According to a study, climate change has slowed Earth’s rotation and could affect timekeeping

Posted 30 Apr 2024

2 min read

Earth rotates on its axis relative to the Sun every 24 hours mean solar time, with an inclination of 23.45 degrees from the plane of its orbit around the Sun.

Earth’s rotation is affected by three major geophysical processes -
- Tidal dissipation: Friction between ocean water and the sea floor — both in shallow seas and in deep-ocean — has progressively slowed Earth’s rotation.
- Earth’s core: Changes in the flow of currents in the molten outer core affecting its spin.
- Glacial melt: As polar glaciers melt, the water mass gets redistributed throughout the oceans, pooling most noticeably around the equator.
  - It changes the shape of Earth, making it flatter and slows down its rotation speed.

Findings of the study:
- Earth’s rotation is speeding up in recent years due to changes in its core, however, melting of polar ice mass due to climate change have decelerated such speeding up.
- To keep clocks in sync with the Earth’s rotation, speeding up of Earth’s rotation would have necessitated addition of a negative leap second in two years’ time.
  - However, climate change has delayed such addition by another three years, to 2029.

Historically, Coordinated Universal Time (UTC) is followed as time standard, in which a day lasts 86,400 seconds (24 hours * 60 minutes * 60 seconds).
- However, average length of a day depends on Earth’s rotation speed.
In case of fluctuations in Earth’s rotation speed, leap seconds are added to UTC.
- A negative leap second is subtracted in case of slowing of Earth’s rotation while a positive leap second is added to compensate for speeding up of Earth’s rotation.

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