More than 90% of the Great Barrier Reef surveyed by researchers was bleached, Australian government scientists say. “Climate change remains the greatest threat to the Reef,” the report said. Rising ocean temperatures cause heat stress for coral, turning them white and increasing their susceptibility to disease. This is the fourth mass bleaching event in seven years, but the first during a La Niña pattern, which coincides with cooler Pacific Ocean temperatures.  (AP, CBS, Weather Channel, HuffPost; Climate Signals background: Coral Bleaching Increase