After a few years of acceleration, suddenly the Earth is now slowing down. For the first time in 7 years, the average day length became longer in 2023. Meanwhile, new forecasts suggest that March 2025 will include the longest day since March 2019. As reported by TimeandDatethe latest data provided byInternational Earth Rotation and Reference Systems Service show that Earth is slowing down, and one day in 2024 lasts a little longer than any day since 2019.
IERS even predicts that the length of a day could reach up to +1.63 milliseconds over 24 hours by March 2025, which would be the longest day on record for 5 years.
Leap Second and Drop Second
A millisecond or 2 might not seem like muchbut given that today’s technological society depends on the digital timethose milliseconds accumulate, requiring a “Leap Second” (“leap second”) or, in theory, a “Drop Second“, to bring everything back into sync.
The rapid rotation of the Earth has consequences because, for example, if the Earth rotates faster, it will arrive at the same position a little sooner: among other things, if GPS satellites do not take the rotation speed into account, their positioning data can quickly become unusable.
The Earth’s slowdown will be good news for international time keepers because a “Drop Second,” unlike a “Leap Second” has unknown consequences for the interconnected world. Among the causes scholars also report climate change, with the thawing of the ice which could slow down the rate of rotation of the Earth.
The study in Nature
The Earth’s rotation seems constant, but in reality this speed undergoes numerous small fluctuations that go unnoticed by most of the planet’s 8 billion human inhabitants. Earthquakes, volcanoes, tidal forces and wind patterns can affect how fast or slow the world turns, and a recent study published in Nature hypothesizes that the redistribution of mass from the poles to the rest of the world’s oceans, i.e. the melting of polar ice, is slowing the planet’s rotation. Interestingly, this is actually delaying an unprecedented moment in history: the first ever elimination of a leap second. The slowdown is counteracting the acceleration.
Throughout Earth’s history, its rotation has continued to slow down. About 1.4 billion years ago, a day lasted 18 hours and 41 minutes, and during the age of dinosaurs a day lasted only 23 hours. This is a rather slow process, so slow that an Earth day lasts only 0.047 seconds longer than at the end of the Bronze Age. However, recently, Earth has bucked the trend due to the rotation of the planet’s liquid outer core, which is actually speeding up the process. Now, the study claims that climate change will likely delay the need to eliminate the leap second to 2028 or 2029.
“Even a few years ago, the expectation was that leap seconds would always be positive, and would occur more and more often,” explained study author Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at UC San Diego. “However, if you look at the changes in the rotation of the Earth, which is the reason for the leap seconds, and analyze the causes of these changes, it seems that a negative change is very likely to occur. One second doesn’t seem like a lot, but in today’s interconnected world, the wrong time could lead to huge problems“.
According to Scientific Americanit is likely that scientists would have had to eliminate the leap second much earlier if climate change had not occurred, but warming polar ice caps have delayed the need to make this unprecedented decision: delayed, but not avoided.
“There has never been a negative leap second before, and leap seconds themselves have always been a problem for people who run computer networks,” Agnew told Scientific American. Since many critical systems rely on precise time, “having to include a negative leap second would be a bigger problem because they’ve never had to do that“.
The Earth’s rate of rotation is slowing down in the long term
Scientists know that the Earth’s rate of rotation is, in the long term, slowing. This is due to celestial mechanics. A day on Earth lasts 24 hours, largely due to the tidal forces of the Moon. Essentially, the Moon takes rotational energy from the Earth to put it in an orbit farther from the Earth. This means that the Earth rotated faster in the past, with days lasting a fraction of what they do now. In about 200 million years, the length of a day on Earth is expected to reach 25 hours.
However, it is not a constant drift. A recent study in tidal flat muds preserved in sedimentary rocks suggests that about 1 to 2 billion years ago, the length of a day was stuck at 19 hours for about a billion years. The authors argue that this was mainly due to stronger solar atmospheric tides and not the gravitational effect of the Moon. It was during this period of relative calm that the largest increases ever recorded in oxygen levels on Earth appear to have occurred.
The acceleration of the Earth
Time on Earth is based on Coordinated Universal Time (Coordinated Universal Time – UTC), which strictly follows the rotation. Since the Earth’s rotation rate changes, seconds can be added or subtracted as needed. So far, only “leap seconds” have been added. For example, the IERS added a Leap Second on December 31, 2016.
In recent years, however, the Earth has become faster. After a long series of years in which the average day became slightly longer, 2020 recorded the 28 shortest days since 1960, when atomic clocks began making measurements. This acceleration continued until 2010, and on July 29, 2022, atomic clocks recorded a day lasting 1.59 milliseconds less than 24 hours.
Howeverthe average day lengthened by -0.08 milliseconds in 2023 and is now set to lengthen even further in 2024.
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