Matt Golding Credit: "It is important not to lose optimism by thinking the job is too big, or to think that a changed reef is far in the future - actions taken now will matter," the report said. Back-to-back mass bleaching in the summers of 2016 and 2017 resulted in the deaths of about half the corals amid marine heatwaves. At certain temperatures, stressed corals expel the algae that give them most of their energy and colour, turning them pale and often killing them. "Gradual sea temperature increase and extremes, such as marine heat waves, are the most immediate threats to the reef as a whole and pose the highest risk," the authority's chief scientist David Wachenfeld said in a statement. "Global action on climate change is critical." In an opinion piece for the Herald and The Age, Environment Minister Sussan Ley said the reef wasn't "dead" and still had "vast areas of vibrant coral and teeming sea life, just as it has areas that have been damaged by coral bleaching, illegal fishing and crown of thorns outbreaks".

"There are those who will not be happy unless we declare the reef dead in the name of climate change, just as there are those who want to claim that nothing out of the ordinary is taking place," she wrote. The report came hours after the Morrison government released the latest national greenhouse gas emissions data that show emissions for the 12 months to March had exceeded those of any year since the 2012-13 financial year. Loading Separately, the inshore reef scored a "D" for overall condition, according to the annual Reef Report Card – released on Friday by the federal and Queensland governments. The score is based on the state of coral, seagrass and water quality, and matches the rating for seven of the past eight reports. "We know the reef is resilient," said Richard Leck, head of oceans at the World Wide Fund for Nature. "Action on climate change and water quality will give [it] the best opportunity to survive global warming.

"The Reef 2050 Plan is required to be revamped next year and must take climate change seriously and regulations to reduce farm runoff currently before the Queensland Parliament must be passed," he said. "The science is irrefutable - the time for delay is over." The reef covers 346,000 square kilometres and while it faced "enormous challenges", tourists would find it "awe inspiring", Ms Ley wrote, adding 64,000 jobs continue to rely on it. Loading The Wilderness Society's Jess Panegyres said it was notable the outlook report emphasised the impacts of land clearing in adjacent catchment areas. “This report makes clear that ongoing deforestation is a direct threat to the health of the Great Barrier Reef," Ms Panegyres said. "It explicitly links high levels of clearing in recent years to the wind-back of native vegetation laws by the former Queensland coalition government."