Climate change is melting ice in Greenland and Antarctica, moving water toward the equatorial regions and affecting the Earth’s rotation, lengthening the days by a few milliseconds. With support from NASA, researchers at ETH Zurich showed that this impact could exceed the Moon’s influence on the Earth’s rotation rate and also shift the Earth’s rotational axis.
The melting of polar ice due to climate change is redistributing the Earth’s mass, slowing its rotation and making the day slightly longer, as shown by studies from ETH Zurich, supported by NASAThis suggests that humans have a greater influence on the Earth’s rotational dynamics than previously assumed.
Climate change is causing ice to melt in Greenland and Antarctica. As a result, water from these polar regions is flowing into the world’s oceans – particularly in the equatorial region. “This means that there is a shift in mass, and this affects 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,” Soja says. The initially fast rotation slows down because the masses move away from the axis of rotation, increasing the physical inertia. In physics, we call it the law of conservation of angular momentum, and this law also governs the rotation of the Earth. As the Earth spins more slowly, the days get longer. So climate change also changes the length of the Earth’s day, albeit only minimally.
With the support of the American space agency NASA, the ETH researchers from Soja’s group have published two new studies in the journals Nature Geosciences And Proceedings of the National Academy of Sciences (PNAS) on how climate change affects polar motion and the length of the day.
Climate change exceeds the influence of the moon
In the PNAS study, the researchers from ETH Zurich show that climate change also increases 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, which slows down the rotation speed.
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 could eventually have a greater effect on the Earth’s rotational speed than the effect of the moon, which has been determining 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 of course places a great responsibility on us for the future of our planet.”
The Earth’s rotational axis shifts
However, shifts in mass on the Earth’s surface and in its interior caused by melting ice do not only change the Earth’s rotational speed and the length of the day: as the researchers show in Nature Geosciencesthey also change the rotation axis. This means that the points where the rotation axis touches the Earth’s surface move. Researchers can observe this polar movement, which amounts to about ten meters per hundred years over a longer period of time. Not only the melting of the ice caps plays a role here, but also movements that take place in the interior of the Earth. Deep in the Earth’s mantle, where the rock becomes viscous due to high pressure, displacements take place 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 both generating the Earth’s magnetic field and leading to shifts in mass.
In the most comprehensive modeling to date, Soja and his team have now shown how polar motion emerges from the individual processes in the core, the mantle, and the surface climate. Their study was recently published in the journal Nature Geosciences. “For the first time, we present a complete explanation for the causes of long-period polar motion,” said Mostafa Kiani Shahvandi, one of Soja’s doctoral students and lead author of the study. “In other words, we now know why and how the Earth’s rotational axis moves relative to the crust.”
One finding in particular stands out in their research Nature Geosciences: that the processes on and in the Earth are interconnected and influence each other. “Climate change is causing the Earth’s rotational axis to move, and it seems that the feedback from the conservation of angular momentum is also changing the dynamics of the Earth’s core,” Soja explains. Kiani Shahvandi adds: “Ongoing climate change could therefore even affect processes deep inside the Earth and have a larger reach than previously thought.” However, there is little reason 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 exceptionally powerful and reliable algorithms for machine learningKiani Shahvandi received support from Siddhartha Mishra, professor of mathematics at ETH Zurich, who received the university’s Rössler Prize in 2023, the university’s highest-ranking research award, and who is a specialist in the field.
The algorithms developed by Kiani Shahvandi have made it possible for the first time to capture all the different effects on the Earth’s surface, in the mantle and in the core and to model their possible interactions. The result of the calculations shows how the Earth’s rotational poles have moved since 1900. These model values correspond excellently to the real data provided by astronomical observations in the past and by satellites in 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 small deviation of just one centimeter on Earth can grow into a deviation of hundreds of meters over the enormous distances. “Otherwise, it is not possible to land in a specific crater Mars,” he says.
References:
“The increasingly dominant role of climate change on day length variations” by Mostafa Kiani Shahvandi, Surendra Adhikari, Mathieu Dumberry, Siddhartha Mishra and Benedikt Soja, July 15, 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2406930121
“Contributions of core, mantle and climatic processes to 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, 2024, Nature Geosciences.
DOI: 10.1038/s41561-024-01478-2