New publications by Kiani Shahvandi et al. (2024)

The group of Space Geodesy at ETH Zurich has led two studies related to polar motion and the length of day, with the focus on quantifying the influence of ongoing climate change. Mostafa Kiani Shahvandi and Benedikt Soja collaborated with researchers from the Department of Mathematics at ETH Zurich, Jet Propulsion Laboratory at NASA, University of Alberta, Federal Agency for Cartography and Geodesy in Germany, German Research Center for Geosciences, and Institute of Geodesy and Geoinformation Science at TU Berlin. In the first study published in the journal Nature Geoscience, the researchers have unraveled the causes of long-period polar motion since 1900 (see figure below). The primary conclusion of this study is that the climatic effects---namely the melting of polar ice sheets and global glaciers, as well as terrestrial water storage---are the main driver of long-period polar motion. In addition, the influence of mantle and core dynamics is analyzed and used to explain the secular trend in the polar motion observations. To achieve this goal, the researchers used Artificial Intelligence techniques.

In the second study published in the journal Proceedings of the National Academy of Sciences, the researchers investigated the influence of ongoing climate change on the variations in the length of the day. As the length of the day is tied to the Earth's rotation, any processes that impact the rotation rate of the Earth will change the duration of a day. The melting of polar ice sheets and global glaciers, as well as variations in terrestrial water will result in the rise of sea level and increase in the Earth's oblateness. The principle of conservation of angular momentum implies that the more oblate a figure is the harder it is to rotate it. Therefore, climate change will result in the slowing down in Earth's rotation, which is turn increases the length of the day. Although only on the order of a few milliseconds per century, the impact can increase significantly and even surpass the effect of Earth-Moon dynamics. This will have implications for precise timekeeping, including the introduction of leap seconds and the navigation of satellites.