Earth's Days Are Stretching Due to Climate-Driven Shifts in Rotation

It might sometimes feel like the days are starting to drag on, but scientists say that this isn't necessarily all in your head.

In a new study, researchers from the University of Vienna and ETH Zurich have found that the length of days on Earth is increasing at an 'unprecedented' rate. Days are getting longer at a rate of 1.33 milliseconds per century, a pace of change faster than any other point in 3.6 million years of Earth's history. Scientists attribute this shift to human-caused climate change, which is altering the planet's rotation through rising sea levels and melting polar ice sheets.

The mechanism behind this phenomenon is akin to a figure skater extending their arms to slow their spin. As global warming accelerates the melting of ice caps and glaciers, water flows from the poles toward the equator. This redistribution of mass moves Earth's rotational inertia outward, slowing the planet's rotation like a spinning top losing speed as its weight shifts away from its center. Co-author Professor Benedikt Soja of the University of Vienna explained that natural cycles have historically influenced day length, but human activity has now accelerated this process to rates not seen since roughly 2 million years ago.

Earth's rotation has never been perfectly uniform. The moon's gravity and internal geological processes have subtly altered day length over millennia, but these changes were minor compared to the recent impact of climate change. However, Professor Soja noted that human activity is now influencing Earth's rotation more significantly than natural factors alone. The redistribution of mass from melting ice and rising oceans increases the planet's moment of inertia, causing the rotation to slow down incrementally.

While these shifts are currently imperceptible to the average person, they could have far-reaching implications for systems reliant on precise timekeeping. Even minor disruptions in Earth's rotational speed can affect GPS satellites, atomic clocks, and space navigation technologies. Professor Soja emphasized that monitoring these changes is critical to maintaining the accuracy of global systems that depend on synchronized timing.

Looking ahead, researchers predict that climate change will continue to amplify this effect. By the end of the 21st century, the impact of rising sea levels and shifting mass distribution is expected to surpass the gravitational influence of the moon. Models suggest that Earth's day could lengthen by an additional 2.62 milliseconds per century starting in the 2080s—a rate significantly higher than historical natural fluctuations.

To understand the scale of these changes, scientists turned to geological records stretching back millions of years. They analyzed the chemical composition of fossilized shells from ancient single-celled organisms called benthic foraminifera. These microscopic remains preserved clues about past sea level fluctuations, which were then used in a physics-informed machine learning model. The data revealed that natural climate cycles over 3.6 million years had caused variations in day length, but nothing comparable to the rapid changes observed since the 21st century.

The study highlights a stark contrast between natural and human-induced climate shifts. While Earth's rotation has historically slowed during periods of extreme natural warming—such as when Greenland was ice-free two million years ago—the current pace of change is faster and more severe. This acceleration, driven by greenhouse gas emissions, underscores the unprecedented scale of modern climate change compared to past natural cycles.

The findings serve as a reminder that human activity is now shaping planetary processes once thought to be governed solely by natural forces. As sea levels rise and ice sheets continue to melt, the Earth's rotation will slow further, altering the fundamental rhythm of our planet in ways that could impact both scientific systems and broader ecological dynamics.