If Earth continues to warm, climate change will have a greater impact on the speed of our planet’s rotation in the future than the Moon does now, according to a recent study by ETH Zurich supported by NASA.

The melting of ice masses in Greenland and Antarctica is causing water from the polar regions to flow into the world’s oceans, especially toward the equatorial region. This mass displacement is affecting Earth’s rotation, explains Benedikt Soja, professor of Space Geodesy in the Department of Civil, Environmental, and Geomatic Engineering at ETH Zurich.

It’s similar to a figure skater extending their arms during a spin: the initially fast rotation slows down as the masses move away from the axis of rotation, increasing physical inertia, says Soja. This slowing of Earth’s rotation means that days are getting longer, although only minimally.

In their study published in Proceedings of the National Academy of Sciences (PNAS), the researchers from ETH Zurich show that climate change is increasing the length of the day by a few milliseconds. This is because water flows from the poles to lower latitudes, thereby slowing down the rotation speed.

Although tidal friction caused by the Moon also contributes to this deceleration, the new study concludes that if humans continue to emit more greenhouse gases, global warming would have a greater impact on Earth’s rotation speed than the Moon, which has influenced the length of the day for billions of years.

The polar movement describes the movement of the Earth’s axis of rotation (shown in orange) with respect to the north and south geographical poles (shown in blue)

Humans have a greater impact on our planet than we think, states Soja. This places a great responsibility on us for the future of our planet.

Another study published in Nature Geoscience reveals that mass changes on Earth’s surface and interior, caused by ice melt, also alter the axis of rotation. This means that the points where the axis of rotation meets Earth’s surface move, a phenomenon researchers can observe as polar motion.

These movements are not only due to the melting of ice sheets but also to shifts in the Earth’s mantle and heat flows in the outer core. The most comprehensive modeling to date by Soja and his team shows how these individual processes in the core, mantle, and surface affect polar motion.

For the first time, we present a complete explanation of the causes of long-term polar motion, says Mostafa Kiani Shahvandi, doctoral student and lead author of the study. We now know why and how the axis of Earth’s rotation moves relative to the Earth’s crust.

The team used physics-informed neural networks, a novel artificial intelligence methodology, to develop especially powerful and reliable machine learning algorithms. Kiani Shahvandi was supported by Siddhartha Mishra, professor of Mathematics at ETH Zurich and specialist in this field.

Soja concludes: Climate change is moving Earth’s axis of rotation, and it seems that feedback from the conservation of angular momentum is also changing the dynamics of the Earth’s core. Kiani Shahvandi adds: Ongoing climate change could affect even the processes inside the Earth more than previously thought, although these effects are minor and unlikely to represent a risk.

SOURCES

ETHZürich

Kiani Shahvandi M, Adhikari S, et al., Contributions of core, mantle and climatological processes to Earth’s polar motion. Nature Geoscience, Vol. 17, July 2024, p. 705–710. DOI:doi.org/10.1038/s41561-024-01478-2

Kiani Shahvandi M, Adhikari S, Dumberry M, et al., The increasingly dominant role of climate change on length of day variations. Proceedings of the National Academy of Sciences, PNAS 2024, Vol. 121, No. 30, e2406930121. DOI:doi.org/10.1073/pnas.2406930121

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