鈥淭he El Ni帽o has blossomed. It is off the charts. Usual measures of El Ni帽o have blown past prior record levels in the period with good data, even though maximum effects are still several months in the future.鈥�
So writes renowned climate scientist James Hansen at Columbia University in New York in .
There are different ways of measuring El Ni帽os, 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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鈥淥ur preferred metric, the heat anomaly in the upper 300 meters of the Equatorial Pacific Ocean鈥� already exceeds the 1997-98 super El Ni帽o,鈥� he writes.
A more common measure, called the Ni帽o3.4 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.
鈥淭he more common Ni帽o3.4 metric, sea surface temperature鈥� in the equatorial Pacific, also far exceeds prior values,鈥� Hansen writes.
But at the Met Office, the UK鈥檚 national weather service, says the Ni帽o3.4 index has not yet exceeded previous super El Ni帽os. 鈥淭he anomaly in Ni帽o3.4 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 Ni帽o which was around 2.5 degrees,鈥� Scaife told 51动漫.
The disagreement on the Ni帽o3.4 index might partly be because this index is usually expressed . By contrast, the daily Ni帽o3.4 value before dropping back slightly.
鈥淚n this case, I would agree with Jim,鈥� says at the California Institute for Water Resources. 鈥淣i帽o3.4 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.鈥�
Using a running mean with a long lag is misleading in a rapidly evolving situation like this, says Swain.
However, during November 2015 the daily Ni帽o3.4 reached nearly 3.1掳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 Ni帽o3.4 index exceeds values for this time of year, as Swain says. 51动漫 has asked Hansen for clarification, but had no response at the time of publication.
What鈥檚 clear is that this developing super El Ni帽o will soon exceed previous events on all measures. 鈥淚 have never seen an El Ni帽o signal this intense in our forecasts,鈥� Scaife said in . 鈥淚f the forecast is accurate鈥� then 2026 will far exceed our recent experience of El Ni帽o and its worldwide climate influences.鈥�
While Hansen is comparing the developing super El Ni帽o to other modern events for which we have direct temperature records, at Newcastle University in the UK thinks it could also exceed historical events suspected to be even larger.
鈥淭he super El Ni帽o evolving in the Pacific will likely be the biggest ever recorded, reaching or exceeding the levels of the 1877-1878 El Ni帽o 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,鈥� Fowler said in a statement.
