has left 91 percent of the Great Barrier Reef's coral damaged by bleaching.
The Great Barrier Reef Marine Park Authority published the Reef Snapshot report late on Tuesday, after it conducted extensive surveys of the World Heritage-listed reef between September 2021 and March 2022.
"Climate change is escalating, and the Reef is already experiencing the consequences of this," the report warned.
The report offered new details of the damage caused by the fourth "mass bleaching" the world's largest coral reef system has experienced since 2016.
It found that after waters began to warm last December, all three major regions of the reef experienced bleaching, a phenomenon that occurs when coral is stressed and expels brightly coloured algae living in it.
'Higher mortality rates'
Although bleached corals are still alive, and moderately affected sections of the reef may recover, "severely bleached corals have higher mortality rates," the report said.
Of the 719 reefs surveyed, the report said 654, or 91 percent, showed some level of coral bleaching.
"Although bleaching is becoming more and more frequent, this is not normal, and we should not accept that this is the way things are," Australian Marine Conservation Society campaigner Lissa Schindler said.
Greenpeace activist Martin Zavan, meanwhile, said fossil fuels were to blame for the coral bleaching.
Next month, the United Nations' World Heritage Committee will decide whether to list the reef as "in danger."
Australia was able to avoid a threatened UN downgrade of the reef's World Heritage status in 2015 by creating a "Reef 2050" plan and pouring billions of dollars into protection.
It was the first time on record the reef had suffered bleaching during a La Nina weather cycle, when cooler temperatures would normally be expected.