scientists trying to send a warning from down under. reporter: it s one of the seven natural wonders of the world. the great barrier rev off the coast of australia, a vibrant underwater ecosystem of coral and sea life that s roughly the size of italy, so huge you can actually see it from space. scientists are sounding the alarm. they say for the second year in a row this sprawling underwater treasure is bleaching on a massive scale. a new study by australia s arc center of excellence for coral rev studies shows approximately two-thirds of the rev is suffering. it s quite terrifying actually. the the magnitude and severity of the event. reporter: sean connolly is one of a team of scientists who have been surveying the damage. a coral is a partnership between an animal which is what builds the skeleton and constructs the reefs that you see and the tiny one-celled algae and hot temperatures cause