Scientists issued a stark warning that time is running out to save the Great Barrier Reef as latest surveys showed that two thirds of the ecosystem has been hit by mass coral bleaching within the last two years.
A total of 1,500 km of corals in both the northern and middle sections of the reef have been badly impacted in back-to-back events, said ARC Centre of Excellence for Coral Reef Studies.
Only the southern third of the famed reef has now escaped relatively unscathed.
Professor Terry Hughes, director of the centre, told ITV News that urgent action was needed to stop record-breaking water temperature rises and save the unique ecosystem for future generations.
We have a narrowing window of opportunity to deal with global warming. If we do we will have the Great Barrier Reef - and if don't then we won't.
Reef bleaching is primarily caused by warming waters which leave the living corals several damaged or dead.
Corals take up to ten years to recover after a bleaching, so to see such significant damage inflicted two years in a row is a serious blow.
Dr James Kerry, who also worked on the aerial surveys showing the damage, said: “This is the fourth time the Great Barrier Reef has bleached severely – in 1998, 2002, 2016, and now in 2017.
"Bleached corals are not necessarily dead corals, but in the severe central region we anticipate high levels of coral loss.”
Last year the reef was badly damaged by warm waters in the northern region linked to the El Nino global weather event.
However scientists were concerned to see that this year there was also major bleaching even without such extreme weather.
Prof. Terry Hughes said that it was clear the reef was "struggling with multiple impacts" the most serious of which was global warming.
He said that world leaders must work to limit global warming to two degrees as they agreed at last year's Paris climate summit - or face losing natural treasures forever.
"If we don't adhere to the two degree target and we go along on a business as usual trajectory that would be the end of the Great Barrier Reef and indeed all coral reefs in the world."