Days Are Getting Slightly Longer As Earth's Spin Is Slowing At An "Unprecedented Rate"

New research has confirmed that human-driven climate change is slowing Earth's rotation at a rate that is unprecedented for at least the past 3.6 million years. According to Phys.org, this phenomenon, often described using the "figure skater effect," occurs as melting polar ice caps and glaciers redistribute water toward the equator. This shift in mass increases the planet's moment of inertia, causing it to spin more slowly. Between 2000 and 2020, Earth's day length increased by 1.33 milliseconds per century due to climate-related mass redistribution.

"In our earlier work, we showed that the accelerated melting of polar ice sheets and mountain glaciers in the 21st century is raising sea levels, which slows Earth's rotation and therefore lengthens the day—similar 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," explained Mostafa Kiani Shahvandi of the University of Vienna's Department of Meteorology and Geophysics.

"What remained unclear was whether there were earlier periods when climate increased day length at a similarly rapid pace," Shahvandi added. 

Researchers from the University of Vienna and ETH Zurich used fossilised remains of tiny marine organisms called benthic foraminifera to unravel ancient day-length patterns. The chemical composition of the foraminifera fossils can infer sea-level fluctuations, helping scientists derive the corresponding changes in day length.

While the Moon's gravitational pull has historically been the primary driver of Earth's slowing spin (at ~2.4 ms/century), scientists predict that climate change could become the dominant influence by the end of the 21st century. Although a few milliseconds are imperceptible to humans, they are critical for systems requiring high-precision timekeeping, such as GPS satellites, space navigation, and complex financial networks. 

"This rapid increase in day length implies that the rate of modern climate change has been unprecedented at least since the late Pliocene, 3.6 million years ago. The current rapid rise in day length can thus be attributed primarily to human influences," says Benedikt Soja, professor of space geodesy at ETH Zurich.

"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," the professor added. 

Global Timekeeping Consequences

This slowdown is already impacting how we measure time. The increased day length has effectively delayed the need for a "negative leap second" from 2026 to at least 2029, giving timekeepers more room to adjust international guidelines. 

Accurate time measurement is crucial for computing systems, including GPS and space navigation, which rely on atomic clocks based on the frequency of specific atoms. Notably, these changes are unlikely to have a significant impact on human biology too, such as sleep patterns and circadian rhythms.

However, if global warming continues due to heat-trapping emissions, climate change is predicted to increase the length of a day by 2.62 milliseconds by the end of the century, according to scientific projections.