SYDNEY, July 5 (Xinhua) -- Australia's iconic Great Barrier Reef could be severely damaged by coral bleaching every two years unless greenhouse gas pollution levels are slashed, a major environmental group warned on Thursday.

The world's largest reef ecosystem could be repeatedly hit with the bleaching unless the emissions are effectively and swiftly cut in the coming decades, according to a Climate Council group report released on Thursday.

One-third of coral across the reef had already died after a mass bleaching event in 2016, with fish populations in some sections also suffering as a result, the group's councillor and ecologist Professor Lesley Hughes said in a statement.

"Severe bleaching, such as the 2016 event that devastated the Great Barrier Reef, have more than quadrupled in over the last thirty to forty years," she said.

"The unprecedented mass coral bleaching of the Great Barrier Reef in 2016 was at least 175 times more likely to occur due to climate change."

Coral bleaching occurs when the reef colonies lose their vivid color in waters that are too warm for the microscopic algae living in them. The bleached corals are physiologically damaged and sustained bleaching will lead to coral death.

The likelihood that the Great Barrier Reef will ever fully recover or return to its pre-bleaching state is low and there is little evidence that improving water quality can sufficiently reduce susceptibility of corals to bleaching from marine heatwaves, according to the council.

Global sea surface temperatures have risen by more than 0.2 degrees Celsius from 1992 to 2010, increasing the odds of more frequent and prolonged marine heatwaves, it said.

"Doing anything other than urgently and dramatically slashing our nation's rising greenhouse gas pollution levels will essentially sign the death certificate for the Reef as we know it today," said the council's Acting CEO Martin Rice.