Usual measures of El Niño have blown past prior record levels in the period with good data, even though maximum effects are still several months in the future.” So writes renowned climate scientist James Hansen at Columbia University in New York in a newsletter sent today. There are different ways of measuring El Niños, which occur when warm surface waters spread eastwards along the equator across the surface of the tropical Pacific Ocean. Hansen thinks the best measure is how much warmer than usual the upper 300 metres of the eastern tropical Pacific becomes.
This El Niño will be the hottest by a huge margin “Our preferred metric, the heat anomaly in the upper 300 meters of the equatorial Pacific Ocean, already exceeds the 1997-98 super El Niño,” he writes. A more common measure, called the Niño3.4 index, is based on how much warmer than usual the sea surface temperature is in the Pacific in the long rectangle between 5 degrees north and south of the equator, and between 120 and 170 degrees west. But Adam Scaife at the UK’s Met Office Hadley Centre, says the Niño3.4 index has not yet exceeded previous super El Niños.
The disagreement on the Niño3.4 index might partly be because this index is usually expressed as a 3 or 5-month running mean. By contrast, the daily Niño3.4 value hit 2.75°C on 8 August before dropping back slightly. The looming El Niño could be bad – but much worse is to come However, during November 2015 the daily Niño3.4 reached nearly 3.1°C, so the current event is not yet as strong as the 2015 one on this measure, either.
It appears Hansen meant to say the Niño3.4 index exceeds values for this time of year, as Swain says. New Scientist has asked Hansen for clarification, but had no response at the time of publication. What’s clear is that this developing super El Niño will soon exceed previous events on all measures.
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