Earth's Spin Accelerating: Scientists Predict Potential 'Negative Leap Second' by 2029

Scientists have observed that the Earth's rotation is accelerating, leading to days that are a few milliseconds shorter. While seemingly insignificant, this change could have profound implications for global timekeeping.

Currently, leap seconds are periodically added to atomic clocks to compensate for the Earth’s slowing rotation. However, if the current trend continues, experts anticipate that we may need to subtract a leap second by 2029 – a historic first. This adjustment would signify a major shift in how we synchronize human-made time with the planet's natural rhythms, underscoring the subtle but dynamic changes influencing our perception of time.

The Evolution of Earth's Day Length

The Earth typically requires approximately 86,400 seconds to complete one rotation, defining a 24-hour day. However, this duration isn't constant. Various natural phenomena, ranging from gravitational forces to internal geophysical shifts, contribute to slight variations in the Earth's rotational speed.

Historically, the Earth's rotation has decelerated gradually. For instance, during the age of dinosaurs, days were roughly 23 hours long. By the Bronze Age, they had increased in length but were still about half a second shorter than they are today. Over the long term, it is predicted that Earth might experience 25-hour days, but scientists estimate this will take another 200 million years.

Implications of the Changing Rotation

Since 2020, the Earth has been spinning faster, surprising the scientific community. According to the International Earth Rotation and Reference Systems Service (IERS), this acceleration has been consistent.

This acceleration results in shorter days, albeit by milliseconds. If this trend persists, experts suggest the need to remove a leap second from Coordinated Universal Time (UTC) by 2029. Leap seconds are conventionally added to atomic clocks to keep them aligned with the Earth's irregular rotation, acting as a bridge between atomic time and the planet's actual spin.

Up until now, leap seconds have only been added to account for the Earth's deceleration. However, with the Earth spinning faster, subtracting a second from atomic time may become necessary to maintain accuracy.

Expected Shortest Days in 2025

According to timeanddate.com, the trend of shorter days is expected to persist into 2025. Scientists have identified three specific dates when the Earth's spin is projected to be at its fastest:

• July 9, 2025
• July 22, 2025
• August 5, 2025

Reports from USA Today indicate that on August 5, the length of a day could be 1.51 milliseconds shorter than the standard 24 hours. While imperceptible to humans, this deviation is noteworthy from a scientific perspective.

Unraveling the Cause of Earth's Acceleration

The underlying cause of this recent acceleration remains unclear, and scientists are exploring several possibilities:

• Seismic activity
• Changes in the Earth's core dynamics
• Glacial rebound (the rising of land after the melting of ice sheets)
• Shifts in ocean currents or atmospheric pressure

Leonid Zotov, a researcher at Moscow State University, noted that this acceleration was unexpected. He co-authored a 2022 study on the subject but admits that no current model adequately explains the phenomenon. While fluctuations in the oceans and atmosphere may play a role, they are likely insufficient to fully account for the observed acceleration. Some researchers propose that movement within the Earth’s molten outer core could be influencing the rotational speed.

Reassurance from Scientists

Despite these unusual findings, scientists remain unconcerned. While the Earth's rotation speeding up is rare, such fluctuations are not without precedent. Over centuries, the planet still exhibits a general tendency toward gradual deceleration.

Removing a leap second in 2029 would be a technical adjustment to maintain synchronization between atomic clocks and Earth's rotation. It would not impact daily life, devices, or global operations. However, it serves as a compelling reminder of the complex natural forces influencing even fundamental concepts like time.