This has been the saddest research trip of my life, almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef. We flew for 4000 kilometers (2,485 miles) in the most pristine parts of the Great Barrier Reef and saw only four reefs that had no bleaching. The severity is much greater than in earlier bleaching events in 2002 or 1998.