How climate change is altering the Earth's rotation

For the first time, researchers have been able to fully explain the various causes of long-term polar motion in the most comprehensive modeling to date, using AI methods. Their model and their observations show that climate change and global warming will have a greater influence on the Earth's rotational speed than the effect of the moon, which has determined the increase in the length of the day for billions of years.

Climate change is causing the ice masses in Greenland and Antarctica to melt. Water from the polar regions is flowing into the world's oceans—and especially into the equatorial region.

This means that a shift in mass is taking place, and this is affecting the Earth's rotation.

It's like when a figure skater does a pirouette, first holding her arms close to her body and then stretching them out. The initially fast rotation becomes slower because the masses move away from the axis of rotation, increasing physical inertia.

In physics, we speak of the law of conservation of angular momentum, and this same law also governs the Earth's rotation. If the Earth turns more slowly, the days get longer. Climate change is therefore also altering the length of the day on Earth, albeit only minimally for now.

Another cause of this slowdown is tidal friction, which is triggered by the moon. However, the new study comes to a surprising conclusion: if humans continue to emit more greenhouse gases and the Earth warms up accordingly, this would ultimately have a greater influence on the Earth's rotational speed than the effect of the moon, 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 and this naturally places great responsibility on us for the future of our planet.

However, shifts in mass on the Earth's surface and in its interior caused by the melting ice not only change the Earth's rotational speed and the length of day: as the researchers show in Nature Geoscience, they also alter 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 motion, which, over a longer timeframe, comes to some ten meters per hundred years. It's not only the melting of the ice sheets that plays a role here, but also movements taking place in the Earth's interior.

Deep in the Earth's mantle, where the 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 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, researchers have now shown how polar motion results from individual processes in the core, in the mantle and from the climate at the surface.
One finding in particular that stands out in their study is that the processes on and in the Earth are interconnected and influence 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.
Ongoing climate change could therefore even be affecting processes deep inside the Earth and have a greater reach than previously assumed. However, there is little cause for concern, as these effects are minor and it's unlikely that they pose a risk.
Implications for space travel
Even if the Earth's rotation is changing only slowly, this effect has to be taken into account when navigating in space—for example, when sending a space probe to land on another planet. Even a slight deviation of just one centimeter on Earth can grow to a deviation of hundreds of meters over the huge distances involved.

"Otherwise, it won't be possible to land in a specific crater on Mars".

 Kiani Shahvandi, Mostafa, The increasingly dominant role of climate change on length of day variations, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2406930121. doi.org/10.1073/pnas.2406930121

Mostafa Kiani Shahvandi et al, Contributions of core, mantle and climatological processes to Earth's polar motion, Nature Geoscience (2024). DOI: 10.1038/s41561-024-01478-2. www.nature.com/articles/s41561-024-01478-2