Climate Change’s Impact on Day Length
Climate change is melting Greenland and Antarctic ice, redistributing water to the equatorial regions, and altering Earth’s rotation, lengthening days by a few milliseconds. NASA-funded ETH Zurich researchers demonstrated that this impact might outperform the moon’s influence on Earth’s rotational speed while also changing the Earth’s axis of rotation.
Melting polar ice caused by climate change is redistributing Earth’s mass, slowing its rotation and somewhat prolonging the day, according to NASA-funded research at ETH Zurich. This shows that humans have a greater influence on Earth’s rotational dynamics than previously thought.
Climate change is melting the ice in Greenland and Antarctica. As a result, water from these arctic locations flows into the world’s oceans, particularly the equatorial zone. “This means that a mass shift is taking place, affecting the Earth’s rotation,” says Benedikt Soja, Professor of Space Geodesy at ETH Zurich’s Department of Civil, Environmental, and Geomatic Engineering.
Mass Redistribution and Earth’s Axis
“It’s like when a figure skater does a pirouette, first holding her arms close to her body and then stretching them out,” Soja tells me. The initial quick rotation slows as the masses migrate away from the axis of rotation, increasing physical inertia. We talk about the law of conservation of angular momentum in physics, which also governs the Earth’s rotation. When the Earth rotates more slowly, the days become longer. Climate change is also affecting the day on Earth, albeit only slightly.
With support from the US space agency NASA, the ETH researchers from Soja’s group have published two new studies in the journals Nature Geoscience and Proceedings of the National Academy of Sciences (PNAS) on how climate change impacts pole motion and daylight hours.
As per the PNAS study, ETH Zurich researchers found that climate change is increasing the length of the day by a few milliseconds from its current 86,400 seconds. This is because water flows from the poles to lower latitudes, reducing the speed of rotation.
The Moon’s Role in Earth’s Rotational Speed
The moon also aids in this delay through tidal friction. However, the new study comes to an unexpected conclusion: if humans continue to emit more greenhouse gases and the Earth warms accordingly, this will eventually have a greater influence on the Earth’s rotational speed than the effect of the moon, which has determined the length of the day for billions of years.
Despite that, variations in mass on the Earth’s surface and interior produced by melting ice modify not just the Earth’s rotational speed and length of day, but also the axis of rotation, as the researchers demonstrate in Nature Geoscience. This means that the sites where the axis of rotation intersects the Earth’s surface move. Researchers may monitor this pole motion, which averages about 10 meters per hundred years over a longer span.
Not only is ice sheet melting involved, but so are internal Earth movements. Long-term displacements occur deep in the Earth’s mantle, where the rock becomes viscous as a result of tremendous pressure. There are additional heat flows in the liquid metal of the Earth’s outer core, which generate the magnetic field and cause mass shifts.
In the most extensive modeling to date, Soja and his team have demonstrated how polar motion is caused by distinct mechanisms in the core, mantle, and surface climate. The work was recently published in the journal Nature Geoscience. “For the first time, we present a complete account for the causes of long-period polar motion,” says Mostafa Kiani Shahvandi, a Soja doctorate student and the study’s main author. “In other words, we now know why and how the Earth’s axis of rotation moves relative to the Earth’s crust.”
One discovery in particular shines out from their study in Nature Geoscience: the activities on and inside the Earth are interrelated and influence one another. “Climate change is making the Earth’s axis of rotation move, and it shows that the reaction from the conservation of angular momentum is also changing the dynamics of the Earth’s core,” Soja tells me. Kiani Shahvandi concurs: “Ongoing climate change could therefore even be affecting processes deep inside the Earth and have a greater reach than previously assumed.” However, there is minimal reason for alarm because these effects are modest and unlikely to represent a risk.
Modeling Polar Motion with AI
To study polar motion, the researchers used physics-informed neural networks. Given that these are the latest artificial intelligence (AI) methodologies in which researchers use physical laws and principles to make very powerful and solid machine learning algorithms. Kiani Shahvandi was assisted by Siddhartha Mishra, Professor of Mathematics at ETH Zurich, who in 2023 got ETH Zurich’s Rössler Prize, the university’s most heavily funded research prize, and is a specialist in this line.
Kiani Shahvandi’s methods enabled the first recording of all the various outcomes on the Earth’s surface, mantle, and core, as well as the modeling of their potential interactions. The results of the computations illustrate how the Earth’s rotating poles have migrated since 1900. These model values are in great agreement with genuine data provided by historical astronomical observations and satellites during the last thirty years, allowing for future forecasts.
Implications for Space Navigation
“Even if the Earth’s rotation is changing only slowly, this outcome has to be taken into record when navigating in space – for instance, when sending a space probe to land on another planet,” adds Soja. Even a tiny variation of one centimeter on Earth can result in a deviation of hundreds of meters over long distances. “Otherwise, it won’t be possible to land in a specific crater on Mars,” he claims.