El Niño has continued to strengthen to what some scientists are calling "unprecedented levels", weeks before its expected peak in December. Several key measures are now in record territory. In its latest update, Australia's Bureau of Meteorology (BOM) said average weekly sea-surface temperatures in the central Pacific have reached their highest level on record, external.
It comes after scientists declared a new record for daily sea surface temperatures in the central-eastern Pacific in September, exceeding the previous record set during the very strong El Niño of 2015. Temperatures above 30C have also been recorded for the first time in parts of the tropical Pacific, while record sea-surface temperature anomalies and exceptional subsurface warmth have been observed. These measurements come from the region of the equatorial Pacific used to monitor El Niño.
El Niño is a naturally-occurring pattern, which happens about every two to seven years and tends to last for around a year. However, the Pacific is also warming due to human-induced climate change and this is starting to mask the strength of the natural warming during El Niño. To remove this additional warming signal, Australian and US official forecasters are now using a Relative Ocean El Niño Index (RONI), to enable better comparison to historical events.
Using that measure, the BOM's average weekly data - while only going back to 2008 - is significant as it now exceeds levels during the record-breaking December of 2015. "We are currently witnessing an El Niño event that is unprecedented in the historical record," Dr Zeke Hausfather, a climate scientist at Berkeley Earth, told the BBC. The warmth across the Pacific now extends well beyond the tropical region normally used to monitor El Niño.
Comparisons with previous major events in 1972-73, 1982-83, 1997-98 and 2015-16 show much more widespread ocean warmth across the Pacific and into the Gulf of Mexico. Part of this reflects the long-term warming of the oceans but scientists say it is not the whole story. "The strength of El Niño this year is spilling out of the traditional El Niño region," Dr Hausfather said.
Developing El Niño becomes strongest on record weeks before expected peak What is El Niño and why could it mean record temperatures? The World Meteorological Organization (WMO) says there is currently no evidence that climate change is making El Niño events stronger or more frequent, external. However, it remains an active area of scientific research.
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