Earth's Rotation Slowing at Unprecedented Rate in Millions of Years

The planet beneath our feet is spinning more slowly than at any point in the past 3.6 million years, and for the first time in Earth's long geological history, the primary cause is not the gravitational pull of the Moon—it is us.

A landmark study published in March 2026 in the Journal of Geophysical Research: Solid Earth has quantified the extent to which human-caused climate change is decelerating Earth's rotation [1]. Researchers Mostafa Kiani Shahvandi of the University of Vienna and Benedikt Soja of ETH Zurich found that since 2000, Earth's days have been lengthening by approximately 1.33 milliseconds per century—a pace that has no parallel in the geological record going back to the Late Pliocene epoch [2].

The implications stretch far beyond academic curiosity. From the global timekeeping infrastructure that underpins financial markets and power grids to the precision navigation systems guiding spacecraft, the steady deceleration of our planet's spin is already forcing a reckoning with how humanity measures time itself.

The Physics of a Slowing Planet

The mechanism behind Earth's rotational slowdown is elegant in its simplicity, even as its consequences are profound.

As global temperatures rise, vast ice sheets in Greenland and Antarctica—along with mountain glaciers worldwide—are shedding mass at accelerating rates. Between 2002 and 2025, Greenland alone lost approximately 264 gigatons of ice per year, contributing roughly 0.8 millimeters annually to global sea level rise [3]. That meltwater flows into the world's oceans, where it pools disproportionately at lower latitudes near the equator.

This redistribution of mass from the poles to the equator increases Earth's moment of inertia—the rotational equivalent of a figure skater extending her arms mid-spin. "It's similar to a figure skater who spins more slowly once they stretch their arms," Shahvandi explained in a University of Vienna press release [2]. The physics is inescapable: as mass moves farther from the axis of rotation, the planet must spin more slowly to conserve angular momentum.

Source: NASA PO.DAAC / Satellite Altimetry

Data as of Mar 14, 2026CSV

The rate of global sea level rise has itself accelerated dramatically. Satellite altimetry data shows the rate has more than doubled, from approximately 2.1 millimeters per year in 1993 to 4.5 millimeters per year by 2024 [4]. Each increment of sea level rise represents additional mass redistributed toward the equator, compounding the rotational drag.

Decoding 3.6 Million Years of Spin History

What makes the new research particularly striking is its temporal scope. Kiani Shahvandi and Soja did not simply examine modern satellite measurements—they reconstructed a continuous record of Earth's rotational changes stretching back 3.6 million years to the Late Pliocene [1].

Their method relied on fossilized benthic foraminifera—single-celled marine organisms whose shells, preserved in ocean sediments, serve as chemical archives of ancient sea levels. By analyzing the oxygen isotope ratios locked within these microscopic fossils, the researchers could trace historical sea-level fluctuations and, from those, derive corresponding changes in day length [2].

To manage the inherent uncertainties of paleoclimate data, the team developed what they call a "physics-informed diffusion model" (PIDM)—a computational framework that combines the physical laws governing Earth's rotation with statistical techniques to extract signals from noisy geological records [1].

The result was a continuous 3.6-million-year timeline of day-length variation. Throughout the entire Quaternary period—the past 2.6 million years of ice age cycles, when massive continental glaciers waxed and waned across North America, Europe, and Asia—nothing matched the current rate of change. Only around 2 million years ago did rates approach comparable levels, but even then, the researchers found they "never matched today's speed" [2].

The Ancient Braking System: Tides and the Moon

To appreciate why the current acceleration matters, it helps to understand the natural forces that have shaped Earth's rotation over geological time.

For billions of years, the dominant force slowing Earth's spin has been tidal friction—the gravitational interaction between Earth and the Moon. The Moon raises tidal bulges in Earth's oceans; because Earth rotates faster than the Moon orbits, these bulges are dragged slightly ahead of the Earth-Moon line. The resulting gravitational torque gradually transfers rotational energy from Earth to the Moon, slowing our planet's spin while pushing the Moon into an ever-wider orbit [5].

This tidal deceleration currently adds about 2.3 milliseconds to the length of day per century, and it has been doing so, with variations, for eons. The Moon retreats from Earth at a rate of 3.8 centimeters per year, as measured by lunar laser ranging experiments that bounce laser beams off retroreflectors left on the lunar surface by Apollo astronauts [5].

But the geological record shows this rate has not been constant. Over the past 620 million years, the average rate of lunar recession was only about 2.17 centimeters per year—roughly half the current rate [5]. Continental configurations, ocean basin shapes, and the resonant properties of tidal systems all modulate how efficiently tides dissipate energy.

What is new and alarming is that climate change is now adding a second, increasingly powerful braking force on top of tidal friction.

When Climate Overtakes the Moon

The 2024 PNAS study by Kiani Shahvandi, Soja, and collaborators including Surendra Adhikari of NASA's Jet Propulsion Laboratory and Mathieu Dumberry of the University of Alberta quantified a startling trajectory [6]. They found that the climate-driven component of day-length change has been accelerating throughout the 20th and 21st centuries, and that "the present rate of increase is higher than at any point in the 20th century" [6].

Under high-emission scenarios, the researchers projected that the climate-induced rate of day lengthening could reach 2.62 milliseconds per century by the end of the 21st century—more than double the current rate and exceeding the contribution from lunar tidal friction [6]. In other words, for the first time in Earth's 4.5-billion-year history, human activity could become a more powerful force shaping the planet's rotation than the Moon's gravity.

Source: PNAS / Kiani Shahvandi et al. (2024)

Data as of Mar 14, 2026CSV

The Competing Tug: Earth's Liquid Core

The story of Earth's rotation is not a simple tale of unidirectional slowing. Beneath the planet's rocky mantle, a turbulent ocean of liquid iron churns in complex convective patterns, generating Earth's magnetic field—and occasionally speeding up the planet's spin.

Over roughly the past 50 years, changes in the liquid outer core have been accelerating Earth's rotation, partially counteracting the combined effects of tidal friction and ice melt [7]. This core-driven speedup is what produced a curious phenomenon: in 2020, Earth experienced 28 of its shortest days since precise atomic clock measurements began in the 1960s [7]. On June 29, 2022, the planet completed a rotation 1.59 milliseconds faster than the standard 86,400 seconds [8].

This speedup raised the prospect of something never before attempted in the history of timekeeping: a negative leap second, in which a second would be subtracted from Coordinated Universal Time (UTC) rather than added [7]. Since 1972, 27 positive leap seconds have been inserted into UTC to keep atomic clocks aligned with Earth's gradually slowing rotation. A negative leap second would have been an unprecedented reversal.

But the ice melt effect has been working against the core speedup. Duncan Agnew of the Scripps Institution of Oceanography estimated in a 2024 study that ice melt has delayed the need for a negative leap second from approximately 2026 to 2028 or 2029 [7]. As Agnew noted, "this effect is large enough to change the rotation of the entire Earth" [7].

The 30-Foot Wobble

Earth's rotation is not just slowing—its axis is physically shifting. NASA-funded research has shown that the planet's spin axis has meandered approximately 30 feet (10 meters) over the past 120 years, and scientists have attributed nearly all of the periodic oscillations in its position to climate-related changes [9].

A study led by Adhikari at JPL found that around the year 2000, Earth's rotational axis underwent a sudden eastward drift, which the researchers linked to the accelerating melt of the Greenland and Antarctic ice sheets and the depletion of groundwater reserves in Eurasia [9]. Using more than 120 years of observational data, the team determined that 90% of recurring fluctuations in the axis position between 1900 and 2018 could be explained by changes in groundwater, ice sheets, glaciers, and sea level [9].

This polar motion—the technical term for the wandering of Earth's rotational axis—has practical consequences. Navigation systems, satellite positioning, and astronomical observations all depend on precisely knowing where Earth's axis points. As climate change accelerates the redistribution of mass across the planet's surface, these corrections become increasingly significant.

Implications for Timekeeping and Technology

The millisecond-scale changes in day length may sound trivial, but they ripple through the technological systems that undergird modern civilization.

Coordinated Universal Time, the global time standard, has relied on leap seconds since 1972 to reconcile the drift between ultra-precise atomic clocks and the irregular rotation of Earth. In 2022, the General Conference on Weights and Measures voted to abolish leap seconds by 2035, in part because they create headaches for computer systems, financial trading platforms, and telecommunications networks [7].

The prospect of a negative leap second—a phenomenon that has never occurred—alerted technologists to a potentially more disruptive scenario. Software systems designed to handle the occasional addition of a second have never been tested for the subtraction of one. Jerry X. Mitrovica, a Harvard geophysicist, observed that "the Earth is not a perfect timekeeper," underscoring the challenge of building precision infrastructure atop a platform whose rotation speed is subject to competing geological and climatological forces [7].

Space navigation presents perhaps the most acute challenge. Missions to Mars and beyond require exquisitely precise knowledge of Earth's rotational state to calculate trajectory corrections. As Soja noted, the findings have direct implications for "precise space navigation, which requires accurate information on Earth's rotation" [2].

The Bigger Picture

The discovery that climate change is now a dominant force in Earth's rotational dynamics adds another dimension to an already extensive catalogue of planetary-scale consequences from greenhouse gas emissions. It joins sea level rise, ocean acidification, ecosystem disruption, and extreme weather intensification as evidence that human activity is altering the fundamental physical characteristics of the planet.

Source: NOAA Arctic Report Card / NASA GRACE

Data as of Mar 14, 2026CSV

The research also serves as a powerful illustration of the interconnectedness of Earth's systems. Ice that forms over millennia at the poles melts into water that flows toward the equator, subtly but measurably altering how fast a 6-sextillion-ton planet spins on its axis. The signal is detected by atomic clocks accurate to billionths of a second, confirmed by lasers bounced off mirrors on the Moon, and contextualized by the chemistry of microscopic organisms that died millions of years ago on the ocean floor.

As Kiani Shahvandi and Soja's work makes clear, the current trajectory is without precedent in at least 3.6 million years. And unlike the natural ice age cycles that drove past fluctuations in day length, the current trend is accelerating on a timescale of decades, not millennia. The question is no longer whether human activity is reshaping the planet's most basic physical properties—it is how far those changes will ultimately go.