In June 2026, the National Oceanic and Atmospheric Administration officially confirmed the return of El Niño, forecasting a strengthening of the phenomenon through the winter of 2026 to 2027, and estimating a 63 per cent likelihood that the event would reach a historically significant intensity, ranking among the strongest episodes recorded since 1950. The announcement has sharpened a dispute among climate scientists that has persisted for years: whether rising greenhouse gas emissions are altering the nature of El Niño itself, or merely the conditions in which it occurs.

El Niño is driven by a weakening of the Pacific trade winds, which allows warm surface water to spread eastward across the equatorial Pacific, disrupting rainfall and temperature patterns across much of the globe. What remains contested is whether human-induced warming is changing the frequency and severity of those events, or whether the cycle's behaviour falls within the range of natural variability observed across centuries of records.

Friederike Otto, a climate scientist at Imperial College London and World Weather Attribution, has argued that climate change will likely play a larger role in this year's extreme weather than El Niño itself, pointing to more than a hundred analyses that have controlled for the effects of the El Niño-Southern Oscillation. According to Otto, the reason El Niño is "so dramatic is not the event itself and whether it's a Super El Niño or not, but that it is happening in a dramatically changing climate." Put another way, the increased baseline against which the cycle is currently functioning is more concerning than the cycle's inherent severity.

Global temperatures are already running over 1.4 degrees Celsius above pre-industrial levels, and a strong El Niño layered on top of that baseline takes the climate system somewhere it has not been in modern human history. Some climate models show global temperatures briefly exceeding 2.0 degrees Celsius above pre-industrial levels, driven by the potential super El Niño combined with ongoing global warming which would be the first time in recorded history the planet reaches a temperature anomaly this high.

Those arguing that warming is actively reshaping the cycle point to ocean heat content as a driver. Paleoclimate proxy data from coral fossils and tree rings suggests that ENSO variability intensified by around 25 per cent during the latter part of the 20th century compared to pre-industrial times, and a growing number of researchers now conclude that human-caused warming is at least partly responsible for changes in ENSO variability since the 1960s. Research published in Nature Climate Change found that newer climate models, those participating in the sixth phase of the Coupled Model Intercomparison Project, show a robust increase in century-long ENSO sea surface temperature variability under four IPCC emission scenarios when comparing the 20th and 21st centuries, a finding the researchers argue was not adequately reflected in the IPCC's own sixth assessment report.

Sceptics of that position point in a different direction. Paleoclimate proxy evidence from coral, tree rings and sediment cores shows that throughout the Holocene, the last 11,700 years, ENSO has displayed all sorts of different patterns and amplitudes. There is no conclusive proof that the modifications after 1950 are out of the ordinary. 

Climate model simulations that do not include rising greenhouse gases produce similarly large variations in ENSO behaviour over long periods of time. The attribution problem is compounded by the relatively short instrumental record, which makes it difficult to distinguish a genuine human-driven trend from the system's natural multi-decadal swings.

The IPCC's sixth assessment report stated medium confidence that both ENSO amplitude and the frequency of high-magnitude events since 1950 are higher than over the period from 1850, and possibly as far back as 1400, while also noting that determining whether this reflects human-caused warming or inherent variability is not straightforward, partly because sea surface temperature records before 1950 are sparse and unreliable. A further complication is the possibility, advanced by some researchers, that uniform global warming across the Pacific could actually stabilise temperature gradients and constrain the cycle rather than amplify it.

The stakes of the debate extend beyond academic disagreement. A December 2025 study in Nature Communications found that super El Niño events significantly increase the likelihood of abrupt, persistent transitions in temperature, sea surface conditions and soil moisture that can endure for years after the event has faded and that under global warming scenarios, this effect would be greatly amplified. The UN Food and Agriculture Organisation and the World Food Programme have already launched a joint anticipatory action appeal seeking $202 million to help nearly 8.8 million people prepare for expected El Niño impacts.

Meteorological agencies are treating the current event as an opportunity to test the competing hypotheses in real time. The outcome matters for how infrastructure is designed, how insurance risk is priced, and how far in advance governments in vulnerable regions can act. The answers are not yet settled, and the Pacific is not waiting.