The role of climate change on Earth’s polar motion and the length of day

Modern climate change has triggered large-scale lateral mass transport between land and the oceans. Indeed, satellite observations suggest unprecedented melting of global glaciers and polar ice sheets, large spatiotemporal variability of terrestrial water storage, sustained dwindling of groundwater resources, and rising global and regional sea levels. We have investigated the impact of this climate-driven surface mass redistribution on the planetary-scale phenomenon of Earth’s rotation and reported the key findings in three papers published recently in Nature Geoscience (https://doi.org/10.1038/s41561-024-01478-2), PNAS (https://doi.org/10.1073/pnas.2406930121), and Geophysical Research Letters (https://doi.org/10.1029/2024GL111148). This presentation will showcase these new results, discuss their implications, and underscore the need for continued geodetic observations to advance climate research.

The first part of this presentation is focused on the polar motion—the motion of the Earth’s spin axis relative to the crust—and provides a first cohesive interpretation of the 120-year-long data. Our analysis unravels the critical roles of climatological processes, particularly in modulating the polar motion on interannual to multidecadal timescales. We disentangle polar motion signals to uniquely constrain global-scale hydrological models. We also tease out a systematic anticorrelation between the climatological and core processes, hinting at the two-way coupling between Earth’s surficial and deep-interior processes—an intriguing multidisciplinary topic for further exploration.

Next, we will examine more than 40 years of Earth’s oblateness (J2) data and nearly 3000 years of eclipse data to evaluate the impact of climate change on length of day (LOD) variations. We show that the rate of LOD change in the past two decades (+1.3 milliseconds/century) is the greatest since the onset of modern climate change. Under high-end emission scenarios, this rate could double and surpass the tidal friction contribution (+2.4 milliseconds/century), highlighting the planetary-scale impact of modern climate change. We also derive an independent estimate of the glacial isostatic adjustment signal, which, when added to the tidal friction signal, fully reconciles the secular LOD trend derived from the ancient eclipse data, diminishing the possible contribution of core processes on secular timescales. We show, on the other hand, that in the preindustrial era the role of climatic oscillations was subdominant. In fact, by using archaeomagnetic and more modern geomagnetic data and using the simple principles of magnetohydrodynamics, we demonstrate that fluid motion in the Earth's core explains the decadal and millennial fluctuations observed in LOD record. Our results present a consistent explanation for the long-period polar motion and LOD and have considerable implications for internal and external geodynamics.