Humanity Is Slowing the Spin of the Earth — At a Rate Not Seen in 3.6 Million Years

A new study finds that melting ice sheets are dragging on the planet's rotation at a pace unmatched since before the dawn of the human species — and the effect is only accelerating.

For billions of years, only one force has meaningfully governed how fast the Earth spins: the Moon. Its gravitational pull on the oceans creates tidal friction that has been gradually slowing the planet's rotation since the first seas formed, stretching the length of a day by roughly 2.4 milliseconds per century [1]. It is a process so slow, so ancient, and so fundamental that it has shaped the very definition of time itself.

Now, a second force is making itself felt — and it is entirely of our own making.

A study published this week in the Journal of Geophysical Research: Solid Earth by researchers at the University of Vienna and ETH Zurich has found that human-caused climate change is lengthening Earth's days at a rate of 1.33 milliseconds per century, a pace unprecedented in the past 3.6 million years [2][3]. And if greenhouse gas emissions continue on their current trajectory, by the end of this century climate change will affect day length even more powerfully than the Moon — a gravitational partner that has been tugging at the Earth for 4.5 billion years [4].

The finding marks the latest in a series of discoveries revealing that humanity has become a geological force capable of reshaping the most fundamental properties of the planet: its axis, its rotation, and even how we keep time.

The Physics of a Slowing Planet

The mechanism behind the phenomenon is deceptively simple, rooted in a principle any figure skater understands intuitively.

When polar ice sheets and mountain glaciers melt, the water that was once concentrated at high latitudes flows into the world's oceans, pooling disproportionately around the equator. This redistributes the planet's mass outward from the axis of rotation, increasing what physicists call the moment of inertia. Because angular momentum must be conserved — a fundamental law of physics — the planet compensates by spinning more slowly [5][6].

It is the planetary equivalent of a skater extending their arms mid-spin. The mass moves farther from the center, and the rotation rate drops.

The numbers, at first glance, seem trivially small. A millisecond here, a fraction of a millisecond there. But the implications are anything but trivial.

3.6 Million Years of Context

What makes the new study exceptional is the deep-time perspective it brings to the question. Lead author Mostafa Kiani Shahvandi, a postdoctoral researcher at the University of Vienna's Department of Meteorology and Geophysics, and senior author Benedikt Soja, a professor of space geodesy at ETH Zurich, did not simply measure the current rate of change. They reconstructed how day length has varied over the past 3.6 million years — spanning the entire Quaternary period and reaching back into the late Pliocene [2][3].

Their method was ingenious. The team analyzed the fossil remains of benthic foraminifera, single-celled marine organisms whose chemical composition serves as a proxy for ancient sea levels. By inferring how ocean volume changed over millions of years, they could mathematically derive the corresponding shifts in Earth's rotation [3].

To manage the enormous uncertainties inherent in paleoclimate data stretching back millions of years, Shahvandi and Soja deployed a cutting-edge tool: a physics-informed diffusion model, a type of probabilistic deep learning algorithm constrained by the known physics of sea-level change [2][4].

The result was a 3.6-million-year record of day-length fluctuations — and within it, a stark conclusion. During the Quaternary period (roughly the last 2.6 million years), the repeated growth and melting of continental ice sheets during ice ages caused significant day-length variations. But nothing in that record matches what is happening now.

"The current rapid rise in day length can thus be attributed primarily to human influences," Soja stated in the University of Vienna's press release [3]. The last time day length changed at a comparable rate was roughly 2 million years ago — well before Homo sapiens first walked the Earth [2].

Source: Kiani Shahvandi & Soja (2026), Journal of Geophysical Research

Data as of Mar 14, 2026CSV

A Force to Rival the Moon

Perhaps the most striking projection in the study is what comes next.

The Moon's tidal drag — the ancient, patient force that has been slowing Earth's spin since the oceans formed — lengthens the day by approximately 2.4 milliseconds per century [1][7]. That has been the dominant rotational force for as long as the planet has had liquid water.

The current climate-driven rate of 1.33 milliseconds per century already represents more than half the lunar effect [2]. But under continued high-emissions scenarios, the researchers project the climate contribution could reach as high as 2.62 milliseconds per century by the end of this century — surpassing the Moon's influence entirely [4][7].

The idea that a single species, in barely two centuries of industrial activity, could generate a rotational effect comparable to the gravitational pull of a celestial body 238,900 miles away is, by any measure, extraordinary.

Where All That Ice Is Going

The underlying driver — accelerating ice loss — is well documented by satellite observations. Between 2002 and 2025, Greenland shed approximately 264 gigatons of ice per year, while Antarctica lost roughly 135 gigatons annually, according to NASA's GRACE and GRACE Follow-On satellite missions [8]. Their combined meltwater is enough to raise global sea levels by nearly 1.2 millimeters each year.

That rate, too, has been accelerating. Data from NASA and NOAA show that the rate of global sea-level rise has doubled over the past three decades — from about 2.1 millimeters per year in 1993 to approximately 4.5 millimeters per year by 2024 [9]. The total sea-level rise measured by satellites from 1993 to 2023 is 11.1 centimeters [9].

Source: NASA Sea Level Change Portal / NOAA

Data as of Mar 14, 2026CSV

Every millimeter of that rise represents mass that has migrated from the poles toward the equator, pulling on Earth's spin like an invisible brake.

Beyond Rotation: Axis Shift and Core Effects

The rotational slowdown is not the only way climate change is literally reshaping how the planet moves.

Research led by Surendra Adhikari at NASA's Jet Propulsion Laboratory has shown that the redistribution of mass from melting ice and depleted groundwater has shifted Earth's spin axis — the imaginary line around which the planet rotates — by roughly 30 feet (10 meters) from where it was in 1900, in the direction of Canada's Baffin Bay [10][11].

Around the year 2000, that drift suddenly changed direction, swinging eastward. Adhikari's team attributed the shift to the accelerating melt of the Greenland and Antarctic ice sheets, combined with groundwater depletion in Eurasia [10].

"In barely 100 years, human beings have altered the climate system to such a degree that we're seeing the impact on the very way the planet spins," Adhikari said [10].

Even deeper effects may be at play. A 2024 NBC News report highlighted research suggesting that surface mass changes are creating feedback effects that reach into the Earth's molten outer core, potentially influencing the fluid dynamics that generate the planet's magnetic field [11].

The Timekeeping Problem

The consequences extend from the abstract to the urgently practical.

Since 1972, the international timekeeping system has relied on "leap seconds" — one-second adjustments added to Coordinated Universal Time (UTC) to keep atomic clocks synchronized with the slightly irregular rotation of the Earth. Twenty-seven such leap seconds have been added since 1958 [7][12].

In recent years, however, the Earth's core dynamics had actually been speeding rotation slightly, raising the prospect that timekeepers might need to subtract a second for the first time — a "negative leap second." Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography, calculated that this unprecedented adjustment would have been needed around 2026 [12][13].

But climate-driven ice melt has delayed that scenario by approximately three years, pushing any potential negative leap second to around 2029. The melting ice's braking effect is counteracting the core-driven speedup [7][12].

"This is another one of those 'this has never happened before' things that global warming is responsible for," Agnew told Scientific American [13]. A negative leap second "would be a bigger problem because they've never had to do it."

The stakes may sound esoteric, but they are real. Telecommunications networks, financial trading systems, satellite navigation, and deep-space missions all depend on precise timekeeping synchronized to Earth's rotation. Even millisecond-level discrepancies can cascade into errors in GPS positioning, high-frequency trading, and spacecraft trajectory calculations [3][4].

The broader question of leap seconds may become moot: in 2022, the General Conference on Weights and Measures voted to abolish them by 2035, with a final review expected later this year [12][13].

The Bigger Picture

The rotational findings arrive against a backdrop of escalating climate impacts across every domain. Global energy consumption continues to climb — reaching 1,851 kilograms of oil equivalent per capita in 2021, up from 1,591 in 2000 [14]. The fundamental physics are clear: the more fossil fuels are burned, the faster ice melts, and the more the planet's rotation is altered.

Source: World Bank - World Development Indicators

Data as of Mar 14, 2026CSV

The study also underscores a methodological frontier. The combination of deep-time paleoclimate records, satellite geodesy, and physics-informed machine learning represents a new toolkit for understanding planetary dynamics. The researchers were able to peer 3.6 million years into the past and compare it with satellite-era precision — a synthesis that would have been impossible even a decade ago.

What It Means

Debates about climate change often center on temperature targets, sea-level projections, and extreme weather. The rotation findings add a dimension that is harder to wave away: humanity is altering the planet's fundamental mechanical properties.

The changes are small in absolute terms — no one will notice an extra millisecond in their morning. But they are measurable, accelerating, and, as of this week, confirmed to be without precedent in the geological record of the last 3.6 million years.

The Moon has been slowing the Earth since before life crawled onto land. The fact that a few centuries of fossil fuel combustion can generate a comparable effect is not just a scientific curiosity. It is a measure of the scale at which industrial civilization operates — and a reminder that the planet keeps its own accounts, down to the millisecond.