"In general, coral reefs have collapsed catastrophically in just the three decades that I have studied them," said Nancy Knowlton, a professor of marine biology at the Scripps Institution of Oceanography in La Jolla , California. Knowlton, who is also a member of the National Geographic Society's Research and Exploration Committee, notes that corals live precariously close to their thermal limits. As a result, even the most isolated coral reefs are vulnerable to the effects of global warming. “The increasingly warm temperatures that we have observed over the last two decades have upended coral reefs in terms of rapid bleaching events,” he said. Graham, the study's author, says that while local and regional resource managers can mitigate some damage to coral reefs, broader action is needed. “Bleaching is a global problem and is caused by global warming,” Graham said. “So the onus is on all of us, really.” "We need to reduce greenhouse gases and address these problems