Human-driven climate change is slowing Earth’s rotation at a rate not seen in 3.6 million years, with sea level rise increasing the length of days by 1.33 milliseconds per century, according to a new study.
Earth spin faster when mass is more concentrated, just as spinning figure skaters pull their arms to increase speed and spread their arms out to slow down. Rising sea levels have long been known to redistribute that mass and change the planet’s spin, but the newly identified rate is unprecedented, scientists say.
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However, this speed of 2.4 milliseconds is offset by an effect called isostatic isostatic adjustment, which is the slow rise of the planet’s crust that continues to occur after the ice sheets have retreated. Glacial isostatic adjustment shortens day length by about 0.8 milliseconds per century, leading to a background elongation over time of 1.71 milliseconds per century (with about 0.1 millisecond uncertainty in the observations).
Other, short-term phenomena also affect day length, including strengthened winds during El Niño events, which slow the planet’s rotation by about a millisecond per century, Mann said.
In recent years, however, climate appears to be playing an increasing role in changing Earth’s rotation, study co-authors said Mostafa Kiani Shahvandia geoscientist at ETH Zurich. “I wanted to know if this was unusual or something like this happened in the past,” Shahvandi told Live Science. “As it turned out, it is quite anomalous. The effect is therefore anthropogenic (caused by humans).”
Shahvandi and study co-author Benedikt Sojaa professor of space geodesy at ETH Zurich, turned to the fossils of shelled single-celled organisms called foraminifera to look back millions of years into Earth’s day length. Changes in the oxygen content of these fossils could reveal sea levels when the organisms were alive, from which the researchers could extrapolate day lengths.
They found that today’s 1.33 milliseconds per century increase in day length was among the fastest changes seen in the past 3.6 billion years. “This is expected to be even bigger and even bigger than the effect of the moon,” Shahvandi said.
An episode around 2 million years ago saw a corresponding increase in day length of 2.1 milliseconds per century, the researchers found. It was in the early Pleistocene, a period when carbon dioxide in the atmosphere and temperature rose. There is some uncertainty in the historical estimate, which means that this period may have had a corresponding increase in day length as today, or that the day today may be faster.
Under a future warming scenario where greenhouse gases increase, the day could lengthen by 2.62 milliseconds per century by 2080, Shahvandi and Soja reported in their study, which was published March 10 in the journal JGR Solid Earth.
Although the impact is unlikely to be noticeable to humans, the findings have other real-world implications. For example, Mann said, instruments that require accurate knowledge of Earth’s rotation rate, such as those on spacecraft, may need to be recalibrated. Other precise timekeeping applications, such as in computing, could be affected, Shahvandi said.
The findings also underline the rapidity of modern warming. “It tells us about the rapid climate change,” Shahvandi said, “(the) melting of snow and ice in polar ice sheets and mountain glaciers, and the rise in sea levels.”
Kiani Shahvandi, M., & Soja, B. (2026). Climate-induced variations in the length of the day since the late Pliocene. Journal of Geophysical Research: Solid Earth, 131(3). https://doi.org/10.1029/2025jb032161
