Coral reefs pushed to brink as bleaching crisis worsens
Corals turn white under heat stress, which causes them to expel the algae which give them bright colours and nutrients – Copyright POOL/AFP/File Curtis MeansAn unprecedented coral bleaching episode has spread to 84 percent of the world’s reefs in an unfolding human-caused crisis that could kill off swathes of the essential ecosystems, scientists warned Wednesday.…