Climate change is causing the Greenland and Antarctic ice sheets to melt, moving water into the equatorial regions and affecting the Earth’s rotation, which lengthens days by a few milliseconds. ETH Zurich researchers, supported by NASA, have shown that this impact could overcome the Moon’s influence on the Earth’s rotation rate and also shifts the Earth’s spin axis.
Melting polar ice due to climate change is redistributing the Earth’s mass, slowing its rotation and slightly lengthening the day, ETH Zurich-backed studies highlight NASA. This indicates a greater human influence on Earth’s rotational dynamics than previously known.
Climate change is leading to melting of ice in Greenland and Antarctica. As a result, water from these polar regions flows into the world’s oceans—and especially into the equatorial region. “This means that there is a displacement of mass and this affects the rotation of the Earth,” explains Benedikt Soja, Professor of Space Geodesy at the Department of Civil, Environmental and Geomatics Engineering at ETH Zurich.
“It’s like a figure skater doing a pirouette, first holding her arms close to her body and then extending them,” says Soja. The initially fast rotation slows down as the masses move away from the axis of rotation, increasing physical inertia. In physics, we talk about the law of conservation of angular momentum, and the same law also governs the rotation of the Earth. If the Earth rotates more slowly, the days get longer. Climate change therefore also changes the length of the day on Earth, albeit only minimally.
With the support of the US space agency NASA, ETH researchers from the Soja group have published two new studies in journals. Nature Geoscience and Proceedings of the National Academy of Sciences (PNAS) on how climate change affects polar motion and day length.
Climate change exceeds the influence of the moon
In the PNAS study, ETH Zurich researchers show that climate change is also extending the length of the day by a few milliseconds from the current 86,400 seconds. This is because water flows from the poles to lower latitudes and thus slows the rate of rotation.
Another cause of this deceleration is tidal friction, which is triggered by the Moon. But the new study comes to a surprising conclusion: if humans continue to emit more greenhouse gases and the Earth warms accordingly, it will eventually have a greater effect on the Earth’s rotation rate than the influence of the Moon, which has determined the increase in day length for billions of years. “We humans have a greater influence on our planet than we realize,” concludes Soja, “and this naturally places upon us a great responsibility for the future of our planet.”
The rotation axis of the Earth is shifting
However, mass shifts on the Earth’s surface and in its interior caused by melting ice do not only change the speed of the Earth’s rotation and the length of the day: as scientists show in Nature Geoscience, also changes the rotation axis. This means that the points where the axis of rotation actually meets the Earth’s surface are moving. Researchers can observe this polar movement, which on a longer time horizon is around ten meters per hundred years. Not only the melting of ice sheets plays its role here, but also the movements taking place inside the Earth. Deep in the Earth’s mantle, where rock becomes viscous due to high pressure, displacements occur over long periods of time. And there are also heat flows in the liquid metal of the Earth’s outer core that are responsible for generating the Earth’s magnetic field and leading to mass movements.
In the most comprehensive modeling to date, Soja and his team have now shown how polar motion results from individual processes in the core, mantle, and surface climate. Their study was recently published in the journal Nature Geoscience. “For the first time, we present a complete explanation of the causes of long-term polar motion,” says Mostafa Kiani Shahvandi, one of Soja’s PhD students and lead author of the study. “In other words, we now know why and how the Earth’s spin axis moves relative to the Earth’s crust.”
One insight in particular stands out in their study Nature Geoscience: that processes on and in the Earth are interconnected and mutually influencing. “Climate change causes the Earth’s rotation axis to move, and the feedback from the conservation of angular momentum also appears to change the dynamics of the Earth’s core,” explains Soja. Kiani Shahvandi adds: “Ongoing climate change could therefore even affect processes deep inside the Earth and be more far-reaching than previously thought.” However, there is little cause for concern as these effects are small and unlikely to pose a risk.
Physical laws combined with artificial intelligence
For their study of polar motion, the researchers used what are known as physics-informed neural networks. These are new Artificial Intelligence (AI) methods in which researchers apply the laws and principles of physics to develop particularly powerful and reliable algorithms machine learning. Kiani Shahvandi received support from Siddhartha Mishra, Professor of Mathematics at ETH Zurich, recipient of the 2023 ETH Zurich Rössler Prize, the university’s highest-funded research award, and a specialist in the field.
The algorithms that Kiani Shahvandi developed made it possible for the first time to record all the different effects on the Earth’s surface, in its mantle and in its core, and to model their possible interactions. The result of the calculations shows how the rotation poles of the Earth have shifted since 1900. These model values ​​are in excellent agreement with the real data provided by astronomical observations in the past and satellites over the last thirty years, which means that they also allow predictions for the future.
Important for space travel
“Even if the Earth’s rotation changes only slowly, this effect must be taken into account when navigating in space – for example, when sending a space probe to land on another planet,” says Soja. Even a tiny deviation of just one centimeter on Earth can grow to a deviation of hundreds of meters over long distances. “Otherwise it won’t be possible to land in a particular crater. Mars,” he says.
Reference:
“The Still Dominant Role of Climate Change on Day Length Changes” by Mostafa Kiani Shahvandi, Surendra Adhikari, Mathieu Dumberry, Siddhartha Mishra, and Benedikt Soja, 15 July 2024. Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2406930121
Mostafa Kiani Shahvandi, Surendra Adhikari, Mathieu Dumberry, Sadegh Modiri, Robert Heinkelmann, Harald Schuh, Siddhartha Mishra, and Benedikt Soja, “Contributions of core, mantle, and climatological processes to the Earth’s polar motion,” 12 July 2024, Nature Geoscience.
DOI: 10.1038/s41561-024-01478-2