Climate change will soon make Earth’s days longer. Here’s what that means for the planet

The effects of climate change are pervasive, from biodiversity loss to extreme weather events, rising sea levels, wildfires and human mass migration. With each year that passes, we learn more about our impact on the environment – some of which are more surprising than others.

Joining the list is one of the most seismic findings to date: scientists have recently discovered that our greenhouse gas emissions are changing how Earth spins.

The consequence? Earth’s days are getting longer, which could dramatically affect how we keep time in the coming years.

“It’s fascinating that we, as humans, with the record change in the climate we’ve caused over the past 100 years, can impact the whole Earth like that,” says Prof Benedikt Soja, a scientist at ETH Zürich who helped uncover the troubling trend.

“This could be larger than any previously dominant effect on our planet’s rotation.”

More hours in the day?

We’re all familiar with the greenhouse effect: as we emit gases such as carbon dioxide, Earth’s atmosphere traps more heat, causing global temperatures to rise.

Last year, the temperature around the world was 1.18°C above the 20th-century average, bringing us closer to the 1.5°C limit set in 2015 as the upper-bound target for avoiding the worst effects of climate change.

A major consequence of this warming is the melting of vast ice regions at the North and South Poles. Switzerland has lost 10 per cent of its glacial mass in the past two years. Antarctica loses 150 billion tonnes of ice annually, while Greenland loses 270 billion tonnes.

While many are (rightfully) concerned about how this melting affects coastal regions, Soja and his team asked a different question: how does this huge redistribution of mass affect Earth on a larger scale? And in a recent study published in the journal Proceedings of the National Academy of Sciences of the USA (PNAS), they answered that question.

“As the ice melts, Earth’s mass is being redistributed from the polar regions to the oceans,” Soja says. “This means that Earth has become more oblate, flattened even, with mass further away from the axis of rotation.”

Understanding the mechanics

Earth, like any rotating body, obeys the law of conservation of momentum, which can be briefly explained like this: momentum must be conserved; momentum depends on the moment of inertia and the speed of rotation; if mass moves further from the axis of rotation, the moment of inertia increases.

As such, to maintain momentum as the ice melts, Earth’s rotation slows down, making our days longer.

This concept, Soja explains, is similar to a figure skater performing a spin. When spinning with their arms outstretched, their spin slows, but when they pull their arms in it speeds up.

The effect that altering the distance between mass and the axis of rotation can have is seen when a figure skater uses their arms to change the speed of their spin

The study found that from 1900 to 2000, the climate’s effect on the length of Earth’s day hovered between 0.3 and 1.0 milliseconds per century. Since 2000, accelerated melting has increased this rate to 1.3 milliseconds per century. In a worst-case scenario, this could rise to 2.6 milliseconds per century by 2100 if emissions remain unchecked.

Clearly, these are small changes, imperceptible to us as we go about our daily lives. For our precisely synchronised global network of technology, however, the effects could be monumental.

It’s all in the timing

Depending on the timescale you use to examine Earth’s rotation, different effects play a dominant role.

Over many thousands of years, our days are perpetually doomed to get longer due to tidal friction caused by the Moon. Around 1.4 billion years ago a day was just 19 hours long – it’s been steadily getting longer ever since.

But other factors are at play too. For example, since the last Ice Age, land that was once pressed down by vast ice sheets has been slowly rebounding. This has the effect of moving Earth’s mass further north, closer to the axis of rotation, and, in the process, shortening the length of the planet’s days.

“Earth’s crust doesn’t spring back into place immediately [after it’s been pushed down], but oozes back to equilibrium over a period of time,” says Duncan Agnew, an emeritus professor at the Scripps Institution of Oceanography.

“That means that mass is effectively moving from south to north because the areas in the north are rising,” he says.

To complicate matters further, over a scale of decades, another force rumbling away beneath our feet has a dominant effect – Earth’s core.

Earth’s core rotates independently of the surface, speeding up and slowing down on an unpredictable (and at present, poorly understood) cycle.

Agnew explains that, since the 1970s, Earth’s core has been slowing down, which, due to the conservation of momentum, means the surface must speed up to make sure the whole system stays in balance.

In short, the length of our days is a push and pull between all these factors. Over a few decades, Earth’s core may speed up or slow down, forcing the opposite effect upon the surface. Yet, over hundreds of years, these swings of pace in the core average out to have no major effect on Earth’s rotation.

Tidal friction from the Moon is constantly trying to apply Earth’s brakes – Credit: Getty Images
The only lasting, dominant effect is the tidal friction from the Moon, which is forever trying to grind us to a halt, just very, very slowly.

But human-induced climate change is throwing this balance off kilter. Earth’s rotation is being slowed down faster than we expected. The consequences could be massive, though not necessarily negative.

The trouble with timekeeping

When it comes to timekeeping, three main timescales play crucial roles: International Atomic Time (TAI), Universal Time (UT1) and Coordinated Universal Time (UTC). TAI is based on atomic clocks, UT1 is determined by Earth’s rotation and UTC is the generally used timescale that attempts to reconcile the two.

Leap seconds were introduced in 1972 to keep UTC aligned with UT1, to within 0.9 seconds.

Unlike leap years, which are predictable, leap seconds are added irregularly as needed. Since 1972, 27 leap seconds have been added, the most recent being in 2016. We added nine leap seconds in the 1980s alone, but only three in the 2010s and, so far, none in the 2020s.

This ad hoc system causes serious problems in our interconnected digital age – particularly for the tech companies tasked with keeping everything in sync.

Notably, in 2012, a leap second caused disruptions for the likes of Reddit, Instagram, Pinterest, LinkedIn and Netflix. More than 400 Qantas flights were also delayed when the airline’s booking and check-in system was struck by the additional second.

The recent revelation that Earth’s core is slowing has complicated matters further. If the planet’s rotation continues to speed up, a negative leap second – removing a second from UTC – may become necessary. This unprecedented situation poses even greater challenges, as many systems aren’t designed to handle a negative adjustment.

“This has never happened before. And truthfully, I don’t think anybody really ever thought it would,” Agnew says. He likens the scenario to ‘Y2K’, when fears of potential computer errors spread at the turn of the century.

“The key thing is that we don’t know what might happen if we implement a negative leap second,” he warns. “It’s likely that the bad things that’ll happen are the ones we haven’t thought about.”

According to Agnew’s calculations, a negative leap second would have been needed in 2026 if it weren’t for the slowing effects of climate change. “Global warming has postponed the negative leap second and may negate the need for it all together,” he says.

So, there you have it, we may have found the only positive effect of global warming. The more ice that humanity melts, the less likely it is that we’ll need a negative leap second as the dominant slowing effects take over once more.

It’s probably not something to celebrate, though, given the downsides of further greenhouse gas emissions. Anyway, as things stand, a negative leap second might still be needed in 2029.

Perhaps instead it’s time to rethink our systems?

Agnew suggests a solution: lowering the required precision between timescales. This would make negative leap seconds unnecessary and allow more predictable scheduling of positive adjustments.

“It might make it more like leap years, where you add a fixed amount of seconds at a fixed time and you would just say, ‘Well, this isn’t exactly right, but we can live with it’,” Agnew says.

This makes sense as over longer periods, the dominant slowing would be all that matters, rather than the complicated behaviour of Earth’s core or ice melting.

Planning towards deploying this method is supposedly underway, hopefully in time to eliminate the need for leap seconds by 2035. However, achieving international consensus presents a challenge. If no changes are made before a negative leap second is needed, the resulting chaos could be unprecedented. Time is running out – literally.