Flooded streets followed the arrival of Hurricane Polo in Puerto San Carlos, Baja California Sur, Mexico, on 29 September. The Category 3 storm added to an already busy hurricane season turbocharged by El Niño. This year, El Niño has continued to strengthen to what some scientists are calling "unprecedented levels," weeks before its expected peak in December.
Record Sea Temperatures
Several key measures are now in record territory. In its latest update, Australia's Bureau of Meteorology (BOM) reported that average weekly sea-surface temperatures in the central Pacific have reached their highest level on record. This follows a declaration of 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.
El Niño this year is creating new ocean temperature records against a backdrop of overall ocean warming due to human-induced climate change. Notably, temperatures above 30°C have been recorded for the first time in parts of the tropical Pacific, alongside record sea-surface temperature anomalies and exceptional subsurface warmth.
Understanding El Niño
El Niño is a naturally occurring pattern that happens approximately 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, which is starting to mask the strength of the natural warming during El Niño. To account for this additional warming signal, Australian and US official forecasters are now using a Relative Ocean El Niño Index (RONI) for better comparison to historical events.
Using this measure, BOM's average weekly data—though only dating back to 2008—is significant as it now exceeds levels recorded during the record-breaking December of 2015.
“"We are currently witnessing an El Niño event that is unprecedented in the historical record," said Dr. Zeke Hausfather, a climate scientist at Berkeley Earth.
