Climate Change Alters Earth’s Spin, Extends Day Length, and Shifts Rotational Axis, Study Finds

The Earth’s rotation and orientation are being affected by human-induced climate change, according to recent research. Although these changes are subtle at first, they could eventually have significant consequences, such as necessitating negative leap seconds, disrupting space travel, and influencing the Earth’s inner core.

A day on Earth typically lasts around 86,400 seconds, but the exact duration of a complete rotation can fluctuate by fractions of milliseconds each year due to various factors, including tectonic plate shifts, the inner core’s rotation, and the gravitational pull of the moon. Now, scientists are realizing that climate change is another factor that will increasingly impact the Earth’s spin.

Over the past few decades, the rapid loss of ice in polar regions, especially in Greenland and Antarctica, has contributed to rising sea levels. The majority of this additional water accumulates near the equator, causing the Earth to bulge slightly at the middle. This redistribution of mass slows the planet’s rotation because more weight is positioned farther from the Earth’s center, similar to how a figure skater slows down by extending their arms.

In a new study published on July 15 in *PNAS*, researchers used an advanced AI program that integrates real-world data with physical laws to predict how the Earth’s rotation will change over time. The findings support a study published in March, which suggested that Earth’s days will lengthen in the future. However, the new AI model provided more precise estimates of how these changes will unfold.

The same research group also published another study on July 12 in *Nature Geoscience*, revealing that the increased water near the equator is shifting the Earth’s axis of rotation, causing the magnetic poles to move farther from the axis each year. This effect has likely been occurring for at least three decades, but the new study predicts that the axis will shift even more than previously estimated.

“We humans have a greater impact on our planet than we realise,” said Benedikt Soja, a geodesist at ETH Zurich and co-author of both studies, in a statement. “And this naturally places great responsibility on us for the future of our planet.”

Slowing Rotation

Earth’s days have not always been 24 hours long. Around a billion years ago, a day on Earth may have lasted only 19 hours before gradually lengthening to the 24 hours we experience today. This change occurs on various timescales; for example, in 2020, Earth was rotating faster than at any point since 1960, but it slowed again in 2021, despite the shortest recorded day occurring in June 2022.

Generally, Earth’s rotation has been slowing over millennia, primarily due to lunar tidal friction, where the moon’s gravitational pull on the oceans drags water away from the poles, lengthening days by about 2.3 milliseconds every century. The new research indicates that climate change is currently lengthening days by about 1.3 milliseconds per century. Based on current global temperature models, this could increase to 2.6 milliseconds per century by the end of the 21st century, potentially making climate change the dominant influence on Earth’s spin.

Potential Consequences

One likely outcome of longer days is the potential need to introduce negative leap seconds, where a second is occasionally removed from the calendar to account for the lengthening days, similar to the concept of leap years. According to the March study, this might need to begin as soon as 2029, to adjust for the lengthened days accumulated over millennia.

In the past, scientists have speculated that implementing negative leap seconds could disrupt the timekeeping systems of computers and smartphones. However, there is debate over how significant this issue might actually be.

The researchers also noted that changes in Earth’s rotation could affect space travel. “Even if the Earth’s rotation is changing only slowly, this effect has to be taken into account when navigating in space — for example, when sending a space probe to land on another planet,” Soja said. He emphasized the importance of closely monitoring these changes.

Additionally, the team warned that shifts in Earth’s rotational axis might influence the rotation of the Earth’s inner core, potentially accelerating the lengthening of days. However, this interaction remains largely speculative and requires further study.

As we continue to alter the planet’s climate, the consequences for the Earth’s rotation and orientation could be profound, highlighting the need for further research and monitoring to fully understand and mitigate these impacts.