The story so far: On June 29, 2022, the Earth completed its axial spin at a record speed, shortening the day by 1.59 milliseconds. According to reports, this new record could indicate the heavenly body’s move towards a faster rotational axis in the short run but it could slow down over a period.
Tech giants like Meta have apparently raised an issue as it could necessitate the adding of a leap second, which may in turn affect software that has been programmed to display time a certain way. In fact, the Earth does periodically slow down and speed up in its rotation about its axis. This is a wavelike change.
Reasons for change in the Earth’s rotational speed
There are several factors that have been linked to the change in the Earth’s rotation rate ranging from the transfer of angular momentum from its interior to the outside to the oxygenation of its atmosphere. Anything that changes the composition and distribution of material on the Earth’s surface can also have this effect. Dr. Binod Sreenivasan, Head of the Department of Earth Sciences at IISc Bengaluru, explains one of the dominant effects: “The Earth’s magnetic field is produced by convection that occurs in the outer core, creating waves. These are called torsional waves. They originate from the outer core or from the fluctuations of buoyancy in the inner molten core. We can think of these as concentric cylinders that oscillate back and forth, all the way from the inner core to the mantle, creating waves that travel outward…this has been correlated to the length of day for a century now.”
He added that in the recent past, the Earth’s rotation has varied between one or two milliseconds and this phenomenon has been termed normal.
Speaking of alternate reasons for this change, he said, “To some extent, tidal waves and tidal motion can also contribute to the variations in the length of night and day and can indirectly be associated with climate change.”
Another plausible reason could be the melting of glaciers and polar ice caps that result in a change of mass distribution on the surface or interior of the Earth. If ice melts rapidly or continuously in a particular region of the planet, it could cause a tip in balance. The Earth also wobbles because of the fact that its axis of rotation is tilted with respect to the geographical axis. This is called the Chandler wobble, named after American astronomer Seth Carlo Chandler who also discovered the effect, and a change in this angle can cause a variation in rotation time too.
Can the study of core mechanics predict such variations in the future?
“To an extent, we can predict because we have enough records of the past to tell between what upper and lower bounds length of day variation can occur. It is very unlikely to get extremely abnormal behaviour that should be a cause of concern,” the professor clarified.
Is this change in speed a cause for worry?
“It is not a serious matter because oscillations happen in either side of zero. If there is a minus of 1.59 [milliseconds] now, in about 10 to 15 years, it can also be plus 1.8,” Dr. Sreenivasan said. While there may be a reduction in the length of duration of a day, it is possible that in the future, there could be an increase that can compensate for the same. Concern arises when oscillation happens only in one direction which is unlikely to happen given the past record of these variations “because the Earth’s magnetic field is dynamic.”
However, there could be cause for concern if glacial melting occurs rapidly on one side of the Earth. This could tip the balance and affect the Earth’s rotational speed. But the professor noted that “the strongest link to the length of day variations happens from the core of the Earth...other mechanisms are all secondary. The strongest correlation we find is from torsional oscillations and when the theory is compared to the model, it is accurate…there is more than one way to prove this theory.”
Is this change an indicator of the Earth’s behaviour in the long run?
Reports claim that the new record could mean acceleration now but the earth could decelerate in the long run. However, the professor pointed out that in 1910, an acceleration occurred, followed by another in 1970 or 1980. This was then followed by deceleration. Such oscillations can occur at any time and therefore do not point towards a one-way progression or regression in a period of time.