Australia’s spectacular Great Barrier Reef is suffering “mass bleaching” as corals lose their colour under the stress of warmer seas, authorities said Friday, in a blow widely blamed on climate change. The world’s largest coral reef system, stretching for more than 2,300 kilometres (1,400 miles) along the northeast coast of Australia, is showing the harmful effects of the heat, said the Reef Authority. Aerial surveys detected coral bleaching at multiple reefs across a large area of the system, “confirming a mass bleaching event, the fourth since 2016,” it said in a report. The Great Barrier Re…