The Strongest El Niño Ever - by Zeke Hausfather

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The Strongest El Niño Ever<br>With all the July runs in, dynamical models give a ~90% chance of a record-setting event

Zeke Hausfather<br>Jul 13, 2026

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I’m generally pretty measured in how I discuss climate data. There has been only one time in recent years when I was truly shocked: when global temperatures came in for September 2023 at a full 0.5C warmer than any prior September on record.1 Once until today, that is. With the July runs now in from 667 ensemble members across 14 different seasonal forecast models, it looks like this year’s El Niño is not only very likely to be the strongest event since reliable records began – it may end up the strongest by a truly mind-blowing margin.

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The multi-model median for the event’s peak (measured as detrended sea surface temperature anomalies in the Niño 3.4 region of the tropical Pacific) currently stands at 3.6C, roughly 0.8C hotter than the prior record of 2.75C set in 2015-16. For context, the gap between the strongest and the fifth strongest El Niño of the past 150 years is only about 0.5C. The models are forecasting something outside the envelope of anything we have ever observed.

Peak monthly Niño 3.4 anomaly for every El Niño event since 1877, with each event measured against its own era’s centered 30-year climatology (the ONI convention, applied at monthly resolution to match the forecasts’ monthly values). Events after 1950 (blue) use ERSSTv5; earlier events (open gold) use the HadISST reconstruction. The 2026-27 forecast shows the weighted median of 667 ensemble member peaks from 14 models (July 2026 initializations, members weighted so each model counts equally), with the bar spanning the middle 80% of members.<br>A few things stand out in this figure. First, no event in a century and a half of observations has ever pushed meaningfully past 2.75C. The legendary 1877-78 event comes closest, in a statistical dead heat with 2015-16 (2.73C vs 2.75C, well within the uncertainty of 19th-century ship data). Second, the middle 80% of this year’s forecast ensemble sits entirely at or above that all-time record: even the low end of the plume (2.8C) grazes it. Around 91% of ensemble members exceed the 2015-16 record at their peak.<br>To see what this would look like as the event unfolds, we can compare the forecast trajectory against the five strongest events ever observed, month by month through the development year and into the following spring.

Monthly Niño 3.4 anomaly trajectories for the five strongest observed El Niño events across their development year and decay, against the 2026-27 multi-model forecast. Note that the expected peak (3.6C) sits slightly above the top of the dashed median trajectory (3.5C): individual models peak in different months (e.g. CFSv2 in November, ECMWF in December) so the median of the individual model peaks runs a bit higher than the peak of the median line.<br>What is remarkable here is not just the level but the trajectory. The 2026 event is developing faster than 1997-98, the previous gold standard for explosive El Niño onsets. And unlike 2015 which started its year already warm from a precursor event, this one launched from genuinely La Niña-ish conditions in January.<br>Of course, a multi-model median can hide a lot of disagreement, so it is worth looking at where each individual model puts the peak. The figure below shows the distribution of member peaks across all 14 models.

Peak 2026 Niño 3.4 forecast: model-weighted histogram of each ensemble member’s July-December 2026 maximum (top) and per-model medians with 10-90% member ranges (bottom).<br>Every single model’s median peak lands at very strong (”super”) El Niño intensity, and all but one (JAMSTEC’s SINTEX-F, at 2.2C) put their median above the 2015-16 record. Model agreement this strong is unusual, though I’d note that agreement is not the same thing as skill as I discuss later on.<br>Long-time readers may recall that in a warming world, the raw Niño 3.4 anomaly risks conflating El Niño with the broader ocean warming trend. NOAA’s answer is the relative ONI (RONI), which subtracts the tropical-mean SST anomaly to isolate the ENSO signal. In RONI terms the record holder is actually 1982-83 (a peak monthly value of 2.69C), not 2015-16. However, even using RONI the multi-model median in 11 of the 14 models shows a record event.

As above, but for the relative Niño 3.4 index (RONI): Niño 3.4 anomaly minus the 20S-20N tropical-mean anomaly, with the L’Heureux et al. (2024) variance-restoration scaling applied. The record event in RONI terms is 1982-83 (a peak monthly value of 2.69C).<br>Putting the two together: models give a ~91% chance of a record peak in Niño 3.4 terms and ~77% in RONI terms this year. Whichever way you slice the index, the forecast says the same thing: this is more likely than not to be the strongest El Niño ever observed.<br>So how did we get here? The...