The new findings don't rule out the possibility that global warming could be behind recent El Niño and La Niña trends. But the historical perspective makes it impossible to conclude that human-caused climate change is to blame for the recent shifts. It may be that ENSO is just naturally variable, regardless of external conditions.
"Relatively robust 20th-century ENSO variability may reflect a sensitivity to anthropogenic greenhouse forcing," the researchers wrote. "But definitive proof of such an effect requires much longer data sets than are currently available, given the large range of natural ENSO variability implied by the available fossil coral data."
Photo: Fossil coral "rocks" located on beaches in the Line Islands provide detailed records of temperature and precipitation useful for understanding ENSO events. Credit: Jordan Watson