Warm water has already begun bleaching coral on the Great Barrier Reef, weeks ahead of the period with the highest forecast risk. Selina Ward, a coral reef biologist from the University of Queensland, said the bleaching appeared to be very localised so far, but was concerning because of how early in the season it was happening. The world’s coral reefs are still reeling from the worst recorded global bleaching event, in which the Great Barrier Reef was hit in both 2016 and 2017. Half the reef’s coral is thought to have been killed. Photos taken by Ward around Heron Island, which escaped significant bleaching during the two previous events, show a large stretch of bleached coral, with some already dead and covered in algae.