Climate change is slowing the Earth’s rotation

Melting polar ice due to climate change is redistributing Earth’s mass, slowing its rotation and slightly lengthening the day, as highlighted by ETH Zurich studies supported by NASA. This indicates a greater human influence on the dynamics of the Earth’s rotation than previously recognized.

Climate change is leading to the melting of ice in Greenland and Antarctica. As a result, water from these polar regions is flowing into the world’s oceans – and especially in the equatorial region. “This means that a mass shift is taking place and this is affecting the Earth’s rotation,” explains Benedikt Soja, professor of space geodesy at the Department of Civil, Environmental and Geomatic Engineering at ETH Zurich.

“It’s like when a figure skater does a pirouette, first holding her arms close to her body and then extending them,” says Soja. The initially fast rotation becomes slower because the masses move away from the axis of rotation, increasing the 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. Therefore, climate change is also changing the length of the day on Earth, albeit only minimally.

Supported by the US space agency NASA, ETH researchers from Soja’s group have published two new studies in the journal Nature Geoscience AND Proceedings of the National Academy of Sciences (PNAS) on how climate change affects polar motion and day length.

Climate change goes beyond the influence of the moon

In the PNAS study, ETH Zurich researchers show that climate change is also increasing the length of the day by a few milliseconds from its current 86,400 seconds. This is because water flows from the poles at lower latitudes, thus slowing the rate of rotation.

Another cause of this slowdown is tidal friction, which is caused by the moon. However, the new study comes to a surprising conclusion: if humans continue to emit more greenhouse gases and the Earth warms accordingly, this would eventually have a greater impact on the Earth’s rotation speed than the effect of the moon, which which has determined the increase. in the length of the day for billions of years. “We humans have a greater impact on our planet than we realize,” concludes Soja, “and this naturally places great responsibility on us for the future of our planet.”

Earth’s axis of rotation is shifting

However, mass shifts on the Earth’s surface and in its interior caused by melting ice not only change the Earth’s rotation speed and the length of the day: as researchers show in Nature Geoscience, they also change the axis of rotation. This means that the points where the axis of rotation actually meets the Earth’s surface move. Researchers can observe this polar movement, which, over a longer period of time, amounts to about ten meters per hundred years. It is not only the melting of ice sheets that plays a role here, but also the movements that occur in the interior of 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, which are responsible for generating the Earth’s magnetic field and leading to mass displacement.

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 climate at the surface. Their study was recently published in the journal Nature Geoscience. “For the first time, we present a complete explanation for the causes of long-period 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 axis of rotation moves relative to the Earth’s crust.”

One finding in particular stands out in their study Nature Geoscience: that processes in and on Earth are interconnected and influence each other. “Climate change is causing Earth’s spin axis to move, and it appears that feedback from conservation of angular momentum is also changing the dynamics of Earth’s core,” explains Soja. Kiani Shahvandi adds: “Ongoing climate change may affect processes deep within the Earth and have a greater scope than previously assumed.” However, there is little cause for concern as these effects are minor 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 novels artificial intelligence (AI) methods in which researchers apply the laws and principles of physics to develop particularly powerful and reliable algorithms for machine learning. Kiani Shahvandi received support from Siddhartha Mishra, Professor of Mathematics at ETH Zurich, who in 2023 received ETH Zurich’s Rössler Prize, the university’s most recognized award for research and who is a specialist in this field.

The algorithms that Kiani Shahvandi developed have 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, as well as to model their possible interactions. The result of the calculations shows how the rotating poles of the Earth have moved since 1900. These model values ​​are in excellent agreement with the real data provided by astronomical observations in the past and by satellites over the last thirty years, which means that they also enable predictions for the future.

Important for space travel

“Even if the rotation of the Earth is only slowly changing, 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 slight deviation of only one centimeter on Earth can grow to a deviation of hundreds of meters over the large distances involved. “Otherwise, it will not be possible to land in a specific crater March,” he says.

References:

“Increasingly dominant role of climate change in day length variations” 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

“Contributions of nuclear, mantle and climatological processes to the Earth’s polar motion” by Mostafa Kiani Shahvandi, Surendra Adhikari, Mathieu Dumberry, Sadegh Modiri, Robert Heinkelmann, Harald Schuh, Siddhartha Mishra and Benedikt Soja, July 12, 20 Nature Geoscience.
DOI: 10.1038/s41561-024-01478-2