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The Pacific Seesaw · The Climate Translation

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Most of the time, we talk about climate as a slow long-term trend, but every few years
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something different happens.
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The Pacific Ocean, the largest feature on the planet, shifts its weight from one side
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to the other.
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That shift is called the ENSO, the El Nino Southern Oscillation, and it's one of the
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closest thing Earth has to a heartbeat.
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Today we're going to take apart this natural phenomena and look at how changes in ocean
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temperatures near South America can help trigger droughts in Australia, floods in California,
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and weather extremes across the globe.
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We'll separate the myths from the mechanics, explain what ENSO can and can't do, and explore
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how climate change may be putting this natural cycle under added strain.
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Welcome to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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To understand how the El Nino Southern Oscillation works, we need to start with how the tropical
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Pacific normally functions.
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In an average year, strong trade winds blow steadily from east to west along the equator.
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These winds push the warm surface water away from South America and towards Indonesia and
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Australia.
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Another time that warm water actually piles up in the western Pacific, sometimes by more
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than a foot, that pile of warm water is important.
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Warm water heats the air above it, causing air to rise and create low pressure.
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Cooler water does the opposite.
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So as warm water builds up in the west, air rises there.
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It then flows eastward in the atmosphere and then sinks over the eastern Pacific, and
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then flows back west along the surface.
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That loop is called a walker circulation.
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At the surface, this circulation reinforces the trade winds, and along the coast of South
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America, those winds pull surface water away from the shore, allowing cold, nutrient-rich
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water to rise up from the deep.
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This process, called upwelling, supports some of the most productive fisheries on Earth.
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Now, that's the baseline, that's normal.
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ENSO happens when the system gets knocked out of balance.
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During El Nino, the trade winds weaken, sometimes dramatically.
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When that happens, the warm water that's piled up in the western Pacific is no longer held
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in place.
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Gravity takes over, and that warm water sloshes back east towards South America.
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As it spreads out, the eastern Pacific warms.
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The cold, upwelling shuts down, and the entire pressure pattern across the Pacific shifts.
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The atmosphere responds, almost immediately.
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Rainfall patterns move east.
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Regions that are normally wet can dry out.
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Places that are dry can see flooding, and because the Pacific is so large, those changes
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ripple outward into weather patterns across most of the globe.
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Now, La Niña is the exact opposite.
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The trade winds just don't strengthen, they go into overdrive.
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Warm water is pushed even farther west, cold, upwelling in the east intensifies, and the
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temperature contrast across the Pacific becomes stronger than normal.
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That supercharged contrast locks the walker circulation into a more intense version of
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its usual pattern, often bringing cooler global temperatures and a different set of climate
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impacts worldwide.
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So it's the same system, just different settings.
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A useful way to think about ENSO is a giant bathtub.
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In a normal year, it's like your hands are pushing water towards one end.
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That's the trade winds doing their job.
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During El Niño, your hands stop pushing, and the water sloshes back the other way.
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During La Niña, you push harder than usual, exaggerating the imbalance.
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The tub hasn't changed, the water hasn't changed.
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What's changed is the force applied to the system, and that's a key point.
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ENSO isn't a storm, it's not a switch that flips on and off, it's a natural oscillation,
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a back and forth movement that's coupled to the ocean atmospheric system.
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Understanding that seesaw is the key to understanding everything that follows, including why ENSO
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has global effects, why its impacts aren't the same everywhere, and why climate change
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complicates the picture without directly causing El Niño or La Niña.
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The El Niño Southern Oscillation has a direct impact on the ocean's food delivery service.
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In the eastern Pacific, especially off the coast of Peru, the normal state of the ocean
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is surprisingly generous.
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Strong trade winds push surface water away from the coast, and the cold water rises up
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from the deep to replace it.
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That rising water is packed with nutrients, things like nitrates, phosphates and iron, eroded
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from rock and stored in the deep ocean.
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When they reach the sunlight, microscopic plants called phytoplankton explode in number.
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That plankton feeds anchovies, anchovies feed larger fish, birds, seals, and whales feed
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on all of it.
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It's one of the most productive marine ecosystems on earth.
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That's the East Pacific feast.
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In my oceanography classes, this is usually when a student asks, well, if the water is colder,
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why is it better for life?
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It's because cold water from the depths is old water.
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It's been sitting in the dark collecting nutrients for decades or even centuries.
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Warm water by contrast is often nutrient poor, it's been stripped clean by biology already.
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It's not the temperature that matters as much as the nutrients.
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During El Niño, when warm water sloshes eastward, that nutrient conveyor belt breaks down.
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The warm surface water thickens and acts like a lid to the ocean.
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The upwelling slows or shuts off entirely.
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The nutrients can't reach the surface sunlight, phytoplankton production crashes, and the
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entire food web begins to unravel.
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Anchovies either migrate or die off, seabirds abandon nesting sites or starve in some cases.
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Fisheries can collapse even within months.
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So can't the fish just eat something else?
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I might be asked?
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Well, not easily.
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Even food webs are efficient, but fragile.
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When the base collapses, there's usually nothing to replace it very quickly.
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You can't really skip steps in an ecosystem.
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But not all marine life loses during El Niño.
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As warm water spreads poleward, species that prefer more tropical conditions can follow it.
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Fish like mahi mahi tuna and even some sharks suddenly appear far outside their usual ranges.
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During especially strong El Niño events, you can even find some tropical fish as far
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north as San Francisco.
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Of course, this leads to another common question.
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Does that mean climate change is happening there?
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Well, not necessarily, and that's an important thing to note.
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ENSO doesn't create new species or new behaviors.
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It rearranges where existing species can't survive temporarily.
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When conditions shift back, many of those species retreat.
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But there's a catch.
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Repeated or extreme ENSO events can stress ecosystems faster than they can recover.
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Coral reefs can have more bleaching events.
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Kelp forests can weaken.
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Species that rely on stable conditions struggle to rebound before the next disruption arrives.
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And that leads to one last important question.
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If this keeps happening, does temporary start to become permanent?
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And that question sits at the edge of modern climate science.
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ENSO has always been part of the Earth's system, as far as we can tell.
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But as the background ocean warms, the impacts of each swing can become more damaging.
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Not because anything here is new, but because the system it's operating in is changing.
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The ocean doesn't respond to ENSO once, it remembers.
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And understanding that memory made up of the biological, the chemical, and the physical
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processes is key to understanding why ENSO matters far beyond the Pacific Ocean.
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So how does a change in ocean temperature in the middle of the Pacific end up affecting
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rainfall in Kansas, snowfall in California, or droughts in Australia?
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The answer starts with the jet stream.
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High above our head, the jet stream is a concentrated corridor of air that flows from the west to
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the east.
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It helps steer storms, control temperature contrasts, and decide where rain and snow tend to fall.
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And the jet stream responds to where heat is released in the atmosphere.
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And that's where ENSO comes in.
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Think of the jet stream like a fast-moving river.
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Under normal conditions, it follows a familiar path.
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But ENSO is like dropping a massive boulder into that river.
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The atmosphere doesn't ignore it, it has to flow around it.
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It creates bends and waves and ripples that travel far downstream.
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During El Nino, warm water spreads east across the Pacific.
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The warm water heats the air above it, causing more air to rise in places where it normally
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doesn't.
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That rising air changes pressure patterns, and pushes that fast-moving jet stream into
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a new configuration.
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During La Niña, the opposite happens.
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Heat stays farther west, and the jet stream responds in a different way.
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That process is called teleconnection.
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It's a fancy word for something that happens here that affects the weather far away.
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So why doesn't this just stay over the ocean, or around the ocean area?
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It's because the atmosphere is fluid and connected.
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We live on a planet where everything's connected.
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Once you change where the large amounts of heat enter this system, the entire circulation
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across the entire globe adjusts.
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In the United States, El Nino often shifts the jet stream southward.
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That makes the southern U.S. cooler and wetter, especially in winter, while the northern
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U.S. can end up warmer and drier than average.
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California is more likely to see heavy rain events, though not every El Nino guarantees them.
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Meanwhile, in parts of Southeast Asia and Australia, El Nino can suppress rainfall, increasing
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the risk of drought, wildfires, and crop stress.
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La Niña tends to flip many of those patterns, increasing the rainfall in the western Pacific
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and shifting storm tracks northward in North America.
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So does El Nino cause the storms?
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No.
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ENSO doesn't create individual storms.
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It changes the background conditions that storms move through and either grow them or
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suppress them.
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It's where the loaded dice analogy happens.
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ENSO doesn't roll the dice for the atmosphere, it loads them.
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During El Nino and La Niña, certain outcomes become more likely.
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Nothing is guaranteed, though.
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You can still have a quiet El Nino winter or an intense La Niña season with few extremes
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in a given location.
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When it comes right down to it, climate is complicated.
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It's about probability, not certainty.
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One of the biggest misconceptions is that ENSO can explain a lot of things.
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Not every drought, flood, or heat wave can be blamed on La Niña or El Nino.
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Weather is influenced by overlapping systems from Arctic oscillations to local sea surface
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temperatures to random variability.
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Even land-cover differences can affect the weather.
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ENSO is powerful because it tilts the odds across large regions, though.
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Not because it controls the outcome.
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And that's why ENSO is important for seasonal forecasting.
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It doesn't tell us exactly what will happen, but it tells us in probabilistic terms what's
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more likely.
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Understanding that difference helps prevent both over-hype and misplaced blame.
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So if ENSO is always been part of the Earth's system, as far as we can tell, what happens
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when the background climate it's operating in begins to change.
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Yes, ENSO has been part of the Earth's climate system for a very long time.
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It's a natural oscillation driven by ocean heat, winds, and pressure differences across
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the Pacific Ocean.
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Climate change didn't create it, but human-induced climate change does change the conditions
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ENSO operates in.
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Over the last several years, new research has begun to converge on a worrying problem.
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Studies published in 2025 and 2026 suggest the Pacific may be shifting towards what scientists
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sometimes call climate whiplash, larger, faster swings between very strong El Niño and
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very strong La Niña events.
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It's important to point out that not every study agrees on the details, but they all point
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in the same general direction.
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And the reason comes back to something we've already talked about, that stored heat.
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The oceans absorb more than 90% of the excess heat trapped by the greenhouse gases.
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We are an ocean world, after all.
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That means ENSO is now operating on top of a much warmer background than it did just
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even a few decades ago.
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Think of it this way.
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If ENSO is a sea saw, climate change is raising the floor underneath that middle part that
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holds the plank, which allows both sides to rise and lower more.
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So when an El Niño begins today, it's starting from a higher temperature baseline.
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The warm water that sloshes east isn't just warmer relative to normal, it's warmer than
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absolute terms.
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That means a moderate El Niño can produce impacts that resemble a strong El Niño from
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40 years ago.
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It's not because ENSO itself has changed category, but because the system is interacting
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with already hotter conditions.
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So does that mean every El Niño will be extreme now?
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Absolutely not.
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ENSO is variable.
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Some events will still be weak.
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Some years will be quiet.
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The cycle hasn't become a metronome, but the risks are growing.
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When ENSO does swing strongly, it now has more energy to work with, more ocean heat to
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release into the atmosphere, more moisture to fuel storms, and higher background temperatures
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to amplify heat waves and droughts.
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Another key insight from research is that stronger swings can arrive closer together.
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In the past, a strong El Niño might be followed by several calmer years, but as the ocean
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stores more heat, the system can be primed to rebound sharply, flipping from El Niño
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to La Niña as fast as a year.
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That's where the idea of climate whiplash comes from.
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Wet years followed by dry years, floods followed by droughts, heat waves stacked on top of
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already warm conditions.
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ENSO is shifting the odds, but the stakes attached to those odds are also rising.
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And this is where a misconception needs clearing up, ENSO is not causing climate change.
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ENSO is not changing anything about greenhouse warming.
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It's not an excuse to dismiss long-term trends.
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A weak El Niño, or a strong La Niña, is not an excuse to say that humans are not affecting
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the climate.
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You can often hear people say, well, that's just an El Niño, or that's just a La Niña,
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because if it explains everything, it doesn't.
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ENSO explains the timing, climate change, explains the severity and the direction.
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ENSO tells us when and where extremes are likely.
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Climate change stacks the deck and determines how intense and extreme they can become once
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they happen.
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They're not competing explanations, they're layered on top of each other in sometimes
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complex ways.
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And that complexity is a concern, because a climate system that swings naturally becomes
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more dangerous when it's operating an overdrive.
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Not because anything here is new, but because the margins, or for recovery, are smaller.
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And that's the takeaway I hope you get here, ENSO isn't broken.
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It's not really changed that much.
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It's being stressed, and it's reacting to that stress.
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ENSO reminds us that the Earth isn't a collection of separate parts.
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It's a single interconnected system.
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Heat stored in the Pacific doesn't stay in the Pacific.
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It eventually reshapes winds, storms, ecosystems, and daily life far from the ocean.
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Understanding ENSO doesn't help us control the weather, but it does give us something
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just as important a context.
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It helps us to see the difference between short-term swings and long-term change between
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natural rhythms and the added strain of a warming world.
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As climate change raises the background temperature of our planet.
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Scientists are focused on the data.
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ENSO's natural heartbeat is growing louder, and learning to listen to it carefully is
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one of the best tools we have for preparing, rather than reacting.
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I'm Dr. Mac, and this has been the climate translation.
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If you have a question about the climate that you've been too afraid to ask, or if you
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have a differing opinion, please let me hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.