The latest aerial surveys released by scientists this month show a recent bleaching event almost as severe as the record bleaching of 2016 that left two-thirds of the reef damaged. Bleaching occurs when extreme heat forces algae to abandon coral, turning them pale white.
In 2016, El Niño was responsible for a spike in ocean temperatures, which led to an unprecedented level of bleaching along the northern third of the reef. Scientists found as many as 95 percent of the corals surveyed in 2016 were severely bleached.
Bleaching is not necessarily fatal for coral, but 2016 was also the highest level of coral mortality ever recorded on the Great Barrier Reef. In the worst-affected area, a 435-mile region in the north near Cooktown, Australia, as much as 67 percent of shallow-water corals died.
This year, scientists says climate change and rising ocean temperatures are behind the bleaching of the reef, with bleaching spread further south, hitting the middle third particularly hard. Only the southern third of the reef is unharmed.