“Rotation” refers to an object’s spinning motion about its own axis. Earth rotates on its own axis, producing the 24-hour day relative to the Sun, with an inclination of 23.45 degrees from the plane of its orbit around the Sun.
However, days on Earth are growing slightly longer, and that change is accelerating. The reason is connected to the same mechanisms that also have caused the planet’s axis to meander by about 30 feet (10 meters) in the past 120 years.
Must read: CONSEQUENCES OF CLIMATE CHANGE – WORLD
Climate change is altering the Earth’s axis of rotation and the length of the day. The speed of rotation, which was hitherto mainly influenced by the moon, will now also depend much more on the climate. When the Earth’s ice masses melt, the way the planet rotates also changes.
How melting of polar ice has slowed down Earth’s rotation?
Earth’s rotation has slowed down because of human activity. This could have been caused by the melting of polar ice due to human-induced global warming and subsequent movement of water towards the equator.
Due to the movement of water from the pole to the equator, Earth has become slightly less spherical and more flattened. As a result, the moment of inertia of Earth, which is a measure of how spread its mass is, has increased.
The angular momentum of a spinning body, which is the product of its moment of inertia and angular velocity, is conserved unless acted upon by an external torque. Earth’s angular velocity, which is how fast it is spinning, must therefore decrease if the moment of inertia increases.
Angular Momentum = Moment of Inertia X Angular Velocity
This is the same natural law due to which when an ice skater stretches out their arms while spinning, their spinning velocity decreases.
Normally, Earth’s rotational speed decreases due to the gravitational pull of the moon over millions of years. The Earth was spinning much faster earlier.
Analysis of sediments suggested that 1.4 billion years ago Earth was completing a full rotation around its axis in only 19 hours as opposed to the 24 hours that it takes today. Even around 370 million years ago a day was only 22 hours long.
A leap second is added from time to time to the Coordinated Universal Time to account for this slowing down. The last time a leap second was added, was on December 31, 2016.
However, from 1970 onwards Earth’s rotational speed has been increasing due to some movement of fluids in its outer core. This increase in speed is superseding the slowing down of Earth’s rotational speed due to the Moon’s gravity. To account for that, it was calculated that a leap second was to be subtracted in either 2025 or 2026.
But human-induced slowing down has postponed this subtraction. Now a leap second has to be subtracted later, probably, in 2028 or 2029.
The addition or subtraction of a leap second can be problematic for telecommunications and computing. However, it doesn’t significantly impact our daily lives otherwise.
How Melting of Polar Ice Alter the Axis of Rotation?
Shifts in mass on the Earth’s surface and in its interior caused by the melting ice not only change the Earth’s rotational speed and the length of day, they also alter the axis of rotation. This means that the points where the axis of rotation actually meets the Earth’s surface move.
Researchers can observe this polar motion, which, over a longer timeframe, comes to some ten metres per hundred years. It’s not only the melting of the ice sheets that plays a role here, but also movements taking place in the Earth’s interior.
Deep in the Earth’s mantle, where the rock becomes viscous due to high pressure, displacements occur over long periods of time. And there are also heat flows in the liquid metal of Earth’s outer core, which are responsible for generating the Earth’s magnetic field and also lead to shifts in mass.
Climate change is causing the Earth’s axis of rotation to move, and it appears that the feedback from the conservation of angular momentum is also changing the dynamics of the Earth’s core. Ongoing climate change could therefore even be affecting processes deep inside the Earth and have a greater reach than previously assumed.
The major concern is how our actions are impacting significant changes in the movement of our planet. It has been showed that pumping out water by human beings from aquifers and its redistribution to the oceans resulted in a drift of Earth’s rotational pole. It is becoming clear that our actions may have more far-reaching consequences than we have previously realised.
PRACTICE QUESTIONS
QUES . Consider the following statements: UPSC PRELIMS 2025
Statement I: Scientific studies suggest that a shift is taking place in the Earth’s rotation and axis.
Statement II: Solar flares and associated coronal mass ejections bombarded the Earth’s outermost atmosphere with tremendous amount of energy.
Statement III: As the Earth’s polar ice melts, the water tends to move towards the equator.
Which one of the following is correct in respect of the above statements?
(a) Both Statements II and III are correct and both of them explain Statement I.
(b) Both Statement II and Statement III are correct but only one of them explains Statement I.
(c) Only one of the Statement II and III is correct and that explains Statement I.
(d) Neither Statement II nor Statement III is correct.
Answer – (b) EXPLANATION: Although solar flares, and associated coronal mass ejections, can bombard Earth’s outermost atmosphere with tremendous amounts of energy, most of that energy is reflected back into space by the Earth’s magnetic field. While the energy doesn’t decisively affect earth’s rotation and axis, it causes heating and expansion of the thermosphere, disrupts radio communications, and affects satellites and power grids.
