Coral reefs have been on this planet for millions of years, but if climate trends continue this century could be their last. In a warming world, reefs and all the marine life they support are on the frontline. A change of just a few degrees can be the difference between life and death. This summer, large parts of the Great Barrier Reef saw the hottest sea temperatures and the most severe coral bleaching ever recorded. Before the next impact hits, scientists are racing against time to understand the demise of reefs and the prospects for their recovery. In this confronting special, Catalyst explores the lethal threat of bleaching to the Great Barrier Reef, and the challenges we all face to protect this global treasure. #ABCcatalyst