A bleak new study describes the profound damage that climate change has wreaked on Australias Great Barrier Reef. Rising temperatures in 2016 cooked swathes of corals, the scientists found, causing the catastrophic die-off of almost 30 percent of the worlds largest coral reef system.

Global warming has already radically and possibly permanently transformed the reefs ecology, according to the study, published Wednesday in the journal Nature. If action is not taken promptly and comprehensively to curb warming, it could be game over for the reef, scientists warned.

Its catastrophic, Sarah Perkins-Kirkpatrick, a New South Wales-based climate researcher who was not involved in the new study, told Australias ABC News after reviewing the research. There might have been a glimmer of hope that it wasnt as bad or might recover faster than we thought. But this paper made the reality very present. The bleaching will forever change the Barrier Reef.

The extent of the coral die-offs in 2016 and another severe bleaching event in 2017 had already been known to scientists, but the new research chronicled specifically how rising temperatures had affected different reef species and the reefs ecological health at large.

The studys authors said they were alarmed by their findings.

Though some coral species proved more resilient to rising temperatures, some died much more rapidly than expected.

The conventional thinking is that after bleaching, corals died slowly of ... starvation. Thats not what we found. We were surprised that about half of the mortality we measured occurred very quickly, Terry Hughes, the authors lead author, told The Guardian .