From Science Magazine:
“Kim Cobb and two team members, clad in black scuba gear, have been scouring the coral-studded seabed near the equatorial Pacific’s Christmas Island here for nearly an hour. Then Cobb emerges with a victorious “Yes!”
A few minutes later, Cobb, a paleoclimatologist at the Georgia Institute of Technology in Atlanta, dives back to the bottom and, from under a coral head, extracts the prize: two small containers encrusted with coralline algae. Inside are recorders of salinity and temperature that captured in excruciating detail the 2015–16 El Niño event, which brought a pulse of abnormally warm water to the tropical Pacific. The recorders showed that during the disturbance, which wreaked climatic havoc around the globe, the warming here set a record: 3°C above normal. The extreme warmth, Cobb says, reflected not just the natural El Niño cycle, but a new factor: global warming caused by human activity.
As she will report next week at the American Geophysical Union meeting in San Francisco, California, a detailed, long-term temperature record derived from corals on Christmas and other Pacific islands shows that over the last 7000 years, El Niños waxed and waned. Then, during the 20th century, with global warming taking hold, their intensity began to climb. The trend is likely to continue, boding ever more destructive El Niños, she says. “It’s yet another impact of global warming that we’d like to avoid.”