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Climate change is causing days to get longer by slowing down the Earth
The melting of the polar ice caps is affecting how fast our planet spins.
As the polar ice caps melt, the speed of the Earth’s rotation is being slowed down, making days slightly longer than they might otherwise be.
When it comes to climate change, it’s all a matter of time.
Rising temperatures are affecting many aspects of our planet through changing weather patterns, animal migrations and plant flowering to name but a few. A new study suggests that climate change is also having an unappreciated impact – it influences how we measure time.
As the polar ice caps melt, the resulting sea level rise is slowing down the Earth’s spin ever so slightly. While the extra fractions of a second may not affect us in our daily lives, their buildup could cause problems for navigation and communication technology where timing is everything.
Professor Duncan Agnew, from the Scripps Institution of Oceanography, is the author of a Nature paper describing this phenomenon.
“Imagine a skater spinning on the ice,” Duncan says. “If they hold their arms out, their spinning is slower, but if they bring them into their body, then they speed up. This demonstrates the conservation of angular momentum, a principle which applies to all spinning objects including the Earth.”
“As polar ice melts, the water spreads out over the whole ocean, causing the same effect as the skater spreading their arms out – the Earth slows down. More rapid melting would slow the Earth more rapidly, opposing the overall speedup of the planet that has been seen in recent years.”
Sea levels have risen at an unprecedented rate as rising temperatures cause ice to melt and seawater to expand. © Bernhard Staehli/ Shutterstock.
Why isn’t a day always the same length?
While we might think of the Earth as a globe, it’s not actually a perfect sphere. Instead, it’s more properly referred to as an oblate spheroid – a sphere that has been squashed from top to bottom, causing it to bulge out at the equator.
Our planet is also not quite as solid as we might think. The different layers of the Earth, from its core out to the atmosphere, all have their own properties that affect exactly how it spins. As a result, it can take fractionally more or less than 24 hours to complete a single rotation.
This variation is happening for many different reasons, from the rebound of continents to seismic activity. The Boxing Day earthquake of 2004, for example, made our planet bulge slightly less at the equator, speeding up its rotation by around three millionths of a second.
More significant impacts are caused by the Sun and Moon as their gravity warps the shape of the Earth. Their pull on the oceans also has an impact, causing a process known as tidal friction which decelerates the planet.
Over millions of years, this has generally caused the Earth’s spin to slow down. However, in the past few decades, our planet has been in a hurry. The shortest day in recorded history took place on 29 June 2022, when 1.59 milliseconds was shaved off 24 hours.
This is just one of a number of short days which have taken place in the past few decades. The Nature paper suggests that it is caused by the spin of our Earth’s core slowing down relative to the surface, meaning the rocky parts of the planet have to spin faster to conserve momentum.
While it’s not a difference we notice, it’s a growing issue for computers around the world.
Atomic clocks measure time much more precisely than those based on the Earth's spin. © geogif/ Shutterstock.
Time is relative
Until relatively recently, timing was tied directly to the rotation of the Earth. Scientists defined a second by dividing the time it took for the Earth to rotate by the number of seconds in a day, which is 86,400.
However, in the 1950s the development of atomic clocks meant that the second was redefined, based instead on the changing state of caesium atoms. Unlike the Earth’s rotation, these clocks are extremely stable, with the best losing just one second over 10 million years.
When international atomic time was originally introduced in 1958, it was linked to universal time to maintain a connection with Earth’s rotation. But maintaining this link has required 27 leap seconds to have been added over the years to bring both methods of timing back in line.
While we might not notice the leap seconds, they are a problem for systems which rely on time as there’s no easy way to add them in. The addition of a leap second in 2015 reportedly disrupted Twitter and the Android operating system, as well as crashing a number of internet networks.
But an even bigger problem is looming as the Earth speeds up. With the length of a day now shortening, a second will need to be deducted from universal time so it lines up with international atomic time.
This is an unprecedented issue. The Nature paper suggests that a negative leap second will probably be needed by 2029, something scientists and engineers did not see coming.
Climate change has put off this deadline by around three years as it slowed the Earth's speedup ever so slightly.
The result might be to actually fast-track plans currently being discussed to drop leap seconds altogether, which is currently proposed for 2035, and let atomic time and universal time slowly drift apart.
“I hope that this paper will at least cause people in timekeeping to consider dropping the leap second sooner,” Duncan says. “In any case, I think they should definitely change the rules to exclude negative leap seconds.”
“In the long run, tidal friction and melting ice will continue to slow the Earth down. Based on past data, the core is unlikely to keep speeding it up at a rate large enough to counteract this, so negative leap seconds will be rare anyway.”
While it’s by no means the most damaging aspect of climate change, the effect on our planet's spin show just how widespread our impacts on the Earth are.
