The year Earth’s spin changed after massive La Niña event

For more than a century, Earth’s rotation pole has traced a circular motion roughly 10 m (33 feet) wide around the geographic North Pole every 433 days (1.19 years). This gentle oscillation, known as the Chandler Wobble, has remained stable since its discovery in the late 19^th century.

After 2015, that stability broke. Measurements from the International Earth Rotation and Reference Service showed that the amplitude of the Chandler Wobble collapsed to less than half its usual size. By 2017, only the annual wobble remained visible in polar motion records.

The collapse was unprecedented in the modern satellite era. The only comparable reduction happened between 1925 and 1940, when the wobble’s amplitude dropped and its phase shifted abruptly. Scientists had long debated whether random variations or external forces triggered that earlier event.

This time, researchers could track every change precisely. The 2025 study by Taehwan Jeon and colleagues used four decades of rotation data to find the fingerprints of the process that silenced Earth’s free wobble. Their results point to one remarkable conclusion: the cause lay several years earlier, hidden in the global climate system.

How a climate event set the stage

The story begins in 2010, when a strong La Niña reshaped the planet’s water cycle. The event shifted rainfall patterns across continents, increased flooding in Australia and South America, and reduced ocean mass as more water accumulated on land.

By 2011 and 2012, satellite observations showed large anomalies in atmospheric pressure and terrestrial water storage. These changes redistributed mass between hemispheres, subtly altering Earth’s inertia and the position of its spin axis.

Jeon’s team analyzed these mass changes using wavelet transform methods that reveal how signals vary across time and frequency. Their analysis showed that 2011–2012 contained the strongest excitation at the Chandler frequency, about 0.84 cycles per year, matching the timing that later led to the amplitude collapse.

When the researchers excluded this two-year window from their models, the post-2015 decline vanished. Earlier anomalies in 2002 and 2005 also influenced the wobble, but the 2011–2012 changes were the dominant trigger. The timing links directly to the hydrological impacts of the 2010–2011 La Niña.

In essence, a brief global redistribution of air and water during 2011 shifted the energy balance of Earth’s rotation. Four years later, the effect reached its peak when the free and forced wobble components canceled each other.

When two oscillations cancel each other out

Earth’s rotation pole moves because of two interacting motions. The free wobble is the planet’s natural oscillation, while the forced wobble comes from external excitations such as winds, ocean currents, and shifting water or air masses.

Normally, these two components stay in step, sustaining the wobble’s amplitude of about 10 m (33 feet). Around 2012, however, their phases drifted apart. When the forced wobble turned opposite in phase to the free motion, they began to cancel.

By 2015, the two motions were nearly 180 degrees out of phase. Their combination produced a smaller resultant amplitude that persisted for several years. Between 2017 and 2021, Earth’s rotation pole moved only a few meters instead of ten.

The study’s calculations tested a range of internal damping values, called the Chandler quality factor, from 40 to 180, and periods between 430 and 434 days. In every case, the phase cancellation held. The wobble collapsed not because of an internal change but because the external forcing had flipped in sign.

This behavior is similar to a pendulum being nudged at the wrong moment. Instead of amplifying the motion, each impulse lands when the pendulum swings back, gradually bringing it to rest.

Tracing the signals across Earth’s systems

To understand the physical drivers, the researchers compared multiple datasets. They used the IERS Earth Orientation Parameters from 1980 to 2024 and combined them with modeled excitations from the GeoForschungsZentrum (GFZ) in Potsdam.

The GFZ dataset separates excitation sources into atmospheric, oceanic, and hydrological components, each representing angular momentum changes that affect rotation. Satellite Laser Ranging data provided an independent check, tracking Earth’s gravity field through the low-degree coefficients known as C21 and S21.

All datasets showed the same pattern. Strong intra-annual variability appeared in 2011 and 2012, concentrated near the Chandler frequency. The hydrological term, which reflects continental water storage, produced the largest contribution.

When the excitation terms were used to reconstruct the wobble, the simulated amplitude dropped sharply after 2015, closely matching the observed pattern. Removing the 2011–2012 signals from the models prevented the collapse from occurring, confirming their main role.

The findings demonstrate that no single region controls Earth’s rotation. Instead, small, synchronized mass shifts across continents and the atmosphere combine to generate global-scale rotational effects.

Why tiny mass changes alter a planet’s spin

At first glance, the mass changes involved seem negligible. A redistribution of a few millimeters of water equivalent across continents might appear too small to matter. Yet, near resonance, even minute shifts have amplified effects.

The Chandler frequency acts as a natural amplifier. When excitations occur near this frequency, their influence on the rotation pole grows by an order of magnitude. This sensitivity explains why errors in atmospheric or hydrological models can lead to large discrepancies in predicted polar motion.

The post-2015 event shows that Earth’s rotational dynamics depend on the same climate forces that shape rainfall, drought, and ocean circulation. The planet’s spin integrates these processes into a single, global signal.

This sensitivity has practical consequences. Navigation satellites, astronomical reference frames, and geophysical monitoring systems rely on accurate Earth orientation data. Sudden changes in the Chandler Wobble can affect how these systems track position and time.

The event reminds us that Earth’s stability is relative. The same water that fills reservoirs and rivers also has the power to shift the axis of rotation by centimeters.

A window into Earth’s climate-rotation link

The 2025 study builds on decades of research that connect Earth’s hydrology to its rotation. Previous analyses showed that random fluctuations could sustain or damp the wobble, but they lacked the detailed global data now available.

Recent work has demonstrated that polar motion reflects the redistribution of mass from ice melt, groundwater depletion, and large-scale precipitation anomalies. Jeon’s results extend that concept by showing how one specific event can trigger a prolonged dynamical response.

The authors note that current geophysical models still fall short of fully reproducing observed amplitudes. Small uncertainties in groundwater flow or atmospheric pressure translate into large differences in rotation response. Improving these models will require continued satellite gravimetry and long-term monitoring of surface water and atmosphere.

If the Chandler Wobble remains in a low-amplitude phase for years, it could provide a natural experiment for studying the planet’s damping and excitation processes. Similar to the 1925–1940 episode, Earth may gradually regain its free wobble as excitation sources realign.

Understanding this interplay offers new insight into how the planet stores and releases angular momentum. The rotation of Earth is, in effect, a mirror of its changing climate.

Why this matters beyond geodesy

The collapse of the Chandler Wobble shows how tightly linked Earth’s systems are. A climate event lasting months produced a rotational change lasting years.

This coupling matters for more than curiosity. Polar motion records inform satellite orbit calculations, sea-level estimates, and the accuracy of global navigation systems. Changes in rotation also affect how astronomers align telescopes with celestial coordinates.

For climate scientists, the finding is a clear example of feedback between the atmosphere, hydrosphere, and solid Earth. Water that shifts across continents alters not only the shape of the planet but its orientation in space.

Maintaining this observational capability requires consistent data from missions like GRACE-FO, Satellite Laser Ranging, and Very Long Baseline Interferometry. Together, these systems form the backbone for monitoring the heartbeat of the Earth’s rotation.

Jeon and colleagues show that even the planet’s spin carries a record of climate variability. The Chandler Wobble acts as Earth’s rotational memory, quietly encoding the story of shifting air and water through time.

References:

¹ Diminished Chandler Wobble After 2015: Link to Mass Anomalies in 2011 – Taehwan Jeon et al. – Geophysical Research Letters – September 21, 2025 – https://doi.org/10.1029/2025GL116191 – OPEN ACCESS

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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