Rising ocean temperatures have started a bleaching event that scientists say will affect more coral reefs worldwide than any of the previous three. The National Oceanic and Atmospheric Administration and its international partners made the announcement Monday, the New York Times reports. “The increasing frequency and extremity of marine heat waves driven by climate change is testing the tolerance levels of coral reefs,” said the head of the Australian Institute of Marine Science. “Climate change is the biggest threat to coral reefs worldwide, and this global confirmation illustrates just how e…