The majority of the world’s weather is actually determined in a strip of ocean that runs along the equator, between the islands of the central Pacific and the coast of Peru. A belt of cool, blue water hugs the South American coast on a typical year’s satellite map of the area, while warmer water pools thousands of miles west near Indonesia and the Philippines. By default, that pattern is used. For the most of human history, it has been the default. When it cracks, which happens sporadically every two to seven years, the effects spread like unrelated disasters from the ground in any one nation. They’re not. They are El Niño’s distinguishing feature.
Contrary to what the headlines frequently imply, the fundamental mechanics are straightforward. Strong trade winds often blow around the equator from east to west, forcing warm surface water toward Asia and allowing colder, nutrient-rich water to rise near the coast of South America. The anchovy fisheries off Peru and Ecuador are fed by the upwelling, which is one of the reasons Peruvian fisherman observed the pattern breaking centuries ago. Because the disturbance frequently occurred around Christmas, the event was given the Spanish moniker El Niño, or “the boy,” which alludes to the Christ child. The naming was informal. Three hundred more years were needed to complete the science.
The trade winds diminish or, in severe episodes, completely change direction during an El Niño event. The western Pacific’s accumulated warm water starts to slop back east. After that, the exceptionally warm water pool remains in the eastern and central equatorial Pacific for several months. Like a radiator the size of a continent turned on beneath the jet stream, that heated water discharges massive amounts of heat into the atmosphere. The jet stream moves. The tracks of storms move. California receives rain that ought to have dropped in Indonesia. Rainfall that is supposed to fall in northern Brazil instead falls in Peru. The entire atmospheric circulation that disperses weather over the world is forced to deviate from its typical pattern.
The consequences are dispersed unevenly in ways that frequently seem illogical. During a severe El Niño, the southern United States, especially near the Gulf Coast, typically experiences colder and wetter winters. Conditions are drier and warmer in the northern United States and Canada. Devastating floods frequently strike the western coast of South America, especially Peru and Ecuador, while severe droughts can occur in regions of Colombia and the interior of Brazil.
Due to their generally lower rainfall, Australia and Southeast Asia have historically experienced longer droughts and more severe wildfire seasons. While Southern Africa frequently has dry spells, Eastern Africa frequently experiences wetter circumstances. These are not assurances; they are tendencies. Every El Niño is unique, and the intensity of the phenomenon is just as important as its existence.
As the climate has warmed, it has become more difficult to overlook the global temperature dimension. Because heat that was stored in the western Pacific is released into the atmosphere, El Niño years are typically exceptionally hot worldwide. For a considerable amount of time, 2016—an El Niño year—was the warmest year ever recorded. That record was broken in 2023 and 2024, during the most recent powerful El Niño. The pattern has taken on the role of an amplifier when applied to a globe that is already warming. Scientists are keeping an eye on how much El Niño contributes to a baseline that is already greater than it has ever been in human history. It’s uncomfortable math.
Even if many who check their local weather app may not always feel that way, the forecasting job is quite excellent. Together with sister organizations worldwide, the NOAA Climate Prediction Center has established a network of satellite instruments, ocean buoys, and atmospheric models that can identify early indicators of an El Niño months before its surface effects become apparent. Agricultural commodities dealers, water utility managers, insurance underwriters, and humanitarian organizations now consider the ENSO Diagnostic Discussion, a monthly bulletin published by NOAA, to be nearly mandatory reading. People whose jobs depend on predicting whether the Pacific is going to restart the cycle six to nine months in advance make up a quiet economy.
As I watch this unfold over several cycles, I find it fascinating how blatantly El Niño highlights the artificiality of national borders in terms of weather. In common terms, a flood in southern California and a drought in northeastern Brazil are not the same thing. They are to a climatologist. Despite being separated by a continent and thousands of miles, they are two sides of the same atmospheric rearrangement because the heat had to go somewhere. When you sit with climate science for a time, one of the things that makes it truly odd and lovely is that kind of long-distance physical connection.
Scientists are still figuring out how this relates to climate change. There is no conclusive proof that warming has increased the frequency of El Niño episodes. There is growing evidence that when they do happen, their consequences might be more severe because the underlying ocean is already warmer and because decades of greenhouse gas buildup have changed the atmospheric circulation. Stronger El Niños may become more frequent in the future, according to some study. There is less certainty in other models. Seeing this develop is one of those instances where the scientific community is being open about its own uncertainties in a way that isn’t often evident in news reports.