36 per cent in 29 corals
A team led by Julia Cole at the University of Michigan read strontium-calcium ratios and oxygen isotopes in 29 fossil corals from the Galápagos Islands and reconstructed about 900 years of sea temperature. The study, published in Science, puts El Niño events roughly 36 per cent stronger than before the industrial era, and 16 per cent of that rise sits in the past 40 years. The event now under way is running 2.7 degrees Celsius above normal.[1]
The series that can test it runs about 75 years
The measurement does not come from thermometers directly. The corals stand in for sea surface temperature, and the instrumental series that can test them reaches back only about 75 years. The about 900-year reconstruction has to rest on that short overlap.[1]
Two researchers outside the work, Michael Mann and John Bruno, said recent Galápagos measurements point the other way, showing a substantial decline in peak water temperatures over recent decades. Cole answered that El Niño's own swings can hide a trend across a short window.[1]
Where 900 years and 75 years overlap
The binding test of the reconstruction sits in the about 75 years of the instrumental series; the coral's about 900 years are tested in that overlap. Cole's answer supplies a mechanism: El Niño's own swings can hide a trend across a short window. The other reading remains in place: the decline in peak water temperatures in recent Galápagos measurements may be the local signal, and the coral reconstruction may overstate the change over recent decades. The place to watch is whether coral and instrumental series agree over that 75-year overlap. The event now under way, at 2.7 degrees Celsius above normal, is one season inside that short window.[1]