The overwhelming heat of these past few days in Europe has no historical precedent that matches its intensity, duration, extent, and timing. It may seem simple for some to call it “global warming” and for others “the summer heat,” but the reality is complicated. Although it has long been impossible for anyone with even a basic education to ignore that climate change must be behind it (and, of course, the scientific evidence for this change is now irrefutable), there are details we still do not know. Not because we don’t know which physical laws govern the climate (laws that, unlike human laws, we will never have a say in, because they are expressed mathematically and you can’t make two plus two equal five), but because understanding their ultimate consequences is devilishly complicated.
Some equations are relatively simple to formulate and solve, such as the Boltzmann or Wien equations, but others, such as the Navier-Stokes equations, are a nightmare because they must be solved for every liter of air in the atmosphere or water in the ocean… as well as for the 26 liters surrounding that liter, and the results for each liter affect the others and vice versa. Only with large computational models run on the most powerful supercomputers—and by simplifying the atmosphere and ocean into a puzzle with pieces kilometers across—can we arrive at reasonable approximations, which don’t last very long anyway.
However, we can see the major trends. Scientists may disagree on some details, but not on the essentials—namely, that there is an excess of energy in the atmosphere-ocean system that is leading the planet toward a different equilibrium than the one we had before. We are gaining a better understanding of this equilibrium as we obtain more data better models, and the various models are becoming increasingly similar to one another.
One model concerns us greatly is that of ocean water temperature. We know that the surface is warming, and we have a general idea of the consequences of this; after all, major ocean currents depend on temperature distribution and wind circulation, which, in turn, also depend on temperature. The atmosphere and the ocean exchange heat, and both absorb solar radiation. One consequence of this interaction is the El Niño Southern Oscillation (ENSO), the Southern Oscillation, or simply “El Niño,” which begins in the tropical Pacific during some northern winters. It is a warming of the ocean’s surface that occurs in some years and completely alters the patron saint atmospheric circulation and rainfall (which side of the Pacific receives rain: normally Asia, but during El Niño, rainfall shifts toward the Americas). And it rains more: the warm water evaporates more, carrying away more energy, and creates more intense typhoons. It also has many other characteristics: for example, the cold waters that normally rise from the depths along the coast of Chile and Peru—and which fertilize the surface—remain at greater depths. Plankton grows much less, and the fish (and the fishermen) have nothing to eat.
El Niño occurs with some regularity but does not follow a known pattern. There are years when it occurs and others when it does not. A few months in advance, we can predict it reliably. In early June, the World Meteorological Organization (WMO) reported that it is very likely (90%) that a strong El Niño event will occur this year, and this week the probability has risen to 96%. The problem is that we have no idea whether there will be another one next year—or the year after that. I wish we could do better—but it’s not yet possible for three reasons. First, we don’t have all the underlying laws figured out—there are mechanisms we still don’t understand. Second, some of these laws follow the principles of chaotic physics: a tiny initial change leads to a massive final outcome. And third, when El Niño strikes, it doesn’t just change the climate in the Pacific— it affects the entire planet, which in turn affects ENSO itself, even months (or years) later. Yes, Europe—and Spain—can also be affected by El Niño.
But despite what you sometimes hear on social media or in elevators, it’s difficult to definitively link these hot days in Europe to ENSO, because ENSO is particularly evident during certain winters—and is interspersed with the opposite phenomenon, La Niña, which is an anomalous cooling. Based on past episodes, we do believe that El Niño appears to amplify climate patterns. And that would also apply to the European climate. Models show that when El Niño is intense (like the one we’re almost certain we’re going to have), the jet stream—which brings us the storm fronts that enter through Galicia (and makes flying back from North America take nearly two hours less than flying there)—appears to be stronger and more stable. This should mean intense winter rains alternating with dry periods—the anticyclones that form between two storms—unless El Niño is exceptionally intense. In that case, the heat “stolen” from the water and transferred to the atmosphere would spread to a larger portion of the planet (almost all of it, in fact), and the result—in Europe as well—would be a reversal of the guideline: an increasingly mild winter and an unusually warm spring, likely punctuated by more torrential rains.
Even so, we data fully understand all the mechanisms linking ENSO to the climate—or, more precisely, to climate change. The data . Much more research even more powerful models are needed to understand this. To say with certainty that the recent heat is due to El Niño is almost as certain as saying it is due to La Niña, which is the opposite phenomenon. Without a clear and solid causal relationship, we scientists can only point to the coincidences and try to follow the thread. One such coincidence is that the frequency of El Niño events has been increasing, as have the frequency and intensity of hurricanes and episodes of extreme heat in Europe. Another is that exceptionally intense El Niño events have coincided (though not always) with exceptionally anomalous weather patterns.
Coincidence or correlation? Unlike some politicians or talk show hosts, what we scientists can say with absolute certainty—for now—is that “well, we’ll see.”
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Arturo H. Ariño
researcher from Biodiversity and Environment Institute of the University of Navarra
30.06.2026
