This year’s El Niño just broke a record months before it’s expected to peak

Warnings of an El Niño unlike any other are starting to become reality. For months, scientists have cautioned that the natural climate pattern could grow into a record-breaking beast, releasing extraordinary amounts of heat from the ocean and fueling droughts, floods, heat waves and severe storms. Now, a traditional strength measurement of El Niño, called the Oceanic Niño Index, indicates that the pattern has reached an intensity unseen in recorded history.

On September 21, the daily sea surface temperature in the region where El Niño develops — the central and eastern equatorial Pacific Ocean — reached 3.08 degrees Celsius warmer than the 1991 to 2020 average. That’s more extreme than any other El Niño ever recorded. Since El Niño emerged in June, the daily average sea surface temperature has climbed extraordinarily high in the heart of the Pacific Ocean region where El Niño develops.

On September 21, it reached 3.08 degrees Celsius above both the 1991 to 2020 average (coarse dashed line) and the 1982 to 2010 average (fine dashed line). Prior to this month, the most extreme anomaly on record was 3.02 degrees Celsius, set by an El Niño in November 2015. What’s more, the El Niño will probably grow even stronger, Johnson says.

NOAA has yet to declare this event the strongest on record. It uses a rolling three-month-average anomaly, rather than the daily anomaly, in calculations of an El Niño’s strength. And it’s shifted to a new method for measuring El Niño strength, called the Relative Oceanic Niño index, which better represents the phenomenon’s ability to sway weather globally.

By that measurement, the current El Niño has yet to surpass the strength of the one in 1997 and 1998. But that record is on track to be broken soon, the latest seasonal forecast from NOAA’s Climate Prediction Center suggests. To understand what’s driving this historic El Niño and its potential impact, Science News spoke with Johnson, who is part of the team that produces the forecasts, and Nathan Lenssen, a climate scientist at the National Center of Atmospheric Research in Boulder, Colo.

The conversation has been edited for length and clarity. SN: How much of this El Niño’s strength has been fueled by human-caused climate change? Johnson: It’s really an unanswered question.