A new study highlighted by Forbes (full article available to subscribers) reports that Earth’s rotation is slowing at a rate unmatched over the past 3.6 million years. According to researchers from the University of Vienna and ETH Zurich, the current increase in the length of a day is occurring faster than at any other period covered by their geological record, raising new questions about the relationship between climate change and planetary dynamics.
Earth’s rotation naturally slows over time due to tidal friction caused by the Moon’s gravitational pull. This process gradually transfers energy from Earth’s rotation to the Moon’s orbit, causing days to become slightly longer. However, the new research suggests that recent changes are being amplified by a different factor: the rapid melting of polar ice sheets and glaciers.
As ice melts, water moves from high-latitude regions toward the oceans, redistributing mass around the planet. This redistribution alters Earth’s moment of inertia, producing an effect similar to a spinning skater extending their arms and slowing their rotation. The researchers estimate that the current rate of day-length increase is approximately 1.33 milliseconds per century, making it the fastest long-term slowdown identified in the study.
To reconstruct Earth’s rotational history, the team analyzed fossil benthic foraminifera preserved in deep-sea sediments. These microscopic marine organisms record climatic cycles influenced by variations in Earth’s orbit and rotation. By combining geological data with machine-learning techniques, the researchers created a detailed record of changes in day length stretching back 3.6 million years.
The findings also help explain an apparent contradiction in recent observations. While some of the shortest days ever recorded have occurred since 2020, these short-term fluctuations are driven by complex interactions involving Earth’s core, atmosphere, and oceans. The study focuses instead on long-term trends that unfold over centuries and millennia.
The research highlights the growing influence of climate-driven changes on planetary processes. While the increase in day length remains tiny and imperceptible in everyday life, the study demonstrates that melting ice sheets are affecting not only sea levels and weather patterns but also the rate at which Earth rotates through time.