‘Off the charts’ El Niño is already the strongest since records began
Renowned climate scientist James Hansen says the developing super El Niño has already "blown past" previous events with months to go before it peaks
“The El Niño has blossomed. It is off the charts. 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.
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“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.
“The more common Niño3.4 metric, sea surface temperature in the equatorial Pacific, also far exceeds prior values,” Hansen writes.
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 anomaly in Niño3.4 is currently about 2 degrees above the norm which is very high for this time of year but not quite as high as the anomaly at the peak of the 1997/1998 El Niño which was around 2.5 degrees,” Scaife told New Scientist.
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.
“In this case, I would agree with Jim,” says Daniel Swain at the California Institute for Water Resources. “Niño3.4 values are clearly now the highest on record for the time of year, and are expected to remain so for the rest of the calendar year.”
Using a running mean with a long lag is misleading in a rapidly-evolving situation like this, Swain says.
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. “I have never seen an El Niño signal this intense in our forecasts,” Scaife said in a statement released today. “If the forecast is accurate, then 2026 will far exceed our recent experience of El Niño and its worldwide climate influences.”
While Hansen is comparing the developing super El Niño to other modern events for which we have direct temperature records, Hayley Fowler at Newcastle University in the UK thinks it could also exceed historical events suspected to be even larger.
“The super El Niño evolving in the Pacific will likely be the biggest ever recorded, reaching or exceeding the levels of the 1877-1878 El Niño which caused widespread impacts, including famines and around 50 million deaths (3-4 percent of the global population at the time), mostly across Asia and South America,” Fowler said in a statement.
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