Study Links Stronger El Ninos to Human-Caused Climate Change

A new study published in the journal Science suggests El Ninos — the periodic climate pattern that temporarily warms parts of the equatorial Pacific and spikes global temperatures — have grown more than 36% stronger since before the industrial age began in the mid-1800s, with a 16% jump in just the last 40 years alone. Study lead author Julia Cole, a paleoclimate scientist at the University of Michigan, said the increase in El Nino's strength closely tracks the rise in global temperature caused by human activities such as the burning of fossil fuels.

Cole's team studied 29 fossil corals from the Galapagos Islands, the oldest dating back to around the year 1100, to reconstruct El Nino strength over roughly 900 years. Measuring the ratio of calcium to strontium and different oxygen isotopes in the coral skeletons reveals the seawater temperature in which they formed, while measuring uranium and thorium tells researchers when each skeleton formed.

El Nino is measured by comparing a three-month average water temperature in the central Pacific to normal; 0.5 degrees Celsius warmer counts as an El Nino, and 2 degrees Celsius or more is rated "very strong." The El Nino currently under way was at 2.7 degrees Celsius by the latest weekly reading and is forecast to keep strengthening for another two to four months, according to Columbia University's El Nino tracker, potentially making it the biggest on record.

Dalhousie University marine scientist Boris Worm, who was not part of the study, said El Nino is "the most violent aspect of climate variability worldwide," with effects ranging from fisheries collapse to coral die-offs, droughts and food shortages. Brown University coral and climate scientist Kim Cobb, also not involved in the study, called coral records "the gold standard for El Nino reconstruction" and said the new data adds to evidence of intensifying El Ninos. The study's reception among outside scientists was mixed, though, with some questioning how it fits with recent observations.