Earth Rotation Slowing Dramatically

New research suggests that Earth’s rotation has been dramatically slowing.

Geophysics researchers in Vienna and Zurich are analyzing the variations in global sea levels from as far back as the Late Pliocene to estimate the changing rate of the Earth’s spin.

Study Findings

They discovered that between 2000 and 2020, the days have lengthened by 1.33 milliseconds per century – the most rapid rate at which the rotation of the Earth has slowed since mastodons and saber-toothed cats walked the planet.

“This rapid increase in day length implies that the rate of modern climate change has been unprecedented at least since the late Liocene, 3.6 million years ago,” wrote study co-author Benedikt Soja, a professor of space geodesy at ETH Zurich in a press statement, adding, “The current rapid rise in day length can thus be attributed primarily to human influences.”

Ocean-Induced Drag

Soja and his colleagues call this phenomenon “continental-coean mass redistribution” in their research, including their latest paper published Tuesday in the Journal of Geophysical Research: Solid Earth. As the glaciers and polar ice sheets melt into the oceans, extra water weight builds up in the lower latitudes near the equator, where all the extra mass is more likely to drag on Earth’s spin.

Soja’s co-author, Mostafa Kiani Shahvandi, compared the phenomena to “a figure skater who spins more slowly once they stretch their arms, and more rapidly once they keep their hands close to their body.”

“Only on time — around 2 million years ago — the rate of change in the length of day was nearly comparable, but never before or after that has the planetary ‘figure skater’ raised her arms and sea levels so quickly as in 2000 to 2020,” says Kiani Shahvandi, a postdoctoral researcher with the University of Vienna’s Department of Meteorology and Geophysics.

Sea-level fluctuation data were retrieved from the fossils of tiny, shelled, single-celled marine organisms called benthic foraminifera.

Shahvandi says, “From the chemical composition of the foraminifera fossils we can infer sea-level fluctuations and then mathematically derive the corresponding changes in day length.”

These researchers developed a new deep-learning method based on a Physics-Informed Diffusion Model (PIDM) for these calculations. “PIDMs take the powerful, predictive power of a probability-based, machine-learning AI and guide it within the strict constraints of physics-informed neural networks (PINNs), built on scientifically derived natural laws.

Shahvandi notes, “This model captures the physics of sea-level change, while remaining robust to the large uncertainties inherent in paleoclimate data.”

Why Thousandths of a Second Matter

The lengths of the days on Earth have been proven to vary minutely with recent times, where the rotation has sped up. On July 4, 2024, Earth clocked a personal planetary record, completing a full spin 1.66 ms faster than usual. Everything from the molten core of the planet to atmospheric pressure and wind to the shifting orbit of the Moon impacts the daily rotation of the Earth.

This new research focuses on long-term trends. The behaviors of Earth across decades of the 21st century, as compared to its rotational rate trends over millions of years.

Today’s increasing oceanic weight at the equator will increasingly become a dominant factor influencing the rotation speed of Earth.

“By the end of the 21st century, climate change is expected to affect day length even more strongly than the moon. Even though the changes are only milliseconds, they can cause problems in many areas, for example, in precise space navigation, which requires accurate information on Earth’s rotation,” says Soja.

Sources:

Gizmodo: Earth’s Spin Is Slowing at a Pace Not Seen in Millions of Years – and You Can Guess…
Scientific American: Earth’s days are getting longer at an unprecedented rate. Climate change to blame
La Bruiula Verde: Polar ice melt is slowing Earth’s rotation and lengthening days at an unprecedented rate in the last 3.6 million years

Featured Image Courtesy of Kevin Gill’s Flickr Page – Creative Commons License