New research suggests climate change is turning Earth to its literal core.
As polar and glacial ice melts due to global warming, water that was once concentrated at the top and bottom of the globe is being redistributed towards the equator. The excess mass around the center of the Earth slows its rotation, which in turn has the effect of lengthening our days.
The new study offers further evidence of this dynamic, further suggesting that changes in planetary ice have been profound enough to affect Earth’s axis – the invisible line at its center around which it rotates. Together, these displacements cause feedback below the surface and affect the fluids that move in the Earth’s molten core.
The findings were published in two journals, Nature Geoscience and Proceedings of the National Academy of Sciences, over the past week.
The studies, along with similar research published in March, suggest that humans have tampered with fundamental elements of the planet’s physical properties — a process that will continue until global temperatures stabilize and the melting of ice sheets reaches equilibrium.
“You can add the rotation of the Earth to this list of things that humans have completely affected,” said the author of the two new studies, Benedikt Soja, an assistant professor of space geodesy at ETH Zurich in Switzerland.
The change in Earth’s rotation is significant enough that it could one day rival the effect of tidal forces caused by the moon, Soja said — if carbon emissions continue at extreme levels.
In general, the speed of Earth’s rotation depends on the shape of the planet and where its mass is distributed—factors governed by several opposing forces.
Scientists often offer the analogy of a figure skater spinning on ice: When skaters spin with their arms extended, their rotation will be slower. But if the skaters hands are held tight, they spin faster.
Somewhat similarly, the friction of ocean tides caused by the moon’s gravity slows Earth’s rotation. Historically, this has had the biggest effect on the planet’s rotation rate, Soja said.
Meanwhile, the slow rebound of the Earth’s crust in some high-latitude regions after the removal of Ice Age glaciers works in the opposite direction, speeding up the planet’s rotation.
Both of these processes have long been predictable influences on the Earth’s angular velocity.
But now the rapid melting of ice due to global warming is becoming a powerful new force. If humans continue to pollute the planet with carbon emissions, Soja said, the effect of ice loss could surpass that of the moon.
“So in worst-case scenarios, climate change would become the most dominant factor,” he said.
A fourth important factor influencing the rotation of the Earth is the movement of the fluid in its core. Scientists have long understood that this can speed up or slow down the rotation of the planet – this trend can shift in intervals of 10 to 20 years. Right now, the core is temporarily causing the Earth’s rotation to speed up slightly, counteracting the slowdown caused by climate change.
Climate change also appears to be affecting the Earth’s core due to melting ice and shifts in the planet’s rotation axis.
Scientists behind the new study created a 120-year model of polar motion, or how the axis shifts over time. They found that changes in the planet’s mass distribution due to melting ice likely contributed to small fluctuations in polar motion.
Soja estimated that climate change was most likely responsible for 1 meter of change per 10 years.
The research further suggests that the movement of molten rock inside the Earth adjusts to changes in its axis and rotation rate – a feedback process in which the Earth’s surface affects its interior.
“The spin is changing slightly, and that, we believe, can have an indirect effect on the core,” Soja said. “That’s something that’s not very easy or impossible to measure directly because we can’t go there.”
The findings have implications for how humans keep time and how we position satellites in space.
“For example, if you want to fly a new mission to Mars, we really need to know what the state of Earth is exactly in space, and if that changes, we could actually make a navigation error or a mistake,” Soja said.
For example, a 1-meter shift in Earth’s axis could mean that a spacecraft misses its target by 100 or 1,000 meters when it reaches Mars.
In terms of timekeeping, research published in March suggested that climate change has delayed the need to add a “negative leap second” to Coordinated Universal Time to keep the world clock in line with the Earth’s rotation.
Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego who led that earlier study, said the new research “fits in very well” with his work.
“It extends the result further into the future and looks at more than one climate scenario,” Agnew said, adding that although Soja and his co-authors took a different approach, they reached a result similar to his.
“Multiple discoveries are almost the rule in science — this is another case,” Agnew said.
Thomas Herring, a professor of geophysics at the Massachusetts Institute of Technology who was not involved in either study, said the new research may actually offer insight into how changes on Earth’s surface can affect what happens inside.
“In terms of feedback between surface processes and the core, I find that plausible,” Herring said in an email, explaining that “large-scale” processes at the surface can “penetrate the liquid core.”