El Niño is one of those phenomena everyone has heard of. It shows up every few years, warms the Pacific Ocean, shifts rainfall patterns, bringing drought to some regions and floods to others. It has almost become a recurring character in the global climate narrative.
And yet, beneath this apparent familiarity lies a problem: El Niño is far less understood than it seems.
Not for lack of data or research, quite the opposite. It is one of the most observed, modeled, and studied phenomena in modern climatology. But this very abundance of knowledge has revealed a more complex reality:
there is no single El Niño and, above all, there is no simple way to predict it.
In this article, I’ve brought together some of the most interesting recent research to explain, in accessible terms, what El Niño is and why, despite everything, we still only partially understand it.
The most common definition is straightforward: El Niño is an abnormal warming of surface waters in the equatorial Pacific Ocean.
But even here, a first crack appears. Where exactly do we measure this warming? And compared to what “normal”?
Scientists use different indices (such as Niño-3.4 or ONI), each based on slightly different regions and thresholds. The result is that the same event can be classified differently depending on the system used.
In recent years, the issue has become even more complex: global warming is shifting what we consider “normal.” For this reason, new indicators have been introduced that compare Pacific conditions with the broader tropical system, attempting to correct for a moving baseline.
The implication is significant, yet often overlooked:
El Niño is not just a natural phenomenon, it is also shaped by how we choose to measure it.
Even if we know when an El Niño begins, a crucial question remains unanswered: what kind of El Niño will it be?
For years, the main distinction was thought to be intensity, stronger or weaker events. Today we know it’s not that simple. Recent research shows that El Niño can evolve in different ways:
This difference is not trivial, it completely changes the global climate impacts. And here comes the most important insight:
The fate of an El Niño is decided much earlier than we once thought.
Not at its peak, but already during its initial development phase, when the event is still forming.
In practice, small differences at the beginning - intensity, heat distribution, interactions with other ocean basins - determine which path the system will follow.
This fundamentally changes our perspective:
We are not observing a phenomenon that simply grows and fades.
We are observing a system that, from the outset, can take different trajectories.
If El Niño is difficult to define and classify, its effects are anything but abstract.
As Pacific waters warm, winds shift, ocean currents change, and rainfall patterns are disrupted. But these changes are not uniform, they translate into highly specific local impacts.
In some regions: rainfall and flooding increase, in others droughts and wildfires intensify.
In the oceans, the effects can be even more profound. Surface warming reduces the upwelling of cold, nutrient-rich waters, triggering cascading consequences:
In this sense, El Niño is not just a climate anomaly:
it is a force that reorganizes ecological balances.
And this leads to another important implication: if there are different types of El Niño, there are also different types of impact.
At this point, one might expect that with all this knowledge, El Niño would be precisely predictable. It is not.
Climate models are now quite good at estimating whether an event will develop. But they struggle much more to determine:
One of the main challenges is known as the spring predictability barrier—a time of year when the climate system becomes particularly unstable and difficult to interpret. Just when we most need clarity, forecasts become less reliable.
There is also a deeper, structural limitation:
if multiple trajectories are possible, prediction cannot yield a single outcome.
It is not about guessing one result, but about estimating a range of possibilities.
This brings us to a final, often overlooked issue: how we talk about El Niño.
In public discourse, the phenomenon is often reduced to simple categories: eak vs. strong or the headline-friendly "super El Nino".
These labels work well in the media, but they are scientifically limited. Saying that an El Niño will be “very strong” does not tell us:
In other words:
communication simplifies a phenomenon that is, by nature, not simple.
And this creates a gap between what science understands and what the public perceives.
In the end, El Niño confronts us with an interesting contradiction.
On one hand:
On the other:
The result is this:
El Niño is one of the most studied climate phenomena in the world—
yet also one of the least understood in its concrete manifestation.
And perhaps this is the most important takeaway.
Not because science is failing, but because the system we are trying to describe is simply more complex than we would like it to be.
Chen, J. et al. (2025). Pantropical climate interactions and CP El Niño decay. Atmospheric and Oceanic Science Letters.
Observational studies on local impacts (La Paz Bay, 2015–2016).
Witze, A. (2026). Are we really headed for a ‘super’ El Niño? Nature.
ENSO literature on definitions and metrics (NOAA, ERSST, ONI, RONI).