Recently, some media reported that in 5 years, that is, in 2029, 1 minute or only 59 seconds.
This claim comes from a study by scientists at the University of California, San Diego, published in the journal Nature.
Scientists have found that due to global warming, the Arctic and Antarctic ice sheets are melting on a large scale, changing the shape of the Earth and causing the Earth's rotation to slow down faster than before. This change could trigger a global timing crisis within five years, such as massive disruptions to computer communications and telecommunications networks.
Image source: Screenshot of the website
In fact, this statement is not accurate, and the correct statement would be that in 2029, a certain 1 minute could be shortened to 59 seconds, and the melting of the ice sheet delays the arrival of this day.
What's going on here? Why is 1 minute reduced to 59 seconds? Isn't time fixed? How will this affect our lives?
Our timing system
Although time seems to pass evenly, we have actually been adjusting for decades – inserting a leap second every few years. In order to better understand this problem, we first need to understand our timing system.
In order to determine time, there are three common time systems nowadays, which are:
以地球自转周期为基准的世界时(Universal Time,UT1)
以地球绕太阳公转周期为基准的历书时(Ephemeris Time,ET)
以原子内部电子能级跃迁发射的电磁振荡频率为基准的原子时（International Atomic Time，法语：Temps Atomique International, TAI）
Universal Time (UT1) is a standard of time determined by recording the time it takes for the Earth to rotate once as a day. It divides the time scale based on the change in the angle of the Earth relative to the flat Sun. World time plays an important role in the fields of navigation and navigation, as well as in the fields of astrometry and astronomical geodesy.
However, because the speed of the Earth's rotation is not constant, the stability of universal time is insufficient to fully meet the needs of modern scientific research and technology applications for extremely accurate time, such as astronomical observations and global navigation satellite systems (GNSS).
In order to meet the practical needs of higher precision, scientists have introduced atomic time. Specifically, atomic time is achieved through atomic clocks, which use the period of electromagnetic oscillations inside the atom to keep time, which is very stable.
Therefore, atomic time has extremely high accuracy and stability, and can provide extremely accurate time standards, so it is widely used in scientific research, navigation systems, communication networks and other fields.
Cesium atomic clock Image Credit: Wikipedia
In 1967, the 13th International Conference on Weights and Measures decided to change the definition of seconds from astronomical seconds to atomic seconds, and set the duration of the 9192631770 cycles of radiation corresponding to the interference-free superfine energy level transition of the cesium-133 atom as 1 second, that is, the duration of the radiation vibrations emitted by the cesium-133 atom 9192631770 times was set to 1 second, which is called the SI second.
This decision marked the formalization of atomic time and laid the foundation for the subsequent development of a time measurement system.
It is worth mentioning that in order to achieve the independent calibration of our national standard time, the scientists represented by researcher Zhang Shougang of the National Time Service Center of the Chinese Academy of Sciences have been rooted in the west for a long time, willing to be lonely, and have tackled key problems for more than ten years, and successfully developed a high-stability and continuous operation of the cold atomic cesium fountain reference clock, reducing the deviation between the continental standard time and the international standard time from 100 nanoseconds to less than 5 nanoseconds.
In the Space Strontium Atomic Optical Clock Laboratory of the National Time Service Center of the Chinese Academy of Sciences, the measuring instrument displays the relevant experimental signals. Photo by Xinhua News Agency reporter Zhang Bowen
Why does one minute become 59 seconds?
The worldtime with the Earth's rotation as a reference has always been one of the important parameters for the generation of international standard time. The day is divided into 24 hours, 1 hour and 60 minutes, and one minute and 60 seconds, and it is important that the world time reflects the angle of rotation of the Earth relative to the cosmic background.
The use of atomic time is a very accurate and immutable way to define time, but it also has a troubling consequence: atomic time does not quite match the world time defined by the Earth's rotation.
Difference between atomic time and universal time. Image source: Ref. [1]
Over the centuries, the increasing stability of time measurements has allowed us to see that the Earth's rotation speed is not constant, which can create a difference between atomic time and universal time.
To accommodate both needs, the Coordinated Universal Time (UTC) system was introduced. When the difference between the time of the international atomic time and the universal time reaches 0.9 seconds, the Coordinated Universal Time (UTC) needs to be adjusted, i.e. increased or subtracted by 1 second to get as close to the universal time as possible, which is known as a leap second (negative leap second, 59 seconds for the last minute; positive leap second, 61 seconds for the last minute). This universal time with leap seconds added is Coordinated Universal Time, also known as Coordinated Universal Time, and is currently the most widely used time system.
Since the official use of UTC in 1972, the Earth's rotation has been slowing down, and 27 leap seconds have been added to UTC, all of which are positive leap seconds. However, since mid-2020, the Earth's rotation rate has been accelerating.
Therefore, scientists estimate that in 2029, humans may need to reduce the "negative leap second" by 1 second for the first time, corresponding to only 59 seconds for 1 minute, to keep the atomic clock time in sync with the Earth's rotation cycle.
Why is the Earth's rotation speed not constant?
On the millennial time scale, changes in the Earth's rotation speed are influenced by three geophysical processes.
First, the friction between the seawater and the seafloor gradually consumes the kinetic energy of the Earth's rotation, thus slowing down the Earth's rotation, which is known as the tidal effect.
Second, due to the rebound after the ice age, the shape of the Earth changes and becomes flatter, causing the Earth's moment of inertia to change and reduce its rotation speed. This is similar to how a skater spins by extending their arms flat to the sides of their body to slow down the rotation as they spin.
Finally, some processes within the Earth, i.e., the interaction and interaction between the Earth's core and its outer layers (mantle, crust), such as changes in the geomagnetic field and mantle convection, can also cause changes in the Earth's rotation speed.
According to data from the National Aeronautics and Space Administration (NASA) and the International Earth Rotation and Reference System Service (IERS), the Earth's rotation is indeed slowing down. Studies have shown that the Earth's rotation period increases by about 1.8 milliseconds per century. While this may seem like a small change, the cumulative effect is significant over a long period of time.
For example, there is a significant difference between the time of a solar eclipse recorded by ancient astronomers and the time we calculate today. The time of the solar eclipse observed 2,500 years ago (around the Spring and Autumn Period and the Warring States Period) has a clock error of about 4 hours compared to modern clocks.
Originally, scientists expected that the slowdown in the Earth's rotation would lead to the first "negative leap second" in 2026 due to these geophysical processes.
However, satellite measurements show that since 1986, the ice sheets of Greenland and Antarctica are melting at an accelerated rate as global warming intensifies. This phenomenon has led to an acceleration in sea level rise, further slowing the Earth's rotation. Due to the dual effects of melting ice sheets and rising sea levels, the Earth's moment of inertia increases and its rotation speed becomes slower, delaying the arrival of negative leap seconds.
The polar ice melts and moves towards the equator, slowing down the Earth's rotation. Image source: Ref. [3]
What are the effects of leap seconds?
Leap seconds are usually implemented at 23:59:60 on June 30 or December 31 UTC. The adjustment of leap seconds has little direct impact on daily life, and people often do not feel the changes brought about by leap seconds.
However, leap seconds have an important impact on technical systems and applications that rely on precise time synchronization, such as computers, finance, aerospace, and other fields.
For example, the addition or deletion of leap seconds requires global synchronization, which poses a challenge to the time management of computer systems.
In 2012, a number of large websites experienced a brief service interruption due to a time synchronization error, which caused the server to crash. In 2015, when leap seconds came again, engineers fixed some of the problems that occurred in 2012, but found new ones. For another example, every time a leap second is adjusted, the GNSS system needs to update the time data to ensure the accuracy of timing. Failure to adjust in time may result in inaccuracies in navigation messages.
Unlike the traditional leap second, which adds one second, the unprecedented negative leap second will introduce new challenges and uncertainties to many systems that rely on precise time synchronization. Computer and network systems, financial systems, etc., are often designed to handle the increasing positive leap seconds, but may not be adequately prepared to deal with the decreasing negative leap seconds. Scientists are calling for concerted efforts to fully prepare for the implementation of negative leap seconds to ensure the stability and security of the global technology system.
The stock copyright picture, reprinting and using may cause copyright disputes
Although leap seconds were originally intended to keep UTC in sync with the Earth's rotation time UT1, the adjustment of leap seconds, especially the potentially negative leap seconds, is increasing the complexity of time synchronization systems. It has been proposed to implement larger corrections, such as intercalary minutes and intercalary hours, to extend the adjustment time to 100 years and 1,000 years; It has also been suggested to stop the correction and at the same time publish the growing time difference between Universal Time and International Atomic Time.
The 27th International Conference on Weights and Measures in 2022 decided to abolish leap seconds and replace them with leap minutes no later than 2035, that is, to allow the difference between international atomic time and universal time to be less than 1 minute. It also called for consultations on a new formula that would last "UTC" for at least 100 years.
As technology evolves, new time synchronization technologies will emerge, such as more accurate optical clocks and smarter network time protocols, which may provide new ways to solve the leap second problem.
bibliography
[1] Tavella, Patrizia, and Jerry X. Mitrovica. "Melting ice solves leap-second problem—for now." (2024).
[2] Agnew, Duncan Carr. "A global timekeeping problem postponed by global warming." Nature 628.8007 (2024): 333-336.
[3] Gibney, Elizabeth. "Climate change has slowed Earth’s rotation—and could affect how we keep time." Nature 628.8007 (2024): 243-244.
Planning and production
Author丨Ph.D. student in Physical Chemistry at Denovo
Review丨Yin Dongshan, Associate Researcher, National Time Service Center, Chinese Academy of Sciences
Planning丨Wang Mengru
Editor-in-charge丨Wang Mengru
Reviewer丨Xu Lai Linlin