Earth’s Rotation Speed ​​Is Accelerating: Should We Be Worried?

On June 29, 2022, Earth experienced its shortest day since scientists used the atomic clock to measure its rotation rate. It made a complete turnaround 24 hours minus 1.59 milliseconds. Experts who have been setting speed records since 2020 are not worried about this one-time phenomenon.

In the very long term, however, the observed trend is the opposite: the Earth’s rotation is slowing down. Each century takes a few extra milliseconds to turn.

Astronomer Christian Bizouard was reported by our colleagues Western France, however, notes that “since 1830, we have seen a decrease in the Earth’s rotation rate and therefore an increase in the length of the day. “This trend has been inexplicably reversed for 7 years.”

In 2020, the fastest 28 days since 1930

The scientist reminds that the rotation period increases by about 2 milliseconds every century. In the short term, the speed of rotation of the earth on its axis can vary by a few milliseconds per year compared to international reference time (86,400 seconds = 24 hours x 60 minutes x 60 seconds).

To understand the evolution of Earth’s velocity, you must turn to the winds and tides. “This is a completely normal and cyclical phenomenon that we can explain and model. In particular, it was found that the rate varied seasonally within a year or two, and several events occurred […]. 80% of the changes in the Earth’s speed are related to mass transport in the atmosphere, in other words, winds.”

Likewise, tides strongly influence the planet’s rotation: “this phenomenon is strong enough to account for 10-20% of the variation in rotation period.” When we know that 72% of the Earth’s 509 million km2 surface is covered by water, we better understand how tides can deform the oceans and the Earth’s surface.

These two phenomena may hide a third, less known to scientists. Christian Bizouard explains that internal movements in the Earth, such as molten magma, can also change the Earth’s speed. The latter will currently justify a few inexplicable milliseconds. The researcher admits, however, that the community currently has “no observations of the hard core, such as those conducted in the atmosphere, that would confirm these hypotheses.”

Moreover, Christian Bizouard does not try to put everything behind climate change: “Is the Earth spinning faster because of this? We don’t know anything. To say this is pure speculation.”

A leap second

This short-term acceleration in the Earth’s rotation speed is nothing to worry about and will not “change the course of our existence”. Adjustments must be made for international chronometers. Indeed, these few small irregularities cause the rotational time to be synchronized from atomic time.” Therefore, there are adjustments made on a very specific basis to get the two back in sync.

As the French scientist explained, “Since 1972, the International Earth Rotation and Reference Systems Service regularly adds a ‘leap second’ to the end of the year at the end of June or the end of December. There have been 28 so far. The last one falls on December 31, 2016.” If the Earth continues to accelerate as it has in recent years, it is likely that the chronometers will have to erase the second – the first!

These adjustments, better known as “leap seconds”, are not without consequences for the general public. When a leap second was added in 2012, it caused numerous synchronization errors on the internet. Many services and sites (LinkedIn, Mozilla…) faced difficulties not knowing how to interpret the second attachment in their tasks.

Over the past year, most GAFAs have been on the fence about adding leap seconds: “Every time a leap second is introduced, we run into problems. Because it’s a rare event, every time it happens, it destroys society,” explains the Meta group (Facebook, Instagram, Whatsapp). Like Google, Amazon or Microsoft, the latter simply wants to “stop the use of leap seconds in the future”.

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