Humans surpass the Moon in influencing the Earth

Climate change is leading to melting ice in Greenland (Arctic) and Antarctica. As a result, melt water from these polar regions is flowing into the world's oceans – and especially into the equator. Benedikt Soja, Professor of Spatial Geodesy at the Department of Civil, Environmental and Geological Engineering at ETH Zurich, explains: 'This means that a change in mass distribution is taking place and is affecting to the rotation of the Earth'.

'It's like when a figure skater does a spin, first keeping the arms pressed against the body and then stretching them out,' says Soja. The initially fast rotation becomes slower as the mass of the arm moves away from the axis of rotation, increasing physical inertia. In physics, we talk about the law of conservation of angular momentum and this law also governs the Earth's rotation. If the Earth rotated more slowly, the days would be longer. Therefore, climate change is also changing the length of the day on Earth, although only minimally."

Supported by the US space agency NASA, ETH researchers from Soja's team published two new studies in Nature Geoscience and Proceedings of the National Academy of Sciences (PNAS) on how to transform Climate affects polar movements and day length.

Climate change surpasses the influence of the moon

In a study on PNAS, ETH Zurich researchers show that climate change is also increasing the length of the day by a few milliseconds from the current 86,400 seconds. This is because water is flowing from the poles to lower latitudes, thereby slowing down the rate of rotation according to the law of conservation of angular momentum.

Another cause of this slowing is tidal friction caused by the moon. However, new research comes to a surprising conclusion: if humans continue to emit more greenhouse gases and the Earth warms accordingly, we will eventually have an effect on the planet's rotation rate. The Earth is larger than the moon's impact, which has been the determining factor in the increase in day length over billions of years. Soja concludes: 'We humans have a greater impact on our planet than we realize and this naturally places great responsibility on humanity for the future of the planet.'

The Earth's axis of rotation is shifting

However, the change in mass on the Earth's surface and within it caused by melting ice does not only change the Earth's rotation speed and day length, as researchers point out in the journal Nature Geoscience. Notably, they also change the axis of rotation, meaning that the conventional endpoint of the axis of rotation on the Earth's surface actually moves.

Researchers can observe this polar motion, over long periods of time. Movement speed can reach about ten meters in one hundred years. Here not only the melting of ice plays an important role, but also the movements taking place inside the Earth. Deep in the Earth's crust, where rocks are viscous due to high pressure, displacement occurs over long periods of time. And there are heat currents in the liquid metal of Earth's outer core, which both create Earth's magnetic field and lead to mass displacement.

In the most comprehensive model to date, Soja and his team have now shown that polar motion results from individual processes in the core, in the mantle, and from the climate at the surface. Their research was recently published in the journal Nature Geoscience.

Mostafa Kiani Shahvandi, one of Soja's PhD students and lead author of the study, said: 'For the first time, we provide a full explanation of the cause of polar motion in time. long. In other words, we now know why and how the Earth's rotation axis moves relative to the Earth's crust'.

One particularly striking finding in their study in the journal Nature Geoscience states that processes in and on Earth are interconnected and influence each other. 'Climate change is causing the Earth's rotation axis to move, and it seems that feedback from the conservation of angular momentum is also changing the dynamics of the Earth's core,' Soja explains.

Kiani Shahvandi added: 'Therefore, ongoing climate change may even affect processes deep inside the Earth and have a larger scope of influence than previously assumed.' However, there is little reason for concern as these effects are small and it is unlikely that they pose a risk.

The laws of physics combined with artificial intelligence

To study polar motion, researchers used physics-informed neural networks. This is a new artificial intelligence (AI) method in which researchers apply the laws and principles of physics to develop exceptionally powerful and reliable algorithms for the receiving computer. Kiani Shahvandi has received support from Siddhartha Mishra, Professor of Mathematics at ETH Zurich, who in 2023 received ETH Zurich's Rössler Prize, the university's highest research award, and of which Mishra is also an expert. engaged in this field.

The algorithms that Kiani Shahvandi developed for the first time have made it possible to capture all the different effects on the Earth's surface, in its mantle and in its core, and to model the interactions that may arise. The calculation results show how the Earth's rotation poles have shifted since 1900. These model values ​​agree well with real data provided by past astronomical observations and by satellites over the past thirty years. From there, we can believe that Shahvandi's algorithm also allows forecasting the future.

Important for space travel

Soja said: 'Even if the Earth's rotation changes only slowly, this effect must still be taken into account when navigating through space – for example, when we send a space probe to land on a planet other'. Even a small error of just one centimeter on Earth can add up to an error of hundreds of meters over the very large distances involved. "If we don't (take into account changes on Earth), we won't be able to land a probe in a specific crater on Mars," he said.

Micah Soto

Update 19 July 2024