Fish swim over a patch of bleached coral in Hawaii's Kaneohe Bay off the island of Oahu in 2015. Warmer water is repeatedly causing mass global bleaching events to Earth's fragile coral reefs. Before 1998 there had been no global mass bleaching events — which turn the living coral white and often lead to death. But there have been three from 1998 on.  (Caleb Jones/AP)
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