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The Pacific Pulse · The Climate Translation

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Scientists have predicted that we'll see an average of around 1 to 3 feet of sea level
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rise globally by the end of this century due to climate change.
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But what if I told you that along parts of the Pacific coast, the ocean could temporarily
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rise by several additional inches, and in some locations water levels could run close
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to a foot above what would normally be expected all within a matter of weeks.
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Today we're going to talk about Kelvin waves and how the historic Super El Nino where
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you're experiencing may play havoc along our coastal regions for several months to come.
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Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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When we talk about waves, most people visualize standing on a beach and looking out of the
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water.
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Whether on an ocean or a small body like a lake, water particles react to the energy that
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move through them.
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In most cases, this is due to wind blowing across the surface.
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The wind transfers energy into the water, causing water particles near the surface to move
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in small orbital paths while the wave energy travels forward.
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The result is what we call a wave.
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I like to use this analogy when I'm teaching about this subject in the classroom.
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Imagine you're standing at a football stadium and the crowd begins to react.
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One person stands up and then the person next to them, then the next person, until a wave
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appears to travel all the way around the stadium.
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The people are not running laps around the stadium, only the pattern moves.
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Individually, people are just standing up and sitting down in place.
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Ocean waves work in the similar way.
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The pattern and the energy can move along distance, even though the individual parcels
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of water do not travel the entire distance with the wave.
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We are used to seeing ordinary waves that crash along the shore, and you probably have
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seen videos of giant tsunami waves that have traveled across open water.
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But there's another kind of wave that dwarfs them all, and it can stretch for thousands
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of miles.
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It's called a Kelvin wave.
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It's a massive, slow-moving pulse of warm water traveling eastward along the equator.
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Think of the Pacific Ocean like a giant bathtub.
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If you slosh the water, a wave will roll from one end to the tub to the other.
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An ocean Kelvin wave acts like that slush, but on a planetary scale.
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And here's the twist.
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If you were floating in a boat on top of one, you probably wouldn't even notice.
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The ocean surface may only rise by a few inches, but the real action is happening below.
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The tropical Pacific is layered.
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You have warm water near the surface, and much colder water below.
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In between, sits a boundary that's called the thermocline.
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Think of the thermocline like a ceiling of a cold basement.
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During a down-welling Kelvin wave, the warm, upper layer becomes thicker, and the thermocline
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is pushed deeper, sometimes by tens of meters.
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That extra thickness of warm water also raises the sea surface slightly.
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And because the warm water takes up a little more space than cold water, the effect becomes
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large enough for satellites to track it from space.
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Even stranger, the waves don't drift towards the poles.
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Because of the way the Earth spins, the equator acts almost like a set of invisible guardrails,
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helping to keep the wave concentrated near the equator as it travels eastward towards
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South America.
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It's not a crashing wall of water.
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It's more a broad, deep pulse of stored heat that travels thousands of miles across
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the Pacific over a matter of weeks to a few months.
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Once you picture that warm, pool-shifting east, the connection to El Nino becomes crystal
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clear, because something powerful had to start that water sloshing in the first place.
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So what was it?
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The answer?
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Wind.
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Under normal conditions, steady breezes call the trade winds blow across the tropical Pacific
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from the east to the west.
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Day after day, those winds push the surface water towards Indonesia and the western Pacific.
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Over time, the water literally piles up.
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In fact, the sea's surface and the western Pacific usually sits higher than it does thousands
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of miles away near South America.
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Sometimes as much as 15 to 20 inches higher.
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Think back to our bathtub.
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As long as your hand is pushing the water towards one end, that end stays higher and fuller.
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Now imagine your hand gets tired or you just stop pushing, or even better imagine giving
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the water a quick shove in the opposite direction.
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Now all that piled water has nowhere to go but backward.
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And that's exactly what happened in the Pacific earlier this year.
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During several periods in 2026, the usual east to west trade winds weakened.
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And in some cases, temporarily reversed.
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In parts of the western Pacific, air began blowing hard towards the east.
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Meteorologists call these Westerly Windbursts.
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They may only last for a week or two, but across an ocean holding trillions of gallons of
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sun-warmed water, that change provides a massive shove.
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And the shove triggered a Kelvin wave.
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Beginning earlier this year, satellites started spotting these pulses on the move.
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NASA's Sentinel-6 satellite detected a small Kelvin wave near Micronesia in late January.
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Then a much stronger pulse formed in March and began moving east.
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By the middle of May, it had traveled thousands of miles and reached the coast of South America.
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Near Peru, sea levels measured about 6 inches above average.
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Now remember we'll be covered in our first segment.
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A few extra inches at the surface means an enormous bulge of warm water beneath.
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And that matters because of how El Nino works.
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An El Nino develops when unusually warm water spreads across the central and eastern Pacific.
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And starts talking to the atmosphere above it.
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As Kelvin waves transport warm pools eastward, they build that exact setup.
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And here's the connection.
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Warm water adds heat and moisture to the air above it.
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That helps to shift where large areas of tropical thunderstorms develop.
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That changes the pattern of rising and sinking air on the cross the Pacific,
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which can weaken the trade winds even further.
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The ocean talks to the air.
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The air responds and changes the ocean.
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Scientists call this a feedback loop.
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Kelvin waves don't create the El Nino on their own.
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Instead they act like little delivery trucks, moving the warm water and the stored heat eastward
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into the part of the Pacific where El Nino develops.
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By September, NOAA reported water temperatures in the eastern Pacific
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running more than 3 degrees Celsius above normal with extreme heat reaching deep below the surface.
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That brings us to a major roadblock.
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That warm pulse has crossed the entire ocean, and South America is standing directly in its path.
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So what happens when that Kelvin wave finally hits South America?
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The Kelvin wave, the warm pulse that traveled thousands of miles across the equator,
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has reached places like Ecuador and Peru.
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A solid wall of rock and soil is blocking its path.
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When the wave reaches South America, it can't keep traveling east.
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Instead, part of the disturbance turns and begins moving along the coastline,
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both north and south from the equator.
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Scientists call this a coastily trapped Kelvin wave,
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and the name gives away the trick.
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Because of the way the Earth spins, the wave stays trapped close to the coastline
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as it travels north and south into the northern and southern hemisphere.
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Think of a train reaching the end of one line and switching onto a brand new track.
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The equator served as the tracks that guided the wave across the open Pacific.
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Now, the coastline of the Americas becomes a new set of tracks.
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And that means the impacts travel an astonishing distance.
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From the equator, the wave creeps past Central America, up the coast of Mexico,
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wraps around Baja, California, and heads straight for the beaches of the United States.
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The pulse scientists had been tracking was projected to follow that route.
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Forecast had it moving through the Gulf of California in late September,
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reaching San Diego in early October and then continuing north towards Los Angeles
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just a few days later.
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From there, it only takes a little more time to pass San Francisco
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before pushing into Oregon and Washington and all the way to Alaska.
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From its starting point in the western Pacific to its finish line in the Gulf of Alaska,
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the total trip spans 15,000 miles and takes about four months.
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If you stood on a California beach as it passed,
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you wouldn't see a towering crest or a Hollywood tidal wave.
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The ocean just sits slightly higher.
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Strong, coastily-trapped Kelvin waves can raise water levels, though, by 6 to 12 inches.
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Unlike a wind wave that this rolls past in seconds, that extra height lingers for weeks, even months.
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A few extra inches may not sound dangerous, but consider what happens when you stack other events on top of it.
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Add in a regular high tide.
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Add in a heavy surf from an offshore wind storm.
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Add in fierce coastal winds that push water inland.
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Suddenly, every single breaker gets a higher launching pad.
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Water claws, much farther up the sand.
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Waves begin smashing into sea walls, chewing away cliffs and flooding beach parking lots.
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And sea level is only half the story.
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Remember, this wave carries a blanket of warm water.
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As it moves north, it pushes down the cold, nutrient-rich water that normally rises to the surface along the coast,
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especially from San Francisco, northward.
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With fewer nutrients reaching the surface, phytoplankton growth can decline.
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And because these microscopic organisms sit near the base of the marine food web, those effects can ripple upward through fish, sea birds, and marine mammals.
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During the monster El Nino of 2015 to 2016, researchers tracked five or six of these waves riding up the Pacific Rim.
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With the current El Nino rapidly gaining strength, this wave may only be the opening act.
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Kelvin waves are nothing new.
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Neither is El Nino.
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Both systems were shuttling water back and forth across the Pacific long before humans started altering the atmosphere.
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It would be flat out wrong to say climate change created the Kelvin wave that's currently moving towards the west coast.
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The real story is what sets beneath it.
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The ocean carrying this wave has a higher baseline than it did a century ago.
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Global sea level has been rising for more than a century, and that rate of rise has accelerated in recent decades.
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Two basic science principles explain why.
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First, thermal expansion.
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When ocean water warms up, the molecules spread out, meaning warmer water physically takes up more room.
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Second, melting ice.
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Glaciers and polar ice sheets sitting on land are melting and dumping their fresh runoff into the sea.
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Together, these two forces are raising the ocean's starting line long before a seasonal storm or a Kelvin wave ever picks up.
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Picture walking up a staircase.
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Long term sea level rise moves the baseline of the ocean up one step.
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A passing Kelvin wave temporarily bumps that water another step.
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A ordinary high tide adds another.
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Chop and swell from a local storm can add yet another.
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Suddenly, water is spilling into roads, parking lots, and living rooms that have stayed dry for decades.
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Notice that none of those individual elements had to break any records on their own.
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The Kelvin wave does not need to be unprecedented.
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The tide doesn't have to be freakishly high.
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The storm doesn't have to be a hurricane.
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When you raise a launch pad, it takes far less extra push to cross thresholds and to damaging flooding.
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NOAA Oceanographer William Sweet calls us a double whammy.
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Decades of gradual sea level rise brought the ocean uncomfortably close to the edge of a town,
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and then El Nino arrives to temporarily add extra water right on top.
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NOAA projects that the tide gauges across the United States could log a medium of seven to twelve days of high tide flooding over the 2026-27 season.
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A new national record.
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Along the Pacific coast, NOAA expects El Nino to increase the number of flood days,
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and a Kelvin wave can temporarily push coastal water levels higher still.
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By 2050, NOAA projects a national average of between 55 and 85 high tide flood days each year.
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Flooding that used to demand an intense winter storm will happen on a quiet sunny Tuesday.
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Scientists are still researching whether a warming planet will alter the actual size or frequency of Kelvin waves themselves.
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That question is complicated and ongoing.
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But here's a critical takeaway.
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A Kelvin wave does not have to grow an inch stronger to cause far worse trouble on our shores.
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The extra water lifting our coastline right now is temporary.
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Eventually this wave will run its course and fade out.
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But the higher baseline beneath isn't going to disappear when the wave passes.
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And as global sea levels continue to rise, the next Kelvin wave may begin forming from an even higher starting point.
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Kelvin waves are strange.
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You can stand on a beach while one passes right by and never see a crashing crest or wall of water.
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Yet their few quiet inches can chew away coastlines, worsen neighborhood flooding, and disrupt entire marine ecosystems.
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Kelvin waves have always been part of our planet's rhythm.
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But what's changed is the ocean beneath them.
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And as sea levels climb, the invisible wave can produce consequences that are impossible to ignore.
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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, you've been too afraid to ask.
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Or if you have a differing opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at the climate translation at gmail.com.
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I'll see you next time.