The Pacific Seesaw

Introduction

Most of the time, we talk about climate as a slow, long-term trend. But every few years, something very different happens. The Pacific Ocean, the largest feature on our planet, shifts its weight from one side to the other. That shift is called ENSO, the El Niño–Southern Oscillation, and it is one of the closest things Earth has to a heartbeat.

Today, we are going to take apart this natural phenomenon. We will look at how a change in ocean temperatures near South America can help trigger droughts in Australia, floods in California, and weather extremes across the globe. We will separate the myths from the mechanics, explain what ENSO can and cannot do, and explore how climate change may be putting this natural cycle under added strain. Welcome back to the podcast. I'm Dr. Mac, and this is The Climate Translation.

The Seesaw

To understand the El Niño–Southern Oscillation, we need to start with how the tropical Pacific normally works. In an average year, strong trade winds blow steadily from east to west along the equator. These winds push warm surface water away from South America and toward Indonesia and Australia. Over time, that warm water actually piles up in the western Pacific, sometimes by more than a foot. That pile of warm water matters.

Warm water heats the air above it, causing air to rise and create low pressure, while cooler water does the opposite. As warm water builds up in the west, air rises there, flows eastward high in the atmosphere, sinks over the eastern Pacific, and then flows back west along the surface. That entire loop is called the Walker Circulation. At the surface, this circulation reinforces the trade winds. Along the coast of South America, those winds pull surface water away from the shore, allowing cold, nutrient-rich water to rise up from the deep. This process, called upwelling, supports some of the most productive fisheries on Earth. That is the baseline, and that is normal.

ENSO happens when that system gets knocked out of balance. During El Niño, the trade winds weaken, sometimes dramatically. When that happens, the warm water piled up in the western Pacific is no longer held in place. Gravity takes over, and that warm water sloshes back east toward South America. As it spreads out, the eastern Pacific warms, the cold upwelling shuts down, and the entire pressure pattern across the Pacific shifts. The atmosphere responds almost immediately. Rainfall patterns move east. Regions that are normally wet can dry out, and places that are usually dry can see flooding. Because the Pacific is so large, those changes ripple outward into weather patterns across much of the globe.

La Niña is the opposite extreme. The trade winds do not just strengthen; they can go into overdrive. Warm water is pushed even farther west, cold upwelling in the east intensifies, and the temperature contrast across the Pacific becomes stronger than normal. That supercharged contrast locks the Walker Circulation into a more intense version of its usual pattern, often bringing cooler global temperatures and a different set of climate impacts worldwide. It is the same system with different settings.

A useful way to think about ENSO is as a giant bathtub. In a normal year, the water is already pushed toward one end by the trade winds doing their job. During El Niño, your hands stop pushing, and the water sloshes back the other way. During La Niña, you push harder than usual, exaggerating the imbalance. The tub has not changed, and the water has not changed. What has changed is the force applied to the system. ENSO is not a storm, and it is not a switch that flips on and off. It is a natural oscillation, a back-and-forth movement in a coupled ocean-atmosphere system. Understanding that seesaw is the key to understanding everything that follows, including why ENSO has global effects, why its impacts are not the same everywhere, and why climate change complicates the picture without directly causing El Niño or La Niña.

The Oceans and Ocean Life

The El Niño–Southern Oscillation has a direct impact on the ocean's food delivery service. In the eastern Pacific, especially off the coast of Peru, the normal state of the ocean is surprisingly generous. Strong trade winds push surface water away from the coast, and cold water rises up from the deep to replace it. That rising water is packed with nutrients, such as nitrates, phosphates, and iron, eroded from rock and stored in the deep ocean. When they reach sunlight, microscopic plants called phytoplankton explode in number. That plankton feeds anchovies, anchovies feed larger fish, and birds, seals, and whales feed on all of it. It is one of the most productive marine ecosystems on Earth: the East Pacific feast.

In my oceanography courses, this is usually when a student asks: if the water is colder, why is it better for life? It is because cold water from depth is old water that has been sitting in the dark, collecting nutrients for decades or centuries. Warm surface water, by contrast, is often nutrient-poor because it has been stripped clean by biology already. Cold does not matter; nutrients do. During El Niño, when warm water sloshes eastward, that nutrient conveyor belt breaks down. The warm surface layer thickens and acts like a lid on the ocean. Upwelling slows or shuts off entirely, nutrients cannot reach the sunlit surface, phytoplankton production crashes, and the entire food web begins to unravel. Anchovies either migrate or die off, seabirds abandon nesting sites or starve, and fisheries collapse, sometimes within months.

I might be asked: can't the fish just eat something else? Not easily. Marine food webs are efficient but fragile. When the base collapses, there is nothing to replace it quickly, because you cannot skip steps in an ecosystem. But not all marine life loses during El Niño. As warm water spreads poleward, species that prefer tropical conditions follow it. Fish like mahi-mahi, tuna, and even some sharks suddenly appear far outside their usual ranges. During strong El Niño events, tropical fish are sometimes caught as far north as San Francisco.

This leads to another common question: does that mean climate change is happening right there? Not necessarily. This is an important thing to note: ENSO does not create new species or new behaviors; it temporarily rearranges where existing species can survive. When conditions shift back, many of those species retreat. But there is a catch. Repeated or extreme ENSO events can stress ecosystems faster than they can recover. Coral reefs bleach, kelp forests weaken, and species that rely on stable conditions struggle to rebound before the next disruption arrives.

This leads to one last, very honest student question: if this keeps happening, does temporary start to become permanent? That question sits right at the edge of modern climate science. ENSO has always been part of Earth's system, but as the background ocean warms, the impacts of each swing can become more damaging, not because ENSO is new, but because the system it is operating in is changing. The ocean does not just respond to ENSO once; it remembers. Understanding that biological, chemical, and physical memory is key to understanding why ENSO matters far beyond the Pacific.

The Boulder in the Stream

So how does a change in ocean temperature in the middle of the Pacific end up affecting rainfall in Kansas, snowfall in California, or droughts in Australia? The answer starts with the jet stream. High above our heads, the jet stream is a concentrated corridor of air that flows from west to east. It helps steer storms, control temperature contrasts, and decide where rain and snow tend to fall. The jet stream responds directly to where heat is released into the atmosphere, and that is where ENSO comes in.

Think of the jet stream like a fast-flowing river. Under normal conditions, it follows a familiar path, but ENSO is like dropping a massive boulder into that river. The atmosphere cannot just ignore it; it has to flow around it. That creates bends, waves, and ripples that travel far downstream. During El Niño, warm water spreads east across the Pacific, heating the air above it and causing more air to rise in places it normally would not. That rising air changes pressure patterns and pushes the jet stream into a new configuration. During La Niña, the opposite happens: heat stays concentrated farther west, and the jet stream responds in a different way. This process is called a teleconnection, which is a term for how something happening in one region affects weather far away.

Why doesn't this just stay over the ocean? It is because the atmosphere is fluid and connected. Once you change where large amounts of heat enter the system, the entire circulation adjusts. In the United States, El Niño often shifts the jet stream southward. That makes the southern United States cooler and wetter, especially in winter, while the northern parts of the country can end up warmer and drier than average. California is more likely to see heavy rain events, though not every El Niño guarantees them. Meanwhile, in parts of Southeast Asia and Australia, El Niño often suppresses rainfall, increasing the risk of drought, wildfires, and crop stress. La Niña tends to flip many of those patterns, increasing rainfall in the western Pacific and shifting storm tracks northward in North America.

Does El Niño cause these storms? The answer is no. ENSO does not create individual storms; it changes the background conditions that storms move through. This is where the loaded dice analogy helps. ENSO does not roll the dice for the atmosphere; it loads them. During El Niño or La Niña, certain outcomes become more likely, but nothing is guaranteed. You can still have a quiet El Niño winter or an intense La Niña season with few extremes in a given location, because climate is about probability rather than certainty.

One of the biggest misconceptions is that ENSO explains everything. Not every flood, drought, or heat wave can be blamed on El Niño or La Niña. Weather is influenced by many overlapping systems, from the Arctic Oscillation to local sea surface temperatures and random variability. ENSO is powerful because it tilts the odds across large regions, not because it controls every outcome. That is why ENSO is so important for seasonal forecasting: it does not tell us exactly what will happen, but it tells us what is more likely. Understanding that difference helps prevent both overhype and misplaced blame. So, if ENSO has always been part of Earth's system, what happens when the background climate it is operating in starts to change?

The Greenhouse Overdrive

ENSO has always been part of Earth's climate system as a natural oscillation driven by ocean heat, winds, and pressure differences across the Pacific. Climate change did not create it, but human-induced climate change does change the conditions ENSO operates in. Over the last several years, new research has begun to converge on a worrying pattern. Studies published in 2025 and 2026 suggest the Pacific may be shifting toward what scientists sometimes call climate whiplash: larger, faster swings between very strong El Niño and very strong La Niña events.

Not every study agrees on the details, but many point in the same direction, and the reason comes back to stored heat. The oceans absorb more than 90 percent of the excess heat trapped by greenhouse gases. That means ENSO is now operating on top of a much warmer background than it did just a few decades ago. Think of it this way: if ENSO is a seesaw, climate change is raising the fulcrum underneath the plank, allowing both sides to swing higher and lower. When an El Niño begins today, it starts from a higher temperature baseline. The warm water that sloshes east is not just warmer relative to normal, it is warmer in absolute terms. That means a moderate El Niño now can produce impacts that resemble a strong El Niño from forty years ago, not because ENSO itself has changed category, but because the system it is interacting with is already hotter.

Does that mean every El Niño will be extreme now? Not necessarily. ENSO is still variable. Some events will be weak, some years will be quiet, and the cycle has not become a metronome. But the tail risks are growing. When ENSO does swing strongly, it now has more energy to work with, including more ocean heat to release into the atmosphere, more moisture to fuel storms, and higher background temperatures to amplify heat waves and droughts. Another key insight from recent research is that stronger swings can arrive closer together. In the past, a strong El Niño might be followed by several calmer years. But as the ocean stores more heat, the system may be primed to rebound more sharply, flipping from El Niño to La Niña faster and harder.

That is where the idea of climate whiplash comes from: wet years followed by dry years, floods followed by droughts, and heat waves stacked on top of already warm conditions. ENSO still shifts the odds, but the stakes attached to those odds are rising. This is where one more misconception needs clearing up: ENSO is not causing climate change, ENSO is not replacing greenhouse warming, and ENSO is not an excuse to dismiss long-term trends. You will sometimes hear people say, "This is just El Niño," as if that explains everything. It does not. ENSO explains timing, while climate change explains direction. ENSO tells us when and where extremes are more likely, whereas climate change determines how intense those extremes can become once they happen. They are not competing explanations, but are layered on top of each other. That complex layering is the real concern, because a climate system that swings naturally becomes more dangerous when it is operating in overdrive. The swings are not new, but the margins for recovery are smaller. That is the takeaway: ENSO is not broken, it is becoming stressed.

Conclusion

ENSO reminds us that Earth is not a collection of separate parts, but a single, interconnected system. Heat stored in the Pacific does not stay in the Pacific. Eventually, it reshapes winds, storms, ecosystems, and daily life far from the ocean itself. Understanding ENSO does not let us control the weather, but it does give us something just as important: context. It helps us see the difference between short-term swings and long-term change, between natural rhythms and the added strain of a warming world.

As climate change raises the background temperature of the planet, ENSO's natural heartbeat does not disappear; it grows louder. Learning to listen to it carefully is one of the best tools we have for preparing rather than reacting.

I'm Dr. Mac. This has been The Climate Translation. If you have a question about the climate that you have been too afraid to ask, or if you have a differing opinion, I want to hear from you. I can use your viewpoints in a future episode. You can reach me at TheClimateTranslation@gmail.com. I'll see you next time.