How climate change affects the Earth’s rotation and length of day
The redistribution of mass due to melting ice sheets, ice shelves and glaciers has an influence on the Earth’s rotation, affecting the length of the day and the position of the rotational axis.
The rapid melting of the polar ice masses in Greenland and Antarctica is leading to a considerable shift in mass on the Earth’s surface. Two new studies led by ETH Zurich, which were published yesterday in Proceedings of the National Academy of Sciences and last Friday in Nature Geoscience, describe the effects of this redistribution on the Earth’s rotation and the rotational axis.
In the first study, Benedikt Soja, Professor of Space Geodesy at the Department of Civil, Environmental and Geomatic Engineering at ETH Zurich, and his team focused on the influence of climate change on the Earth’s rotation speed and found that the days on Earth are getting longer due to climate change. However, it is only a matter of a few milliseconds added to the current 86,400 seconds.
The reason for the increase in the length of the day lies in the mass shift caused by the loss of ice, whereby the meltwater is distributed in the global ocean, but mainly concentrates in the equatorial region.
Professor Soja describes the effect in a university press release using a well-known example: “It’s like when a figure skater does a pirouette, first holding her arms close to her body and then stretching them out.” The speed of the rotation decreases as soon as the masses move away from the rotational axis. This is based on the physical law of conservation of angular momentum, which is also followed by the Earth’s rotational movement, which slows down and thus makes the days longer. Although the changes are only minimal and imperceptible to us, the new results illustrate the influence that climate change, and therefore we humans, have on such large natural features.
A natural cause of the slowing of the Earth’s rotation and the increase in length of day that has existed for billions of years is the tidal friction induced by the moon. However, the study now concludes that the slowdown caused by climate change would have a greater effect on the Earth’s rotational speed than the moon if carbon emissions remain high.
“We humans have a greater impact on our planet than we realise,” says Professor Soja, “and this naturally places great responsibility on us for the future of our planet.”
The rotational axis moves
In their second study, published in Nature Geoscience, the research team, also led by Professor Soja, uses artificial intelligence – so-called physics-informed neural networks – to describe that the Earth’s rotational axis is also shifting due to climate change.
During polar motion, which also occurs naturally, the points at which the axis of rotation meets the Earth’s surface move. Researchers are observing a movement of around 10 meters per century, which is not only due to the loss of ice masses, but also to shifts deep in the Earth’s mantle that occur over longer periods of time. Mass shifts also occur in the Earth’s outer core, where heat flows move liquid metal.
Never before has it been possible to show how the migration of the poles is caused by the various processes in the Earth’s core and mantle and by climate change. “For the first time, we present a complete explanation for the causes of long-period polar motion,” says Mostafa Kiani Shahvandi, Professor Soja’s doctoral student and first author of both studies. “In other words, we now know why and how the Earth’s axis of rotation moves relative to the Earth’s crust.”
Particularly remarkable is the finding that the surface processes are linked to those deep below the Earth’s surface influencing each other. “Climate change is causing the Earth’s axis of rotation to move, and it appears that the feedback from the conservation of angular momentum is also changing the dynamics of the Earth’s core,” explains Professor Soja.
Kiani Shahvandi adds that the ongoing climate change could even affect processes deep inside the Earth and reach further than previously assumed.
The research team’s model calculations, which reconstruct the movements of the Earth’s rotational poles since 1900, are so accurate that they agree very well with real observations, allowing predictions for the future.
Minor effects on Earth, major impact on space travel
Professor Soja concludes by noting that the changes in the Earth’s rotation must be taken into account when navigating in space, “for example, when sending a space probe to land on another planet.” What is a deviation of just one centimeter on Earth adds up to deviations of several hundred meters over the huge distances involved. “Otherwise, it won’t be possible to land in a specific crater on Mars.”
Julia Hager, Polar Journal AG
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