Climate change is altering the Earth to its literal core, new research shows.
As polar and glacial ice melts due to global warming, water that was once concentrated at the top and bottom of the globe is redistributed towards the equator. The extra mass around the center of the Earth slows its rotation, which in turn has the effect of lengthening our days.
A new study offers more evidence of this dynamic and further suggests that changes in the planet’s ice have been profound enough to affect Earth’s axis – the invisible line at its center around which it spins. Together, these changes cause feedback below the surface, affecting 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, in 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 melting ice sheets reach equilibrium.
“You can add the rotation of the Earth to that list of things that humans have completely influenced,” said the author of the two new studies, Benedict Soya, assistant professor of space geodesy at ETH Zurich in Switzerland.
The change in Earth’s rotation is significant enough to one day rival the effects of tidal forces caused by the moon, Soya said — if carbon emissions continue at extreme levels.
In general, the speed of the Earth’s rotation depends on the shape of the planet and on where its mass is distributed – factors governed by several opposing forces.
Scientists often offer a comparison to a figure skater spinning on ice: when skaters spin with their arms outstretched, their spin will be slower. But if skaters’ arms are tight, they spin faster.
Similarly, the friction of ocean tides from the Moon’s gravitational pull slows Earth’s rotation. Historically, this has had the biggest impact on the planet’s spin rate, Soya said.
Meanwhile, the slow rebound of Earth’s crust in some high-latitude regions after the Ice Age deglaciations worked in the opposite direction, speeding up the planet’s rotation.
Both processes have long been predictable influences on 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, Soya said, the impact of ice loss could surpass that of the moon.
“In the worst case scenario, then yes, climate change will become the most dominant factor,” he said.
A fourth important factor influencing the rotation of the Earth is the movement of the liquid in its core. Scientists have long understood that this can speed up or slow down the planet’s rotation, a trend that can shift in 10- to 20-year intervals. Right now, the core is temporarily causing the Earth’s rotation to speed up slightly, counteracting the slowdown due to climate change.
Climate change also appears to be affecting the Earth’s core as a result of melting ice and shifting the planet’s axis of rotation.
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 planet’s mass distribution due to melting ice likely contributed to small fluctuations in polar motion.
Soya calculated that climate change is most likely responsible for 1 meter of change in 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 rotation changes slightly, and that, we think, may indirectly have an effect on the core,” Soya said. “It’s something that’s not very easy or possible to measure directly because we can’t go there.”
The findings have implications for how humans keep time and for how we position satellites in space.
“If you want to fly a new mission to Mars, for example, we really need to know exactly what the state of Earth is in space, and if that changes, we might actually make a navigation error or a mistake,” Soja said.
A 1-meter shift in Earth’s axis, for example, could mean a spacecraft misses its target by 100 or 1,000 meters when it reaches Mars.
As for timekeeping, research published in March suggests that climate change has delayed the need to add a “negative leap second” to Coordinated Universal Time to keep world clocks in line with Earth’s rotation.
Duncan Agnew, a geophysicist at UC San Diego’s Scripps Institution of Oceanography 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 achieved a result similar to his.
“Multiple discoveries are almost the rule in science — this is another case in point,” Agnew said.
Thomas Herring, a professor of geophysics at MIT who was not involved in either study, said the new research could really offer insight into how changes on Earth’s surface can affect what’s going on inside.
“For the feedback between surface processes and the core, I find that plausible,” Herring said in an email, explaining that “large-scale” surface processes can “penetrate to the liquid core.”
