The planet’s natural rhythm is changing—and timekeepers around the world are watching closely. Earth is rotating faster than it used to, prompting scientists and international timekeeping authorities to consider an adjustment that has never been made before: subtracting a second from Coordinated Universal Time (UTC).
This possible measure, referred to as a “negative leap second,” would be unprecedented in human history. Although leap seconds have been inserted to align clocks with Earth’s somewhat inconsistent rotation, removing one poses intricate issues for technology, communications, and worldwide systems that depend on exact timing.
For many years, measuring time has involved adjusting for the Earth’s inconsistent rotation by occasionally inserting an additional second to UTC, the international benchmark for official time. These added leap seconds ensure that atomic time remains synchronized with the real duration of a day, which is affected by the Earth’s dynamics. However, recent findings indicate a change: rather than decreasing its speed, the Earth is now spinning marginally quicker on average.
This unexpected acceleration in Earth’s spin has surprised scientists. Typically, Earth’s rotation gradually slows over time due to tidal friction caused by the gravitational pull of the Moon. However, fluctuations in the planet’s core, changing atmospheric patterns, and redistributions of mass from melting glaciers and shifting oceans can all influence the planet’s rotational speed. Recent measurements indicate that some days are lasting slightly less than the standard 86,400 seconds—meaning Earth is completing its spin in less time than it used to.
As this trend continues, the time discrepancy between Earth’s rotation and atomic clocks could grow to the point where a negative leap second becomes necessary to keep clocks in sync with the planet’s actual motion. This would involve subtracting a second from UTC to realign it with Earth’s day.
Implementing such a change is no small matter. Modern technology systems—from GPS satellites to financial networks—depend on extreme precision in timekeeping. A sudden subtraction of a second could introduce risks in systems that aren’t programmed to handle a backward step in time. Software systems, databases, and communication protocols would all need to be carefully updated and tested to accommodate the change. Unlike the addition of a second, which can often be handled by simply pausing for a moment, taking away a second requires systems to skip ahead—something many infrastructures aren’t equipped to do without hiccups.
The worldwide community responsible for time measurement, encompassing entities such as the International Bureau of Weights and Measures and the International Earth Rotation and Reference Systems Service, is currently assessing the optimal strategy to tackle this matter. The difficulty is in finding a balance between the requirement for scientific precision and the technical realities of our rapidly evolving digital environment.
This isn’t the first time timekeeping has faced disruption from Earth’s irregular behavior. Leap seconds have caused minor outages in the past, particularly in systems that weren’t prepared for them. But because leap seconds have always been added, not subtracted, there are no established precedents or protocols for a negative leap second. That makes the current situation both novel and delicate.
The reason leap seconds exist at all stems from the difference between atomic time—which is incredibly consistent—and solar time, which is influenced by the Earth’s actual rotation. Atomic clocks, which use the vibrations of atoms to measure time, don’t vary. In contrast, solar time fluctuates slightly based on Earth’s orientation and rotation speed. To keep our time system aligned with the natural day-night cycle, leap seconds have been introduced as needed since the 1970s.
Now, Earth’s faster spin is challenging the very convention that time has flowed according to for decades. Though the differences involved are minuscule—fractions of a second—they add up over time. If left uncorrected, the misalignment between UTC and solar time would eventually become noticeable. It’s an invisible issue to most people but critical to systems that depend on nanosecond accuracy.
The question now is not only when a negative leap second might be required but also how to implement it without widespread disruption. Engineers and researchers are developing models and simulations to test how systems might react. At the same time, conversations are taking place at the international level to determine whether the current leap second system is still sustainable in the long term.
In fact, there has been growing debate in recent years about whether leap seconds should be abandoned entirely. Some argue that the complexity and risk they introduce outweigh the benefit of keeping atomic time aligned with solar time. Others believe that preserving that alignment is essential for maintaining our connection to natural time cycles, even if it requires periodic adjustments.
The discussion also reflects a broader philosophical question about time itself: should we prioritize precision and consistency above all else, or should our timekeeping reflect the natural rhythms of the planet? Earth’s speeding rotation is forcing scientists and policymakers to confront this question in real time.
Examining the future, it seems probable that additional studies will shed light on the reasons and the length of this speeding up. Should this pattern persist, the global community might actually experience its inaugural negative leap second—an unprecedented event highlighting the Earth’s dynamic character and the complex mechanisms humans have devised to gauge it.
Until then, timekeepers are on alert, scientists are crunching the numbers, and engineers are preparing for a shift that could ripple across the global digital landscape. One second may seem small, but in a world that runs on precision, it could make all the difference.
