Length of days on Earth is increasing at ‘unprecedented’ rate
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If it feels like the days are dragging on more than usual lately, scientists say that you might not be alone.
Researchers from ETH Zurich have revealed that climate change is causing the length of days on Earth to increase at an ‘unprecedented’ rate.
As polar ice melts in Greenland and Antarctica, the Earth’s centre of gravity shifts towards the equator, gradually slowing down the planet’s rotation.
If emission levels are not reduced, the researchers predict that this shift could add 2.62 milliseconds to the day by the end of 2100 – a greater impact than that of the moon.
While the effects won’t noticeable to most humans, the researchers say that the subtle changes could wreak havoc for space travel.
Scientists have revealed that the Earth’s days are getting longer at an ‘unprecedented rate’ due to climate change
While it might seem odd that humans could have an effect on something as inevitable as the passage of the day, the physics is actually quite simple.
As human-caused climate change causes global ocean temperatures to rise, melting water flows away from the polar ice caps towards the equator.
Co-lead author Benedikt Soja, of ETH Zurich, explains: ‘It’s like when a figure skater does a pirouette, first holding her arms close to her body and then stretching them out.
‘The initially fast rotation becomes slower because the masses move away from the axis of rotation, increasing physical inertia.’
As the Earth’s rotation is slowed, the time it takes to rotate on its axis increases and the days become subtly longer than the 86,400-second standard.
This is not the only thing that can cause changes in the Earth’s rotation since the speed of the planet is also affected by the pull of the moon and conditions in the inner layers.
As polar sea ice from the Antarctic (pictured) and Greenland melts, the freshwater travels to the equator where it shifts the balance of the Earth, slowing the planet’s rotation
However, in two recent papers, the researchers have now managed to separate the different impacts of each of these factors.
For most of the Earth’s history, the biggest drag on the day’s length has been ‘tidal friction’ caused by the Moon’s gravity pulling on the ocean.
Tidal friction has added about 2.4 milliseconds to the length of the day every century over millions of years.
From 1990 till today, the researchers estimate that the shift in water due to climate change has added 0.8 milliseconds to the day.
However, in a high emissions scenario in which greenhouse gas emissions are not reduced, the researchers predict that the rate of change could double by 2100.
While humans might not feel the effects, space missions like NASA’s Ingenuity probe (pictured) could miss their targets as the planet’s rotation changes
By the end of the century, climate change could add more than 2.62 milliseconds per century – making it the single biggest factor in changing the length of the day.
These effects will be so subtle that humans will not be able to notice the change over a single lifetime, however, the researchers warn that this could still have a major impact on space travel.
Dr Soja says: ‘Even if the Earth’s rotation is changing only slowly, this effect has to be taken into account when navigating in space—for example, when sending a space probe to land on another planet.’
Across the vast distances of space covered by planetary probes such as NASA’s Perseverance and Ingenuity, a deviation of just one centimetre on Earth could mean missing the target by hundreds of metres.
This is especially key for precision landings aiming to touch down at very specific points on distant planets.
Scientists will need to accurately estimate the exact course of Earth’s rotation for future space missions.
As the Earth’s liquid metal outer core shifts, this causes the Earth to slightly wobble on its axis in an effect known as Polar motion
The researchers used precise measurements to separate the effects of core dynamics from the effects of changes to the Earth’s surface on the planet’s Polar motion
The researchers believe that climate change could be affecting the conditions in the Earth’s inner core, triggering the shift in the rotational axis illustrated by the blue line in this graph
Dr Soja adds: ‘Otherwise, it won’t be possible to land in a specific crater on Mars.’
In addition to changing the speed of Earth’s rotation, the researchers also discovered that climate change might be tilting the planet on its axis.
The scientists used a technique called Very Long Baseline Interferometry which measures how long it takes radio signals to reach Earth from space.
This allowed them to take very accurate measurements of the Earth’s ‘polar motion’, the change in axis of spin relative to the Earth’s surface.
They discovered that changes in polar motion are jointly affected by a combination of changes on the surface and shifts deep within the Earth’s liquid metal outer core.
As mass shifts within the Earth under the intense pressure of the outer layers, this slightly tilts the planet on its axis.
Shifts in water at the surface have a similar effect, but the researchers also made the surprising discovery that climate change could be affecting conditions deep within Earth.
Dr Soja says: ‘Climate change is causing the Earth’s axis of rotation to move, and it appears that the feedback from the conservation of angular momentum is also changing the dynamics of the Earth’s core.’
Their researchers uncovered that this feedback effect could lead to changes in the Earth’s tilt over time.
However, these are unlikely to have any serious or noticeable effects on the surface.
Co-lead author Dr Diani Shahvandi of ETH Zurich adds: ‘Ongoing climate change could therefore even be affecting processes deep inside the Earth and have a greater reach than previously assumed.’
