El Nino has continued to strengthen to what some scientists are calling "unprecedented levels", weeks before its expected peak in December, with several key measures now in record territory, BBC Weather reports.
In its latest update, Australia's Bureau of Meteorology said average weekly sea-surface temperatures in the central Pacific have reached their highest level on record. That follows the declaration in September of a new record for daily sea-surface temperatures in the central-eastern Pacific, exceeding the previous mark set during the very strong El Nino of 2015.
Temperatures above 30C have also been recorded for the first time in parts of the tropical Pacific, alongside record sea-surface temperature anomalies and exceptional subsurface warmth. The measurements come from the stretch of the equatorial Pacific used to monitor El Nino.
El Nino is a naturally occurring pattern that arrives every two to seven years and tends to last about a year. The Pacific is also warming because of human-induced climate change, and that background warming is starting to mask the strength of the natural warming during an El Nino event.
To remove the extra signal, Australian and US official forecasters are now using a Relative Ocean El Nino Index, or RONI, which is intended to allow better comparison with historical events. The Bureau's average weekly data on that measure goes back only to 2008, and now exceeds the levels seen in the record-breaking December of 2015.
"We are currently witnessing an El Nino event that is unprecedented in the historical record," Dr Zeke Hausfather, a climate scientist at Berkeley Earth, told the BBC.
The warmth now extends well beyond the tropical region normally used to monitor the pattern. Comparisons with the major events of 1972-73, 1982-83, 1997-98 and 2015-16 show much more widespread ocean warmth across the Pacific and into the Gulf of Mexico. "The strength of El Nino this year is spilling out of the traditional El Nino region," Hausfather said.
The World Meteorological Organization says there is currently no evidence that climate change is making El Nino events stronger or more frequent, though it remains an active area of research. What is clearer is that El Nino releases additional heat from the oceans into the atmosphere, and that is expected to help make 2026 one of the warmest years on record, with unusually high global temperatures likely to continue into 2027.
The instrument at the centre of this deserves a paragraph of its own. Because the ocean is warming for reasons that are not El Nino, forecasters have adopted an index that subtracts the warming that is not El Nino, so that El Nino can be compared with earlier El Ninos.
This newspaper regards the solution as elegant. The Pacific is now setting records on a measure specifically designed not to notice the thing making it warmer, and the records are being set weeks early.
The yardstick's own biography should also be entered into the record. The Bureau's weekly figures on this index begin in 2008, which makes the historical record in which the event is unprecedented eighteen years long.
The Department of Unnecessary Research notes the remaining difficulty, which is geographical. The warmth has spread outside the box used to define El Nino, so a share of the present event is now, strictly speaking, not El Nino at all.
The water on either side of that boundary is the same temperature. Only the index can tell them apart.