April 24, 2024

Why do we need a leap second? A physicist explains what is disrupting the Earth’s rotation

This article has been reviewed in accordance with Science X’s editorial process and policies. The editors have highlighted the following attributes, ensuring the credibility of the content:

checked

trusted source

review


The Earth’s rotation rate is constantly changing due to gravitational forces as well as climate change, says Jacqueline McCleary, associate professor of physics at Northeastern University. Credit: Matthew Modoono/Northeastern University

× to close


The Earth’s rotation rate is constantly changing due to gravitational forces as well as climate change, says Jacqueline McCleary, associate professor of physics at Northeastern University. Credit: Matthew Modoono/Northeastern University

Meltwater from the polar ice caps, combined with the changing rotation of the Earth’s core, is disrupting the Earth’s rotation to such an extent that we may need to adjust for a “negative leap second.”

The effects of climate change can be seen everywhere, in the global refugee crisis, in an even worse allergy season, and now even in the concept of time itself.

Scientists have recently identified how meltwater from the polar ice caps is throwing off Earth’s rotation to such an extent that those who really care about accurate timing may have to implement a “negative leap second.”

Does this mean our days will suddenly be 25 hours long? No, but even a one-second change is significant in a world built on digital systems, like GPS, that rely on precise timing to function correctly.

“For as long as there has been an organized society, we have been trying to control time, or at least the days or seasons,” says Jacqueline McCleary, assistant professor of physics at Northeastern University. “The core, the crust, the oceans, climate change, glacial isostatic adjustment –– all these factors [are] contributing to a change in the Earth’s rotation rate at a measurable pace, something that would accumulate to a second per year or so.”

There are two main timing methods. Coordinated Universal Time (UTC), also known as astronomical time because it is based on the Earth’s rotation and position among the stars, has long been used as a global standard for clocks and timekeeping. This is what time zones and what most people call “time” are based on.

However, Earth’s rotation isn’t exactly a constant beat, says McCleary. In fact, it is always changing as the gravitational forces of the Sun, Moon and Earth, as well as the Earth’s tides and even the rotation of its core, act on each other.

To account for this, timekeepers—who demanded a more exact standard—began using atomic time, or International Atomic Time, to arrive at the exact speed at which our clocks run. This measurement varies so little that it could very well be static.

In 1958, the international timekeeping community agreed to synchronize UTC and TAI.

However, in 1972, scientists noticed that the Earth’s rotation was starting to slow slightly, making the days a little longer. As a result, atomic and astronomical time began to diverge slowly but steadily. To keep them in sync – a growing need as more and more digital systems, such as GPS satellites, require even more exact levels of precision – the “leap second” was created.


Although leap seconds are small adjustments to our time systems, they can have a big impact on systems like GPS. Credit: Alyssa Stone/Northeast University

× to close


Although leap seconds are small adjustments to our time systems, they can have a big impact on systems like GPS. Credit: Alyssa Stone/Northeast University

McCleary says there are several factors responsible for the decreasing rate of Earth’s rotation, including so-called tidal locking.

“The Moon pulls on the Earth, the Earth pulls on the Moon, and over time the effect of that is that the Earth slows down in a tiny way — like one part in 10 billion — but in a non-negligible way,” says McCleary.

Glacial melting that has occurred since the Ice Age and, more recently, melting of polar ice resulting from human-caused climate change have also contributed to the slowing of Earth’s rotation, McCleary says. In both cases, the meltwater disperses, creating a mass of water around the equator, while at the same time the land previously trapped under the ice at the poles emerges again.

These two forces together make it harder for the Earth to rotate, which means the UTC day is technically longer. This phenomenon has been observed for decades.

“As the glaciers melt and the Earth slowly returns and the mass that was once at the poles is redistributed towards the equators – because the liquid spreads more easily, the liquid responds to the rotation – the Earth’s rotation rate slows,” it says McCleary. .

However, more recently, scientists discovered that the Earth is no longer slowing down. In fact, it’s starting to accelerate a bit. Leap seconds were added almost every year between 1972 and 1999 to adjust for the slowing of Earth’s rotation. But only four have been added in the last 23 years, and the last time a leap second was added was in 2016.

What scientists have found is that while climate change is “pulling on the brakes,” says McCleary, the liquid part of Earth’s core is also slowing down, affecting the rotational speed of the planet’s surface.

“The core of the Earth, the liquid part, also spins, and sometimes it just experiences random changes, random fluctuations,” says McCleary. “Right now, the Earth’s core over the past few decades has slowed down randomly and through a complicated series of interactions between the liquid part of the core and the mantle and crust, or the solid part of the Earth, the crust is spinning faster. This random change in the rotation of the core, specifically a slowdown in the rate of rotation, translates into an acceleration of the rotation of the Earth’s surface, which would have the effect of shortening the days.”

Within a few years, it could result in the implementation of a negative leap second to keep atomic and astronomical times synchronized, although the impacts of melting polar ice could ultimately delay our need to change clocks from 2026 to 2029.

Would adjusting the clocks by one second make that much of a difference? McCleary says this could impact global systems in a major way.

“While our computing infrastructure is equipped to handle positive leap seconds, essentially none of our networks or web services are equipped for negative leap seconds,” she says. “They don’t know how to go from 12:00:03 to 12:00:02. This is essentially on the same level as the Y2K bug, where you had to reprogram everything to allow for four-digit years.”

Similar to Y2K, McCleary says it probably wouldn’t end up causing a catastrophe. While this could impact the precision timekeeping community and atomic time, McCleary says the alternative to letting “a few seconds float away” is to “reprogram the Internet.” In this case, a little wasted time might not be a bad thing.

Leave a Reply

Your email address will not be published. Required fields are marked *