Climate change and the melting of polar ice may affect the length of the day on Earth

By | March 28, 2024

A crack in an ice sheet and an ice sheet in Antarctica caused by climate change.

Humanity is quickly waking up to the fact that time is running out to take action to mitigate the effects of climate change. Ironically, climate change itself, caused mainly by the release of greenhouse gases through the burning of fossil fuels, could help delay a time-related crisis.

We currently keep official time using approximately 450 ultra-accurate atomic clocks to maintain Coordinated Universal Time (UTC), which was first defined in 1969. A more traditional historical method of timekeeping uses the Earth’s rotation . But because Earth’s rotation has fluctuated since 1972, the alignment between these two measurements has been maintained by adding 27 “leap seconds” to the official time standard.

However, new research led by University of California geologist Duncan Agnew suggests that the melting of ice in Greenland and Antarctica due to global warming could have an impact on Earth’s angular velocity, the speed at which the planet moves. rotates, and thus could lengthen the day, albeit by an amount as great as the speed at which the planet rotates. small, it is unnoticeable to humans, but not to computers that rely on accurate timekeeping.

“Global warming is already impacting global timekeeping,” Agnew and colleagues write in a paper published Wednesday (March 27) in Nature.

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Ice melting causes Earth’s angular velocity to decrease faster than before, which could require a “negative leap second” or eliminate a leap second, which is thought to be three years later than scientists expected.

The problem with this is that activities like network computing and financial markets require the consistent, standardized, and accurate timescale that UTC provides, and the addition of a negative leap second has never been tested before.

“A negative leap second has never been added or tested, so the problems it could cause are without precedent,” Patrizia Tavella, meteorologist at the Time Department of the Bureau International des Poids et Mesures (BIPM), wrote about the recent study in a accompanying News & Views paper. “Agnew’s suggestion that the change could be delayed is welcome news indeed.”

Tavella thinks that reducing the need for a negative leap second from 2026 to 2029 could help meteorologists better calculate Earth’s rotation. This improved information would help better assess whether a negative leap second is really necessary, while assessing the associated risks.

Earth is a poor timekeeper

The planet’s rotation rate has always fluctuated, but before the implementation of accurate timekeeping and technology, the only detrimental effect this had was to change the timing of eclipses and other astronomical events compared to records created by ancient astronomers and recorded.

“On a thousand-year time scale, changes in Earth’s rotation reflect the combined effect of three geophysical processes,” wrote Jerry Mitrovica of Harvard’s Department of Earth and Planetary Sciences in the News & Views Nature piece.

Mitrovica said one of these elements is the link between Earth’s iron core and the outer rocky mantle and crust. This means that any change in the angular momentum of the core must be compensated by an equal but opposite change in the mantle and crust. So as the core slows down, to keep Earth’s rotation consistent, the outer parts of the planet must accelerate at the same rate. However, both the core and upper layers have lost angular momentum.

In the past, this core-shell coupling has led to an increase in the Earth’s rotation period by 6 millionths of a second per year. While this speed slowdown may seem trivially small, it is actually felt by atomic clocks.

a cross-section of the Earth showing the different layers that make up the planeta cross-section of the Earth showing the different layers that make up the planet

a cross-section of the Earth showing the different layers that make up the planet

Agnew and colleagues turned to satellite gravity data to determine the decrease in Earth’s angular momentum and its effect on timekeeping.

It showed that increased melting of the Greenland and Antarctic ice caps has changed the mass distribution of our planet’s surface and more rapidly reduced the angular velocity of Earth’s solid outer layers, while the angular velocity of the largely liquid core continues to decrease consistently.

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“His analysis convincingly shows that core-mantle coupling has led to accelerated rotation, but that there has also been a pronounced slowdown due to the onset of the major melting of the polar ice caps that began towards the end of the twentieth century” , wrote Mitrovica. “This human-induced process slows rotation by moving melted ice mass from the poles to lower latitudes.”

Agnew and colleagues suggest that while UTC won’t need a negative leap second until 2029, the problem this change poses for the timing of computer networks will require changes in the way UTC is aligned with Earth’s rotation to be implemented sooner than later. currently planned.

“Unless international timekeeping guidelines change rapidly, the myriad technological foundations of human society will need to be updated in preparation for this unprecedented event and for the disappearance of 23:59:59 on a single day in the not-too-distant future,” Mitrovica concluded . .

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