Coral reef samples dating back to 130,000 years ago reveal that the weather phenomenon known as the El Nio Southern Oscillation (ENSO) has experienced an unparalleled intensification over the past century. The new findings, published today in Sciencexpress, could figure importantly in determining the influence of global warming on this event.
In order to peer into El Nio's past, David W. Lea of the University of California at Santa Barbara and his colleagues turned their attention to corals in Papua New Guinea. Samples of the fossil corals there, they reasoned, would provide "climatic windows" on the past 130,000 years, while cores from living corals would enable the team to calibrate the coral record and the instrumental record of El Nio over the past 100 years.
Subsequent chemical and isotopic analyses of the ancient cores revealed the temperature and salinity of the water in which the corals had once lived, which in turn provided the basis for reconstructing climate. The results indicate that whereas during the Ice Age, El Nio was at its weakest (its strength diminished by about 50 percent), warm periods brought the strongest El Nio events. Most striking of all, it appears that over the past 130,000 years, El Nio intensity has reached an all-time high in the past century alone.
Although the jury is still out on what accounts for El Nio's recent surge in strength, the team's coral record data offer tantalizing clues. Indeed, University of Arizona researcher Julia Cole writes in a commentary accompanying the report that "their results provide strong support for the idea that ENSO may be more responsive to global change than previously thought."