New research shows that climate change is changing the Earth to its 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 toward the equator. The extra mass around the center of the Earth slows its rotation, which in turn has a longer effect on our days.
A new study provides more evidence of that dynamic, further suggesting that changes in the planet’s ice have been profound enough to affect Earth’s axis — the invisible line in its center around which it spins. Together, those shifts create feedback beneath the surface, affecting the fluids moving in Earth’s molten core.
The findings were published last week in two journals, Nature Geoscience and Proceedings of the National Academy of Sciences.
The studies, along with similar research published in March, show that humans have tampered with fundamental elements of the planet’s physical properties. This process will continue until global temperatures stabilize and the melting of the ice caps reaches equilibrium.
“You can add the Earth’s rotation to this list of things that humans have completely influenced,” said one of the authors of the two new studies, Benedikt Soja, an associate professor of space geodesy at ETH Zurich in Switzerland.
The change in Earth’s rotation is so large that it could one day rival the tidal forces of the moon, Soja said, if CO2 emissions remain at extreme levels.
In general, the speed at which the Earth rotates on its axis depends on the shape of the planet and the distribution of its mass. These factors are determined by various opposing forces.
Scientists often make an analogy to a figure skater spinning on ice: if skaters spin with their arms straight, their rotation will be slower. But if skaters keep their arms straight, they spin faster.
Similarly, the friction of ocean tides with the moon’s gravity slows Earth’s rotation. Historically, that has had the biggest impact on the planet’s rotation rate, Soja said.
Meanwhile, in some high-latitude areas, the slow recovery of the Earth’s crust after the disappearance of Ice Age glaciers is actually backfiring and accelerating the planet’s rotation.
Both processes have long had a predictable influence 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 impact of ice loss could exceed that of the moon.
“In the worst case, climate change would indeed become the most dominant factor,” he said.
A fourth major factor affecting Earth’s rotation is the movement of fluid in its core. Scientists have long understood that this can speed up or slow down the planet’s rotation — a trend that can shift over 10- to 20-year intervals. Right now, the core is temporarily causing Earth’s rotation to speed up a bit, 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 rotational axis.
The researchers behind the new study built a 120-year model of polar motion, or how the axis shifts over time. They found that changes in the distribution of mass on the planet due to melting ice likely contributed to the small fluctuations in polar motion.
Soja estimated that climate change was likely responsible for a change of 1 meter over a 10-year period.
The research also shows that the movement of molten rock within the Earth adapts to changes in the axis and rotational speed of the Earth. This is a feedback process in which the Earth’s surface influences the Earth’s interior.
“The rotation changes slightly and that could, we think, have an indirect effect on the core,” Soja said. “This is something that is not so easy or not so direct to measure because we can’t go down there.”
The findings have implications for how people keep track of time and how we position satellites in space.
“For example, if you want to do a new mission to Mars, we really need to know what the state of the Earth in space is, and if that changes, we can actually make a navigational error or a mistake,” Soja said.
For example, a 1-meter change in the Earth’s axis could cause a spacecraft to miss its target by 100 or 1,000 meters when it reaches Mars.
As for 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’s clocks 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 the earlier research, said the new research “fits in very nicely” 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 arrived at 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 could indeed provide insight into how changes on Earth’s surface can affect what happens inside.
“For the feedback between surface processes and the core, I find that plausible,” Herring said in an email, explaining that “large-scale” processes at the surface “could penetrate into the liquid core.”