El Niño-Southern Oscillation

The merger of two neutron stars is not just a collision. Even before they touch, they deform each other through tidal forces, and this deformation depends on how 'soft' or 'stiff' the matter inside is. Stiff matter resists more; soft matter changes shape more easily.

When two black holes merge, ripples spread across the fabric of spacetime — gravitational waves. But what if one of them isn't a run-of-the-mill black hole but something else — an exotic compact object?

Every year, as December approaches, the water off the coast of Peru becomes anomalously warm or anomalously cold. This is El Niño and La Niña, two phases of the same climate pendulum that swings in the equatorial Pacific. The pendulum is not a simple one: it remembers what happened to it several months earlier, and this memory determines which way it will swing next.

Two pendulums suspended from a single invisible spring swing in a shared air current. One always lags the other by exactly half a period: when the first swings left, the second is already returning from the right. By watching the first, you can tell where the second will be half a period later.

Every winter, the tropical Pacific Ocean seems to replay the same script: sea surface temperatures off the coast of Peru rise, trade winds weaken, and a wave of droughts and floods spreads across the planet. This is El Niño, and its peak almost always falls in December. Why winter in particular?

In the Pacific Ocean, there is a warm current that flows eastward against all the others. It is called the North Equatorial Countercurrent, or NECC. In normal years, this band of warm water, a few hundred kilometers wide, quietly carries heat from Indonesia toward the Americas.

An orchestra plays in a dark hall, and the listener hears only a hum: hundreds of instruments blend into a dense noise in which no melody can be discerned. That is roughly what spectra extracted from climate data by methods like the Koopman operator look like: hundreds of components, each with its own frequency, and it is unclear which ones are true musicians and which are the rattling of chairs.

The Sun doesn't burn steadily: it erupts in series. Like a campfire that dies down and then suddenly throws out showers of sparks, these "fiery seasons" last from six months to a year and a half, and during them the star shows an unusually high number of sunspots.

Enceladus is a tiny moon of Saturn, covered in a thick crust of ice. Beneath it sloshes a salty ocean, and deep down, a hot, porous core may be at work, like a sponge soaked with water and heat. But how do you see through tens of kilometers of ice? No need to drill: you can use an electromagnetic "echo." A person with a metal detector walks along a beach.

For 800,000 years, ice ages have occurred every 100,000 years. The rhythm matches the elongation of Earth's orbit. But the orbit changes the flow of solar heat so subtly — as if the conductor barely moved the baton, yet the orchestra thundered. It remained a mystery how this weak signal controls the ice sheets.

A barometer on Tahiti and one in Darwin, Australia, breathe in opposite phases. When pressure rises on one, it falls on the other, and this difference, known as the Southern Oscillation Index, serves as a pendulum for the global climate.

Beneath Enceladus's icy crust churns an ocean, acting like a perfect heat pump. It pushes heat from the equator to the poles, spending a thousand times less energy than it transports — like a perpetual motion machine built into the moon. The secret lies in salt.

In summer, the Arabian Sea breathes like a pair of bellows: one moment it pumps heat, the next it exhales moisture over a billion people. But sometimes this breathing stumbles, and the water off the coasts of India and Pakistan runs a few degrees hotter than usual.

Two pendulums hang on the same wall, swinging out of sync, but suddenly they move as one, only with an 18-month delay. One pendulum is the Indian monsoon, the seasonal wind that brings rain to South Asian farmland. The other is the deep water of the tropical oceans, which slowly accumulates heat and remembers it for years.

Every few years, the Pacific Ocean off Peru warms so abruptly that fish disappear and rains flood the desert. This phenomenon is called El Niño, and it acts like a pendulum that swings the planet's climate. But when the planet itself warms, the pendulum behaves strangely: first its swing widens, then it suddenly fades.

The bronze plates of a gamelan do not sound according to a single tuning standard: each orchestra on Java keeps its own tuning, and two neighboring ensembles may play the same melody in slightly different intervals.

Two barometers hang on the wall. One reads clear, the other says partly cloudy. Which weather do you trust? That is roughly the question facing a group of climate scientists when two independent methods predicted different futures for the Pacific Ocean in 2026.

A student learned physics from a textbook and is taking an exam. The first two problems are solved brilliantly, but on the third, they err on something not covered in the book. That is roughly what the hybrid atmospheric model NeuralGCM faced when run through three levels of testing: cyclones, El Niño, and anomalous warming.

The same explosion can sound different: it all depends on which way the wind is blowing. In 2024, researchers set off charges equivalent to ten tons of TNT twice and recorded the sound with a network of 31 microphones spread over a radius of 23 kilometers. The source was identical, but the acoustic pictures turned out to be quite different.

The Pacific Ocean breathes slowly and deeply. Every few years, its warm surface waters shift eastward toward the coast of South America, and then Peru gets drenched while Australia goes up in flames. A year or two later, the water retreats, and the picture flips. This breathing is called El Niño, and until now its rhythm could only be guessed a couple of steps ahead.

For a long time, the climate of ancient Mars remained a mystery: the beds of dried-up rivers spoke of water, but models couldn't explain how it got there — after all, 4 billion years ago the Sun shone 30% dimmer. New research shows that the planet swayed, as if on a swing, between long glaciations and short wet epochs.

The tropical Pacific Ocean heats and cools like a giant battery, and its rhythm affects weather from India to Canada. This rhythm is called El Niño–Southern Oscillation, or ENSO for short. Forecasting it months ahead is like predicting when a pot will boil without knowing the strength of the flame.

The Sun is slowly brightening, and in hundreds of millions of years its heat would become lethal for Earth. Fortunately, the built-in planetary thermostat — the carbon cycle — when overheating triggers rocks to absorb carbon dioxide faster, cooling the climate.

In 1997, the Pacific Ocean warmed so much that corals bleached from Indonesia to the Galápagos, and floods and droughts swept across five continents. Such events, which climate scientists call extreme El Niños, occur every few decades, and to understand how often they will arrive in the future, we need thousands of years of observations.

A warm ocean off the coast of Peru can make winter in Moscow unusually mild. Climate scientists call these invisible threads that link weather in distant corners of the planet teleconnections. For a long time, they were thought of as something like permanent wiring: the signal sources may pulse, but the wires themselves lie still.

The Pacific Ocean is like a giant swing: warm water piles up in the west, then slides toward the east, and the temperature off the coast of South America jumps. Such warm years are called El Niño, and cold ones La Niña. But the swing doesn't move on its own: it's pushed by the wind.

Every day, about 40,000 thunderstorms flash across the planet. In that moment, the atmosphere resembles an orchestra without sheet music: warm air rises like a bow stroke, winds aloft carry the melody, and lightning punctuates the finale. But who conducts this orchestra?

Two conductors stand before one orchestra. One waves the baton quickly, setting the tempo every few bars. The second is almost motionless, but his slow breathing changes the overall sound throughout the symphony. So it is in the tropical Pacific: one part of the wind governs the fast oscillations of El Niño, the other governs decadal climate shifts.

Imagine an interpreter in a negotiation room who hears the tropics whisper and repeats it too loudly. That is how the neural-network climate model DLESyM behaves when forced with real Pacific sea surface temperatures. The ocean whispers "El Niño," and the atmosphere shouts back as if being shaken by the shoulders.

A camera on a tripod shoots the same landscape for decades. If you don't touch the lens, the images get hazy: the landscape changes, but the focus stays put. That's roughly how climate norms work. According to World Meteorological Organization rules, they are calculated as the average over the last 30 years.

Every spring, El Niño forecasts lose their edge, like a translator who gets distracted by every rustle in the room and turns a one-hour meeting into a two-hour one. Scientists call this the spring predictability barrier: in March and April, models that confidently predicted a warm phase in the Pacific back in January start making mistakes twice as often.

Imagine a pendulum that is pushed in time with the seasons: harder in winter, softer in summer. But this pendulum has a quirk: a switch that operates with a delay. When the pendulum passes through zero, the switch clicks and changes the direction of the push. That is exactly how the simplified El Niño model built by mathematicians works.

A team of forty forecasters prepares an El Niño forecast two years ahead. Each works with the same model but slightly different initial conditions and settings, so their outputs diverge. Typically, forecasting centers average all forty opinions, assuming each member is equally useful.

In a room with 80 advisors, each shouts their own opinion, and if you simply listen to everyone and take the average, you get mush. So it is with El Niño forecasts: a model produces 80 possible futures, but not all are equally useful. Some err less often, others more, and still others talk about something else entirely.

In summer, the South China Sea can show a strange pattern: the water in the north warms while the south cools at the same time. A year later, it's the opposite. This isn't random; it's a steady seesaw that the ocean rocks every summer.

An invisible relay race runs through Earth's tropics: a wave of heavy rain and winds, which meteorologists call the Madden–Julian Oscillation, travels eastward at about five meters per second. Most runners tire quickly, but rare marathoners carry the torch all the way across the Pacific.

The tropical Pacific Ocean lives in two rhythms. The first is fast: a wave of thunderstorms born over the Indian Ocean races eastward and dies out off the coast of the Americas within a month or two. The second is slow: every few years, the ocean surface warms enough to alter weather across the entire planet. That is El Niño. Between these rhythms lies a bridge, and building it took climatologists decades.

You can sit on a seesaw and pump your legs, or you can just tip from one side to the other. The Pacific Ocean does both. Every few years, warm water off the coast of Peru gives way to cooler water, and rainfall patterns, winds, and entire ecosystems across half the planet reshuffle. These shifts are called El Niño and La Niña, together known as ENSO: Earth's climate seesaw.

Picture a pendulum hanging in a room with drafts. Sometimes a gust pushes it harder, sometimes softer. If the pendulum barely loses energy, it will swing long and steady. But if friction is strong, each push quickly fades, and the motion becomes jerky: a sharp swing, then a long sway. That's exactly how the tropical Pacific behaves when the heat of El Niño gives way to the cold of La Niña.

From July 2023 to July 2024, Earth's atmosphere gained carbon dioxide at a rate of 3.66 parts per million per year. That is the fastest pace since 1979. The reason is not that factories and cars suddenly started emitting more CO₂. The planet's lungs—forests and soils—took a shallower breath. The planet breathes through its green cover.