A coral bleaching event is hitting the globe for just the third time on record, scientists say, and could lead to the biggest coral die-off in history, reports the Guardian. We could lose about 5% of the planet's corals (or 4,500 square miles) this year, while 38% may be affected. Similar events in 1998 and 2010 each lasted a year, but this event—caused by warming oceans as a result of global warming, El Nino, and a warm "blob" in the Pacific Ocean—started last year and is likely to last into 2016, putting corals "under really prolonged stress," says NOAA researcher Mark Eakin, per the Washington Post and Discovery News. When stressed, corals lose the symbiotic algae that provide color and thus turn white. They can recover, but death often follows long-term events.
About 95% of US coral reefs will encounter temperatures that can cause bleaching this year, while 60% are likely to be "hit with severe thermal stress," says Eakin. "We've been hearing worrying reports of bleaching from various places … with worse news likely yet to come with the strengthening El Nino," a coral expert from the Smithsonian Institution tells the Post. A University of Queensland scientist expects a bleaching event to occur every year by 2030. "Coral reefs are the underwater equivalent of rainforests, and by removing the corals, you remove the trees of that underwater world," adds another expert. About 500 million people rely on reefs for food or their livelihood. (In better news, researchers found a massive new reef in Australia.)