The Day Is Getting Longer: How Climate Change Is Slowing Earth's Spin at a Rate Unseen in 3.6 Million Years

The melting of Earth's polar ice sheets is not merely raising sea levels — it is fundamentally altering the planet's rotation, stretching each day by fractions of milliseconds in a phenomenon that new research shows is unprecedented in at least 3.6 million years. As water once locked in polar ice flows toward the equator, Earth's spin decelerates in a process physicists liken to a figure skater extending their arms. The consequences ripple from the abstract — the very definition of a second — to the concrete: GPS navigation, financial markets, and the global power grid.

The Discovery That Rewrites Planetary History

In March 2026, researchers Mostafa Kiani Shahvandi of the University of Vienna and Benedikt Soja of ETH Zurich published a landmark study in the Journal of Geophysical Research: Solid Earth that placed modern changes to Earth's rotation in deep geological context [1]. Their conclusion was stark: the current rate at which days are lengthening — 1.33 milliseconds per century — has no parallel in at least 3.6 million years, stretching back to the Late Pliocene epoch.

"This rapid increase in day length implies that the rate of modern climate change has been unprecedented at least since the late Pliocene," the researchers wrote. Soja added bluntly: "This rapid increase can be attributed primarily to human influences" [1].

The team achieved this sweeping historical comparison through an innovative methodology. They analyzed the fossilized remains of benthic foraminifera — single-celled marine organisms whose chemical composition records ancient ocean conditions — to reconstruct sea-level fluctuations over millions of years. From those sea-level records, they mathematically derived corresponding changes in day length using a physics-informed probabilistic diffusion model, a type of deep learning algorithm designed to handle the inherent uncertainties of paleoclimate data [1].

Their reconstruction revealed that only one period in the past 3.6 million years even comes close to the current rate: approximately 2 million years ago. And even that period falls short of what humanity is producing through greenhouse gas emissions today.

The Physics of a Slowing Planet

The mechanism behind this phenomenon is elegant in its simplicity. Earth's rotation speed is governed by the distribution of its mass relative to its spin axis — the same conservation of angular momentum that governs a figure skater's pirouette. When mass is concentrated near the axis (the poles), Earth spins faster. When mass shifts outward toward the equator, Earth slows.

Climate change is driving precisely this redistribution. As global temperatures rise, the Greenland and Antarctic ice sheets — massive concentrations of frozen water at Earth's poles — are losing mass at accelerating rates. NASA's GRACE and GRACE Follow-On satellite missions have tracked this loss with precision: Greenland has shed approximately 264 gigatons of ice per year between 2002 and 2025, while Antarctica has lost roughly 135 gigatons annually over the same period [3]. Combined, these losses raise global sea levels by approximately 1.2 millimeters per year.

That meltwater does not stay at the poles. It flows into the world's oceans, spreading predominantly toward the equator. Earth's waistline, in effect, expands. The planet becomes slightly more oblate — wider at the middle — and its rotation decelerates.

"It's a testament to the gravity of climate change, in a sense," said Surendra Adhikari of NASA's Jet Propulsion Laboratory, a co-author of a 2024 study in the Proceedings of the National Academy of Sciences that first quantified the acceleration of this effect [4].

An Accelerating Trend

The PNAS study, led by Shahvandi and Adhikari and published in July 2024, established that the climate-driven lengthening of days is not merely occurring — it is accelerating [4]. Their analysis showed that the climate-induced increase in day length varied between 0.3 and 1.0 milliseconds per century throughout the 20th century. Since 2000, however, that rate has jumped to 1.33 ± 0.03 milliseconds per century — faster than at any point in the prior hundred years.

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

Data as of Mar 13, 2026CSV

The projections grow more alarming. Under high-emission scenarios, the researchers found that the climate-induced rate of day lengthening could reach 2.62 milliseconds per century by the end of the 21st century [5]. At that rate, climate change would overtake the gravitational pull of the Moon as the dominant force affecting Earth's day length — a remarkable threshold given that lunar tidal friction has been the primary driver of day-length changes for billions of years.

Competing Forces Inside the Earth

The story of Earth's rotation is not solely about ice melt. Multiple forces act simultaneously on the planet's spin, sometimes in opposing directions.

The Moon's gravitational tides have been slowing Earth for eons, at a relatively steady rate of about 2.3 milliseconds per century. This is the reason why a day 400 million years ago lasted only about 22 hours.

Post-glacial rebound — the slow rising of Earth's crust in regions like Canada and Scandinavia, still recovering from the weight of ice age glaciers that melted roughly 10,000 years ago — actually speeds up Earth's rotation by concentrating mass closer to the spin axis [6].

And deep within the planet, changes in Earth's liquid outer core have been causing the solid mantle to speed up. Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography who published a foundational study on this topic in Nature in March 2024, found that core-mantle interactions have made a day approximately 0.0025 seconds shorter over the past 50 years [7].

"This is another one of those 'this has never happened before' things," Agnew said of the interplay. "The idea that this effect is large enough to change the rotation of the entire Earth" [8].

It is the tension between these forces — the core speeding Earth up, ice melt slowing it down — that creates a complex and unprecedented situation for global timekeeping.

The Leap Second Crisis

Since 1972, the world has added 27 leap seconds to Coordinated Universal Time (UTC) to keep atomic clocks synchronized with Earth's slightly irregular rotation [7]. These have always been positive — an extra second inserted, usually at the end of June or December.

But the speedup of Earth's crust, driven by core-mantle interactions, was pushing the planet toward an unprecedented moment: the need for a negative leap second, in which a second would be subtracted from UTC. Agnew's 2024 analysis in Nature projected this would have been necessary by approximately 2026 [7].

Climate change intervened. The accelerating polar ice melt has slowed Earth's rotation enough to delay the need for a negative leap second to approximately 2029, Agnew calculated [7]. Global warming, in this narrow sense, has bought the world's timekeepers a few years of breathing room.

This is not entirely welcome news. A negative leap second has never been implemented, and computer scientists and engineers have warned that the consequences could be severe. Systems designed to handle an added second may fail catastrophically when asked to subtract one. Financial transaction timestamps could become disordered. Telecommunications networks could experience sequencing failures. GPS coordinates could briefly lose accuracy [9].

"Technology may be [sensitive to timing adjustments], and people use technology without realizing the sensitivity," warned Judah Levine of the National Institute of Standards and Technology [5].

Recognizing the growing complexity of the problem, the General Conference on Weights and Measures voted in November 2022 to phase out leap seconds entirely by 2035, allowing astronomical time to drift further from atomic time before any correction is applied [7]. But the transition itself presents enormous logistical challenges for global infrastructure.

The Broader Planetary Transformation

The rotation changes are one manifestation of a broader transformation that climate change is imposing on Earth's fundamental geophysical properties. Research has shown that ice melt is not only slowing the planet's spin but also physically shifting the location of its rotational axis — a phenomenon known as polar motion [10]. The poles are, quite literally, wandering in response to the redistribution of water mass across the planet's surface.

Source: NASA PO.DAAC / Satellite Altimetry

Data as of Mar 13, 2026CSV

Meanwhile, the sea-level rise that drives these rotational changes continues to accelerate. Satellite altimetry data shows that the rate of global mean sea level rise has more than doubled in three decades, from approximately 2.1 mm per year in 1993 to approximately 4.5 mm per year in 2023 [11]. A 2024 study in Communications Earth & Environment confirmed this doubling trend using 30 years of satellite measurements [12].

Harvard geophysicist Jerry X. Mitrovica has placed these findings in perspective: "Despite our perceptions as humans, the Earth is not a perfect timekeeper" [8]. What is new is that humanity has become a force capable of altering that imperfect timekeeping in measurable, historically unprecedented ways.

What Milliseconds Mean for Modern Life

A millisecond per century sounds trivially small. It is not. Modern civilization has built systems of extraordinary temporal precision that depend on accurate knowledge of Earth's rotation.

GPS satellites, which enable everything from navigation to precision agriculture, derive positioning data from signals timed to billionths of a second. Financial markets execute trades in microseconds, with transaction timestamps that must maintain strict chronological order across global exchanges. Power grids synchronize electricity generation across continental distances using time signals traceable to UTC [5][9].

Even space exploration is affected. As Soja noted in the 2026 study, "precise space navigation requires accurate information on Earth's rotation" [1]. A spacecraft traveling at thousands of kilometers per hour accumulates meaningful positional error from even tiny inaccuracies in rotational data.

The practical upshot is that climate change is not only reshaping coastlines, weather patterns, and ecosystems. It is altering a property of the planet so fundamental that human civilization has historically treated it as a given: the length of a day.

The View From Deep Time

Perhaps the most sobering aspect of the 2026 Vienna-ETH study is its temporal scope. By reaching back 3.6 million years, the researchers placed human influence on Earth's rotation in the context of numerous natural climate cycles — glacial advances and retreats, volcanic eruptions, orbital variations. Through all of those upheavals, day length changed. But it never changed this fast.

The Late Pliocene, the starting point of their analysis, was the last time atmospheric CO2 concentrations were comparable to today's levels. Global temperatures were 2-3°C warmer than pre-industrial levels, and sea levels were 15-25 meters higher. It was a world profoundly different from the one in which human civilization arose.

That we are now changing the planet's rotation faster than anything in 3.6 million years is a measure of the scale and speed of the current transformation. The days are growing longer. The change is too small for any human to feel. But the planet registers it, and the instruments that modern civilization depends on register it, too. In milliseconds, the Earth is keeping its own account of what is happening to the climate.