How much of the Great Barrier Reef is bleached?
Coral bleaching
{'answer_start': array([330]), 'answer_text': array(['between 29 and 50'], dtype=object)}
Above-average sea water temperatures caused by global warming is the leading cause of coral bleaching.[2] According to the United Nations Environment Programme, between 2014 and 2016 the longest recorded global bleaching events  killed coral on an unprecedented scale. In 2016, bleaching of coral on the Great Barrier Reef killed between 29 and 50 percent of the reef's coral.[3][4][5] In 2017, the bleaching extended into the central region of the reef.[6][7] The average interval between bleaching events has halved between 1980 and 2016.[8]