A new study finds the world’s great surf breaks are vulnerable to climate change. In Malibu, the problem is more specific: a coast with few defenses, with a record El Niño winter closing in.By Kate WaxmanOn a clean summer swell, the wave at Malibu’s Surfrider Beach arrives from the south, wraps around a cobblestone point and unspools toward the pier in a long, shimmering wave that can carry a surfer for hundreds of feet. It breaks slowly, forgivingly, over rounded stones that were delivered by Malibu Creek across millennia.