Struggling to wrap your head around daylight savings time this weekend? Spare a thought for the world's timekeepers, who are trying to work out how climate change is affecting the Earth's rotation – and in turn, how we keep track of time.
The Earth’s speeding rotation is threatening to mess with time, clocks and computers in an unprecedented way.
For the first time in history, world timekeepers may have to consider resetting our clocks because the planet is rotating faster than it used to.
Yet a new study suggests that climate change is slowing it down – pushing back the point at which the world's atomic clocks will have to skip back for what scientists call a “negative leap second”.
Out of sync
Throughout history, time has been measured by the rotation of the Earth.
However, in 1967, scientists embraced atomic clocks – which use the frequency of atoms as their tick-tock – ushering in a more precise era of timekeeping.
Nonetheless timekeeping has remained aligned with the Earth's rotation for historical and navigational reasons.
But our planet is an unreliable clock, and has long been rotating slightly slower than atomic time – meaning the two measurements were out of sync.
So a compromise was struck. Whenever the difference between the two measurements approached 0.9 of a second, a "leap second" was added to Coordinated Universal Time (UTC) – the internationally agreed standard by which the world sets its clocks.
Though most people likely have not noticed, 27 leap seconds have been added to UTC since 1972, the last one coming in 2016.
But in recent years a new problem has emerged that few saw coming: Earth's rotation has been speeding up, overtaking atomic time.
This means that to synchronise the two measurements, timekeepers may have to introduce the first ever negative leap second – a minute with only 59 seconds.
Nature research paper: A global timekeeping problem postponed by global warming https://t.co/5DU1v0VDy9
— nature (@Nature) March 28, 2024
Unpredictable planet
"This has never happened before, and poses a major challenge to making sure that all parts of the global timing infrastructure show the same time," according to Duncan Agnew, a researcher at the University of California, San Diego.
"Many computer programs for leap seconds assume they are all positive, so these would have to be rewritten," he told French news agency AFP.
Partly using satellite data, Agnew looked at the rate of the Earth's rotation for a new study published in the journal Nature.
Complex geophysical processes work to change the time the planet takes to rotate, which has gradually slowed over millennia. But in recent decades, its rotation rate has been accelerating.
Now the study suggests that starting from 1990, melting ice in Greenland and Antarctica has slowed down the Earth's rotation by redistributing mass from the poles to lower latitudes.
"When the ice melts, the water spreads out over the whole ocean; this increases the moment of inertia, which slows the Earth down," Agnew said.
This human-induced process has had the knock-on effect of reducing the gap between atomic and standard time, effectively delaying the need for a negative leap second until at least 2029.
"When the ice melts, the water spreads out over the whole ocean; this increases the moment of inertia, which slows the Earth down," Agnew said.
He determined that if not for climate change, a negative leap second might have needed to be added to UTC as soon as 2026.
Scrapping the leap second
Some experts fear that introducing a negative leap second into standard time could wreak havoc on computer systems across the world. Even positive leap seconds have previously caused problems for systems that require precise timekeeping.
That's partly why the world's timekeepers agreed in 2022 to scrap the leap second by 2035.
From that year, the plan is to allow the difference between atomic time and the Earth's rotation to grow up to a minute.
A subsequent leap minute to bring them into sync is not expected to be needed in the next century.
And "a negative leap minute is very, very unlikely", Agnew said.
He hopes his research will prompt the world's timekeepers to consider dropping the leap second sooner than 2035.
(with AFP)
