The Marshall Islands is experiencing its worst-ever coral bleaching as global warming threatens reefs across the entire northern Pacific, scientists said on Monday. Marine researchers said an El Nino weather pattern had been developing in recent months, raising ocean temperatures and stressing delicate coral reefs. "The worst coral bleaching event ever recorded for the Marshall Islands has been occurring since mid-September," Karl Fellenius, a Majuro-based marine scientist with the University of Hawaii told AFP. C. Mark Eakin, manager of the US National Oceanic and Atmospheric Administration's Coral Reef Watch programme, said recent observations showed the problem was widespread across the vast waters of the northern Pacific. "Major bleaching was seen in Guam and the Commonwealth of the Northern Marianas Islands, the northwestern Hawaiian Islands (NWHI), the Marshall Islands, and Kiribati," he said.