Time is traditionally measured by the rotation of the Earth. However, since the middle of the last century, there has been an even more precise way to track the passage of time – with so-called atomic clocks. They measure time based on the vibration of atoms.
Because the speed at which the Earth rotates is not constant, the measurements of atomic clocks and those based on the rotation of the Earth differ slightly. The Earth normally rotates a little slower, which is why a leap second is added to the time every so often.
A day, June 30 or December 31, then lasts one second longer than normal, in order to equalize atomic time and solar time. Since the introduction of this system in 1972, this has happened 27 times. Because the change in the speed at which the Earth rotates is not regular, the introduction of leap seconds is also not regular.
Earth spins faster
However, something special is happening now. Due to changes in the Earth’s core, the planet has been rotating slightly faster than normal in recent years. As a result, a negative leap second will soon be needed for the first time. A day is therefore one second shorter.
What exactly happens in the Earth’s core is still a mystery to scientists, and what exactly causes the Earth to rotate faster is therefore unknown. But it is certain that it will happen. Therefore, there should be a negative leap second around 2026.
Melting Arctic ice
But because of the melting of the ice caps, it will take longer before that correction is necessary. Because the ice at the North and South Poles is melting and large amounts of water are flowing towards the equator, the rotation of the Earth is slowed down slightly, American scientist Duncan Agnew noted.
That is why it will take longer, probably until 2029, before the introduction of the negative leap second is necessary. Global warming now also affects the measurement of our time.
The impact of the melting of the polar ice caps “has been significant enough to noticeably and unprecedentedly affect the rotation of the entire Earth,” Agnew told CNN. “To me, the fact that humans have changed the rotation of the Earth is crazy.”
So the melting of the polar ice has an impact, but not enough to completely undo the unique acceleration of the Earth’s rotation. “No one expected that the Earth would be moving so fast that we would have to use a negative leap second,” says the scientist.
Computer systems
“A second may not seem like much.” says Agnew, but according to the scientist the influence is still great, because many computer systems that depend on accurate time registration must be adapted to the new situation.
Many systems are designed for adding a leap second, something that has happened regularly in recent decades, but not for subtracting a second – which has never happened before.
We won’t know for sure whether this will lead to major problems until around 2029 – when exactly the introduction of the negative leap second will be necessary – again due to the unpredictability of the changes in the rotating Earth – it can only be said with certainty six months in advance.
By the way, the international community decided in 2022 to abolish the system of leap seconds from 2035. Scientists are looking for a better alternative.
Leap year
Leap years work a little differently than leap seconds. In leap years – like this year – the year lasts one day longer. That happens once every four years. This is not a correction of a change in the speed at which the earth is moving. Leap years involve compensating for the difference between a calendar year (365 days) and the duration of one revolution of the Earth around the sun (365 days and approximately six hours).
If leap years were not used, this would mean that eventually the seasons would no longer correspond to the months in which we are used to them.
