Climate melting is slowing the Earth's rotation

The melting of ice caused by climate change is affecting the rotation of the Earth.

The redistribution of the now liquid frozen masses would be slowing the planet's spin on its axis as if it were a skater extending his arms.

The phenomenon, which joins others that is affecting the Earth's movement, such as the slowdown in the core, will have its impact on time, increasing the lack of synchrony between universal and atomic time.

Mathematics says that a day has 86,400 seconds, but they are wrong.

Days on Earth do not have that exact length because the Earth's rotation is not regular.

Among the factors that intervene in this irregularity are the friction of the tides or the fact that the planet is not a solid sphere, but is made up of different solid or liquid masses, both on its surface and inside.

Despite such irregularity, the astronomical second was accepted as the basis of universal time (UT1).

But in 1967, the internationally accepted definition of the second changed.

The measurement of time, which had been linked to the Earth's rotation, became determined by the first atomic clocks, the basis of Coordinated Universal Time (UTC).

But its precision is such that the lack of synchrony between universal time and UTC had to be recovered by introducing a leap second every so often.

Now a new problem appears, the need to subtract a second instead of adding it, a problem that has to do with climate melting.

The connection has been established by the researcher at the University of California in San Diego (United States) Duncan Agnew.

For years, Agnew has studied the so-called postglacial rebound.

For more than 100,000 years, much of the northern hemisphere was covered in ice.

But it was not a thin layer.

As in Antarctica today, it was a layer two or three kilometers high.

With the end of the last ice age, about 11,000 years ago, the Earth's crust, freed from so much weight, rose, thereby disrupting the rotation of the planet.

This has caused the days to become longer.

To this isostatic adjustment, Agnew now adds the accelerated melting that is occurring in continental frozen masses, such as those in Greenland, due to climate change.

“The meltwater goes to the ocean and raises sea level.

This is equivalent to a transfer of mass from the poles to the equator, which slows down the speed of the Earth's rotation,” Agnew says in a note.

As he details in a work published in the scientific journal

Nature

, until 1990, measurements of the planet's gravity showed that it was spinning faster.

But his measurements based on satellite records find that this trend has reversed and has caused the Earth to spin more slowly.

The researcher at the High Energy Physics Laboratory of the Federal Polytechnic School of Lausanne (Switzerland) María Vieites, not related to this research, compares what Agnew observed with figure skating: “The ice that concentrates at the poles works as the skater's arms.

Upstairs, they are very close to the axis and that makes turning easier, but when you lower them and extend them, it slows down.”

Like the extremities, meltwater spreads across the planet in a redistribution of mass that affects rotation.

The slowdown of the earth's core

Agnew also introduces another factor into his equation.

In addition to tidal friction and melting ice, the irregularity of the Earth's rotation also involves the behavior of the planet's core, which is also liquid.

In January 2023, it was found that the Earth's core was slowing down, even turning in the opposite direction to the rest of the planet.

The slowdown is going to affect the weather.

“Extrapolation of the causes of the change in the speed of the Earth's rotation suggests that, by 2029, the time scale generally used will require, according to current rules, that a minute lasts only 59 seconds,” says the American geophysicist.

“This has never happened before and poses a huge challenge to ensuring that all parts of the global timing infrastructure show the same time,” he adds.

Currently, Coordinated Universal Time is calculated thanks to some 450 atomic clocks spread throughout the planet.

Its signal is broadcast in real time by about 80 time laboratories.

They are the temporal basis of the internet, financial systems, satellites... Since 1972, irregularities in the movement of the Earth have forced 27 leap seconds to be added, at irregular intervals and with a maximum of only six months in advance each time.

What this work shows is that now they will have to face the opposite, subtracting a second.

“The negative leap second has never been implemented,” recalls Commander Héctor Esteban Pinillos, head of the Time Section of the Royal Institute and Observatory of the Navy (ROA), the body in charge of setting the official time in Spain.

“We don't know how it will affect different systems, especially older ones,” he adds.

The fact that leap seconds have always been positive could have led to “the programmers not having taken the negative second into account in the code,” he adds.

But the captain believes that, in due course, “the impact will be economic, but the internet will not go down.”

However, they will have the problem in a few decades.

Since the 70s of the last century, leap seconds were added to the last minute of the year or the first minute of the next, although there were large companies like Amazon or Google that distributed them over the previous or following 24 hours.

But the International Bureau of Weights and Measures (BIPM, for its acronym in French), world coordinator of metrology, is studying retiring this adjustment method.

The logic so far is explained by María Dolores del Campo, director of the division of mechanical magnitudes and engineering of the Spanish Metrology Center: “so that the UTC was in accordance with the time scale calculated through the rotation of the earth (UT1 ) a second was added every time the difference between the two approached 0.9 s.

If the difference were negative, due to the change in the speed of rotation of the earth, a second would have to be removed.”

But it will not be necessary because, as Del Campo says, “at the 2022 General Conference on Weights and Measures it was approved to stop introducing leap seconds (neither positive nor negative) until the year 2035, since it is a problem in all systems. of communication and positioning to have to introduce this correction.”

What is going to be done from that year onwards has yet to be decided, but Del Campo points out that the idea most likely to become the norm is “not to reintroduce leap seconds until the difference between UTC and UT1 is greater than, for example, one minute;

which may lead to not having to introduce them until perhaps more than a century.”

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