Strong El Niño events occurred more frequently over the past century than during the preceding millennium before industrial greenhouse-gas emissions warmed the Earth, according to research reported by Nature. The findings, published in Science by a research team led by Julia Cole, draw on pre-industrial sea surface temperature reconstructions derived from coral skeletons collected in the Galápagos islands.
Cole, a palaeoclimatologist at the University of Michigan in Ann Arbor, examined month-to-month coral growth layers to track historical climate shifts in the eastern Pacific Ocean. Scientists turn to proxy records such as corals, tree rings, and marine fossils because direct temperature measurements across remote tropical Pacific waters are rare prior to the twentieth century. Computer simulations also face ongoing challenges in fully capturing the intricate wind and ocean feedbacks that drive the El Niño–Southern Oscillation.
Earlier proxy records from the central Pacific pointed to an increase in strong events over recent decades. However, those central records failed to capture the eastern Pacific, where El Niño events reach their highest intensity. Julien Emile-Geay, a palaeoclimatologist at the University of Southern California in Los Angeles, compared relying solely on central Pacific data to a doctor attempting to measure a heartbeat by placing a stethoscope on an ankle.
Galápagos corals provide direct measurements from the eastern Pacific, even though extreme local ocean conditions make coral growth rare in the archipelago. The findings coincide with active Pacific conditions that emerged in June, which forecasts indicate could set new intensity records as the third strong El Niño to develop in 11 years.
