Earth’s Spinning Speed Increases: Days Shorter This Summer

Washington, DC — Earth is spinning faster this summer, causing days to be slightly shorter and capturing the attention of scientists worldwide. On July 10, 2025, the day lasted 1.36 milliseconds less than the usual 24 hours, according to data from the International Earth Rotation and Reference Systems Service and the US Naval Observatory.

More exceptionally short days are expected on July 22 and August 5, with predictions indicating they will be 1.34 and 1.25 milliseconds shorter than 24 hours, respectively. A full rotation of Earth typically takes 86,400 seconds, but various factors lead to slight irregularities in this duration.

Factors such as the gravitational pull of the moon, seasonal atmospheric changes, and the influence of Earth’s liquid core all contribute to the variability in Earth’s rotation. Although these differences, usually measured in milliseconds, do not affect daily life, they can impact technology like computers and satellites.

“These discrepancies, even if they appear minor, could lead to complications similar to the Y2K issue in the past,” warned an expert. Atomic clocks, measuring atomic oscillations with extreme precision, dictate Coordinated Universal Time (UTC), which is how most electronic devices synchronize.

Astronomers track Earth’s rotation through satellite technology and can detect tiny differences between atomic time and Earth’s actual rotation. The previous record for the shortest day occurred on July 5, 2024, lasting 1.66 milliseconds less than 24 hours.

Duncan Agnew, a professor emeritus at the Scripps Institution of Oceanography, noted, “We’ve seen a trend toward slightly faster days since 1972, but there are fluctuations.” In 1972, the International Earth Rotation and Reference Systems Service introduced mandatory “leap seconds” to UTC to align it with Earth’s rotation. Since then, nine leap seconds were added, yet none have been added since 2016.

In 2022, a proposal to retire leap seconds by 2035 was made, with the potential for a negative leap second if Earth continues to spin faster. “The likelihood of having a negative leap second by then is about 40%,” Agnew stated.

The moon and tides significantly impact Earth’s rotation speed. As the atmosphere changes with the seasons, Earth generally spins faster in summer. However, the liquid core of the planet is slowing down, while the solid Earth accelerates. This is a complex interplay that scientists study to predict short days.

Judah Levine, a physicist at the National Institute of Standards and Technology, affirmed, “These fluctuations can correlate from day to day, but predictions get uncertain as intervals lengthen.” This growing trend of shorter days raises alarms about how a negative leap second could complicate technology that depends on precise timekeeping.

Concerns arise because positive leap seconds have continued to pose challenges even after decades of use, creating higher risks if a negative leap second were to be implemented. Levine compared the potential technological impacts of a negative leap second to the anxiety surrounding the Y2K issue.

Interestingly, climate change has a paradoxical role, affecting Earth’s rotation. A study led by Agnew indicated that melting ice in Antarctica and Greenland is influencing Earth’s spin, potentially countering the forces that lead to faster rotation. “If that ice had not melted, we would have already faced a negative leap second,” Agnew explained.

Research suggests that future climate impacts could become more dominant. “By the end of this century, continued greenhouse gas emissions could overshadow the moon’s influence on Earth’s rotation,” warned Benedikt Soja, an assistant professor at the Swiss Federal Institute of Technology.

As Earth spins faster, scientists continue to monitor changes, keeping future technological implications in mind. “It remains within reasonable variability for now,” Soja concluded, though uncertainty about long-term trends persists.