El Niño and La Niña shape rainfall, drought, food security, and humanitarian planning across the globe. They are the warm (El Niño) and cool (La Niña) phases of a natural climate pattern across the tropical Pacific known as the El Niño-Southern Oscillation, or “ENSO” for short. But just how far ahead can we really predict ENSO? 

A new study, by three generations of scientists, offers one of the clearest answers yet: not as far as we might hope.

Using a century‑long computer simulation of the climate, an international research team has shown that short‑lived atmospheric “chatter” generates a surprisingly large response in ENSO.

Unpredictable changes to the weather over days to weeks, such as chaotic winds and rapid temperature variations, shapes the timing and size of El Niño and La Niña events far more often than the slower, more predictable dynamics of the atmosphere and its connections with the ocean.

While we have made many advances in climate prediction, weather forecasts are limited by fundamental uncertainties. Definitive predictions can only be made a few weeks in advance, and recognising where weather fluctuations have a significant impact on larger climate processes is key to understanding what that means for our ability to model future climate conditions.

Dr Ioana Colfescu, research scientist at NCAS and the University of St Andrews, explains:

“Atmospheric weather noise accounts for roughly 70% of ENSO variance in the climate model. That number is striking not only for its size, but for its implications. If most ENSO variability is driven by something fundamentally unpredictable beyond a few weeks, then the forecasting of the warm El Niño and cool La Niña phases will inherit that limit.

“No matter how much we improve our models, increase our resolution, or expand our observing networks, that noise cannot be forecast – and because it is driving so much of ENSO, it places a hard ceiling on predictability that is built into the physics of the system itself. Better models will help us get closer to that ceiling, but they cannot break through it. Knowing where the ceiling is, and why, is itself a form of progress.”

For policymakers, aid organisations, and farmers who rely on seasonal guidance, this is some important clarification. Knowing where the predictability limit sits, and why, helps with planning and investment.

Beyond the science, this research also tells a deeply human story. Ioana shares: “This work was conducted by a trio of researchers spanning three scientific generations – my former PhD supervisor Edwin Schneider, my early‑career mentor Emma Carey‑Prieto, and myself. Our project was able to happen because of over 10 years of collaboration, communication, and curiosity.”

She adds: “Ultimately, the study highlights two connected conclusions: ENSO variability is strongly shaped by inherently unpredictable atmospheric noise, and our understanding of the climate system advances through sustained collaboration across generations of scientists.”