Melting ice makes the Earth spin harder, causing longer days

For ages, human actions have had little effect on Earth’s motions, i.e. its rotation rate and axis.

These motions were primarily driven by the Moon’s gravitational pull and internal processes in the core and mantle.

But now these natural movements are being challenged by melting ice sheets caused by human activity.

A new study reveals that Earth’s spin axis is “shifting” due to climate change and the planet’s internal dynamics.

Researchers at ETH Zurich used cutting-edge artificial intelligence models to better understand polar motion, which is the movement of the Earth’s rotation axis relative to the crust.

The study predicts that if greenhouse gas emissions continue to rise, the long-term influence of the moon’s tidal force will eventually prevail. For billions of years, the moon has determined the constant lengthening of our days.

“We humans have a greater influence on our planet than we realize. And this naturally puts a great responsibility on us for the future of our planet,” said Benedikt Soja, Professor of Space Geodesy at the Department of Civil, Environmental and Geomatics Engineering at ETH Zurich.

Extending days

Two recent studies have explored the surprising link between melting ice caps, the wobble of the planet and the length of our days.

Melting ice at the poles redistributes mass towards the equator and slows the Earth’s rotation. Water travels from the poles to the equator, disrupting the Earth’s balance.

As the ice melts on Earth’s surface, it slows the planet’s rotation and lengthens the day. Research from ETH Zurich shows that the slowdown slightly lengthens our days – just a few milliseconds compared to the typical 86,400 seconds.

There is a law in physics called conservation of angular momentum. It basically says that a rotating object likes to spin at the same speed unless something forces it to change. The rotation of the Earth also follows this rule. Melting ice redistributes matter, and this shift slows the Earth’s rotation according to law.

“This means that there is a displacement of mass and this affects the rotation of the Earth,” explained Soja.

Impact on the Earth’s core

Scientists have also studied why and how the Earth’s axis moves gradually over long periods of time. The team used physics-informed neural networks to create the most comprehensive model to date that explains how movements in the Earth’s core, mantle and surface climate contribute to polar movement.

These two studies highlight the complex web of interactions within the Earth. Events at the surface, such as ice melting, can have consequences deep within the core, and vice versa.

“Climate change causes the Earth’s rotation axis to move, and the feedback from the conservation of angular momentum also appears to change the dynamics of the Earth’s core,” explained Soja.

As the polar ice melts, the resulting water moves away from the poles toward the equator, causing the Earth to spin more slowly as it becomes bulkier. Benedikt Soja explained that this phenomenon is similar to a figure skater who spins more slowly when the arms are outstretched than when they are tucked in. The same principle applies to the rotation of the Earth.

“Therefore, ongoing climate change could even be affecting processes deep inside the Earth and be more far-reaching than previously thought,” Kiani Shahvandi, the study’s lead author and PhD student, added in a press release.