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Melting ice caps are changing Earth's rotation, causing the need for a 'negative leap second'

As the world grapples with the far-reaching consequences of climate change, from the global refugee crisis to worsening allergy seasons, a new twist has emerged: the potential need for a “negative leap second” to keep our clocks in sync with the planet’s changing rotation.

Scientists have unraveled the intricate dance between Earth’s melting polar ice caps and the shifting spin of its core, revealing a startling impact on the very fabric of time itself.

Jacqueline McCleary, assistant professor of physics at Northeastern University, sheds light on this fascinating phenomenon.

“For almost as long as there’s been organized society, we’ve been trying to keep track of time, or at least days or seasons,” McCleary explains.

“The core, the crust, oceans, climate change, glacial isostatic adjustment — all of these factors [are] contributing to a change in the Earth’s rate of rotation at a measurable pace, something that would accumulate a second per year or something like that,” she continued.

Universal coordinated time vs. International atomic time

To understand the significance of this discovery, it’s essential to delve into the two primary methods of timekeeping: Universal Coordinated Time (UTC) and International Atomic Time (TAI).

UTC, also known as astronomical time, has long been the global standard for clocks and timekeeping, based on Earth’s rotation and position among the stars.

However, as McCleary points out, Earth’s rotation is far from a steady drumbeat, constantly influenced by the gravitational forces of the sun, moon, and Earth itself, as well as tides and the rotation of its core.

Enter atomic time, or TAI, a far more exacting standard that varies so little it might as well be static. In 1958, the international timekeeping community agreed to synchronize both UTC and TAI.

But by 1972, scientists noticed that Earth’s rotation was beginning to slow down ever so slightly, causing the two timekeeping methods to diverge. To keep them in sync, the “leap second” was born.

Glacial melt and polar ice melt

McCleary identifies several factors responsible for the declining pace of Earth’s rotation, including tidal locking.

“The moon pulls on Earth, Earth pulls on the moon and over time the effect of that is for the Earth to slow down in a minuscule — like one part in 10 billion — but non negligible way,” she said.

Glacial melt since the Ice Age and, more recently, polar ice melt stemming from human made climate change have also played a role.

As meltwater disperses, creating a mass of water around the equator, the land previously trapped under ice at the poles springs back up, making it more difficult for the Earth to rotate and lengthening the UTC day.

“As the glaciers melt and as Earth slowly springs back and as mass that was once at the poles gets redistributed to the equators — because liquid spreads more easily, liquid responds to being spun — the rotation rate of the Earth slows down,” McCleary elaborates.

Earth’s core is a hidden player in the timekeeping game

However, recent findings have revealed a surprising twist: Earth is not slowing down anymore. In fact, it’s starting to speed up ever so slightly.

While leap seconds were added almost every year between 1972 and 1999 to adjust for Earth’s slowing rotation, only four have been added in the last 23 years, with the last one in 2016.

Scientists have discovered that while climate change is “applying the brakes,” as McCleary puts it, the liquid part of Earth’s core is also slowing down, affecting the speed of the planet’s surface spin.

“The core of the Earth, the liquid part, rotates too, and it sometimes just experiences random changes, random fluctuations. Right now, the core of the Earth in the last few decades has randomly slowed down and by a complicated series of interactions between the liquid part of the core and the mantle and the crust, or the solid part of the Earth, the crust is spinning faster,” McCleary explains.

“This random change in the core’s rotation, specifically a slowing down in the rate of rotation, translates into a speeding up of the Earth’s surface rotating, which would have the effect of shortening days,” she noted.

Negative leap second: A timely adjustment

In a few years, this could result in the implementation of a negative leap second to keep atomic and astronomical time in sync, although the impacts of polar ice melt could end up delaying the need to shift the clocks from 2026 to 2029.

While adjusting the clocks by a second may seem insignificant, McCleary emphasizes the potential impact on global systems.

“Although our computer infrastructure is equipped to handle positive leap seconds, essentially none of our networks or web services are equipped for negative leap seconds,” McCleary warns.

“They don’t know how to go from 12:00:03 to 12:00:02. This is essentially on par with the Y2K bug where you had to reprogram everything to allow for four-digit years,” she concluded.

Much like the Y2K bug, McCleary believes that a negative leap second likely wouldn’t cause catastrophe. However, it could impact the precision timekeeping community and atomic time.

In the end, she suggests that the alternative to letting “a couple of seconds float” is “reprogramming the internet,” and in that case, a little lost time might not be such a bad thing after all.

Melting ice, shifting time, and negative leap seconds

In summary, as we navigate the complexities of a changing planet, we must recognize the intricate dance between Earth’s melting ice caps, shifting core, and the very concept of time.

The potential need for a negative leap second serves as a stark reminder of the far-reaching impacts of climate change and underscores the importance of understanding the delicate balance that governs our world.

While adjusting our clocks by a mere second may seem trivial, it represents a significant challenge for the precision timekeeping community and the global systems that rely on accurate time.

As we move forward, we must embrace the chaos and find innovative solutions to adapt to the shifting sands of time, ensuring that our technological infrastructure keeps pace with the ever-changing rhythms of our planet.

The full study was published in the journal Nature.


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