This summer, Earth is spinning faster than usual, leading to shorter days and igniting interest among scientists and timekeepers. On July 10, 2023, Earth recorded its shortest day yet, lasting 1.36 milliseconds less than the standard 24 hours. According to data from the International Earth Rotation and Reference Systems Service and the US Naval Observatory, which has been compiled by timeanddate.com, even shorter days are expected on July 22 and August 5, projected to be 1.34 and 1.25 milliseconds shorter than the typical 24-hour day.
The length of a day is defined by the time it takes for Earth to complete one full rotation on its axis, typically 24 hours or 86,400 seconds. However, this rotation is not perfectly uniform and can vary slightly due to several factors. These include the gravitational pull of the moon, seasonal atmospheric changes, and the fluid dynamics of Earth's liquid core. Consequently, each day can be marginally shorter or longer than 86,400 seconds — usually by just a few milliseconds. While these discrepancies might not significantly impact daily life, they can have considerable implications for technology, such as computers, satellites, and telecommunications.
To track these minor time deviations accurately, scientists utilize atomic clocks, which were first introduced in 1955. Atomic clocks measure time by counting the oscillations of atoms in a vacuum chamber, providing unparalleled precision. This precise timekeeping gives rise to UTC, or Coordinated Universal Time, a global standard based on approximately 450 atomic clocks. It is the benchmark to which all electronic devices, including phones and computers, are synchronized.
Interestingly, July 5, 2024, marked the shortest day recorded since the inception of atomic clocks, clocking in at 1.66 milliseconds shorter than 24 hours. According to Duncan Agnew, a professor emeritus of geophysics at the Scripps Institution of Oceanography, Earth has been gradually spinning faster since 1972, albeit with fluctuations. “It's akin to observing the stock market, where you see both long-term trends and short-term variations,” he explained.
In 1972, due to a significant delay in Earth's rotation relative to atomic time, the International Earth Rotation and Reference Systems Service introduced the concept of the leap second to UTC. Similar to a leap year, which adds an extra day to February every four years, leap seconds are essential for maintaining synchronization between atomic time and Earth's rotation. Since 1972, a total of 27 leap seconds have been added, yet the frequency of these additions has diminished as Earth's spin accelerates. Remarkably, no leap seconds have been added since 2016.
In 2022, the General Conference on Weights and Measures voted to phase out the leap second by 2035. However, if Earth's acceleration continues, Agnew suggests that we might eventually need to remove a second from UTC. “There has never been a negative leap second,” he noted, “but the probability of having one before 2035 stands at around 40%.”
According to Agnew, the immediate reasons behind Earth’s increased spin include the moon's gravitational effects and tidal forces. When the moon is over the equator, Earth spins slower, while it speeds up when the moon is at higher altitudes. Additionally, during summer, atmospheric changes contribute to a natural increase in Earth's rotational speed. The laws of physics dictate that the overall angular momentum of Earth and its atmosphere must remain constant, resulting in the planet compensating for the atmospheric slowdowns.
Interestingly, climate change also plays a role in Earth's rotation. While global warming poses severe risks to the planet, it inadvertently counteracts some forces that speed up Earth’s spin. A study published by Agnew reveals that melting ice from Antarctica and Greenland contributes to oceanic changes that slow down Earth’s rotation, akin to a skater adjusting their spin by tucking in or extending their arms. According to NASA, meltwater from these ice sheets has contributed to a third of global sea level rise since 1993.
Research led by Benedikt Soja from the Swiss Federal Institute of Technology indicates that if the current trends in climate change continue, the effects may become even more significant. By the end of the century, in a pessimistic scenario, these climate impacts could surpass the moon's influence on Earth’s rotation. For now, scientists remain cautiously optimistic, suggesting that the current trend of faster spinning may be within natural variability.
In conclusion, while the phenomenon of Earth spinning faster and the resultant shorter days may seem trivial, the implications are profound. As technology becomes increasingly reliant on precise timekeeping, the potential for issues like negative leap seconds could pose significant challenges, much like the Y2K problem. Understanding these shifts in Earth's rotation not only helps us keep time accurately but also sheds light on broader climatic and astronomical processes affecting our planet.
