Atomic clocks, combined with precise astronomical measurements, have shown that the length of the day on Earth is increasing. Scientists don’t know why this happens.
Over the past few decades, the rotation of the Earth around its axis has accelerated. However, since 2020, this constant acceleration has been replaced by a slowdown. The days are getting longer again, and the reason for this is still a mystery. The increase of the day, even imperceptibly, by fractions of a second, may in the future have, among other things, effects on timekeeping, navigation systems such as GPS and other technologies.
In June 2022, a record was set for the shortest day in the last half century. But despite this, since 2020, the constant acceleration has curiously been replaced by a slowdown.
For millions of years, the Earth’s rotation has slowed down due to tidal effects. This process increases the length of each day by about 2.3 milliseconds every century. A few billion years ago, an Earth day lasted only about 19 hours.
During the last 20,000 years, another process has also been at work, accelerating the Earth’s rotation. As the last ice age ended, the melting of the polar ice sheets relieved surface pressure, and the Earth’s mantle began to move steadily toward the poles. This shortens the day by about 0.6 milliseconds every century.
Since the 1960s, scientists have begun to get very accurate estimates of the speed of the Earth’s rotation. Comparison of these estimates with the indications of atomic clocks showed that the length of the day was constantly decreasing.
However, if you remove the fluctuations in the rotation speed that occur due to tides and seasonal effects, it becomes clear that since 2020 the trend has changed from a short day to a long one. This change is unprecedented in the last 50 years.
The reasons for this are unclear. The mysterious change in the speed of the planet’s rotation is thought to be related to a phenomenon called the Chandler wobble, a slight tilt of the Earth’s axis of rotation with a period of about 430 days.
There is also an opinion that these may be long-term tidal effects, working in parallel with other periodic processes and causing a temporary change in the speed of the Earth’s rotation.