More than one-third of corals on the northern and central Great Barrier Reef have suffered bleaching due to global warming and acidification of the ocean, scientists said Monday.The impact is still unfolding, researchers from the ARC Centre of Excellence for Coral Reef Studies said following months of aerial and underwater surveys.At least 35 per cent of corals on that part of the reef are affected, the scientists said."The recovery of coral cover is expected to take a decade or longer, but it will take much longer to regain the largest and oldest corals that have died," the group said."This year is the third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we've measured before," said Terry Hughes, director of the research centre."We're rapidly running out of time to reduce greenhouse gas emissions," he said.Last month, the same team of scientists said an aerial survey showed that coral bleaching had affected 93 per cent of the Great Barrier Reef.Bleaching is caused by a die-off of the living organisms, or algae, inside the coral. It can be triggered by small changes in environmental conditions, like a rise in sea temperature.It is the loss of these colourful algae that causes the corals to turn white and "bleach."Scientists say mildly bleached corals can recover from a warming if the temperature drops again soon, and the algae is able to recolonize them. Otherwise, the coral may die permanently.On Friday, it was reported that Australia pushed to have a whole chapter on the Great Barrier Reef removed from a UN report on climate change, fearing it would impact tourism.The Great Barrier Reef is one of Australia's main tourist attractions, generating five billion Australian dollars (3.9 billion US dollars) per year and providing some 70,000 jobs.Mia Hoogenboom, a researcher with the centre and a professor at James Cook University, said more than 95 per cent of corals in the south section of the reef have survived."We expect these more mildly bleached corals to regain their normal colour over the next few months," she said.The stress from coral bleaching is likely to temporarily slow their reproduction and growth rates, the centre said, adding that the southern reefs escaped damage because water temperatures were closer to the normal summer conditions.