Impact of Human Activity on Earth's Rotation Revealed by Scientists

Recent research published in the journal Geophysical Research Letters has revealed that human activities, particularly the construction of large dams, have caused a measurable shift in the Earth's rotational axis. This shift, while small—estimated at approximately 3.7 feet over the past two centuries—has significant implications for our understanding of geophysical dynamics and climate change.

According to the study led by Natasha Valencic, a graduate student in the Department of Earth and Planetary Sciences at Harvard University, the mass redistribution caused by these dams has influenced the phenomenon known as true polar wander. This phenomenon is essential for accurate navigation and timekeeping technologies such as GPS, and affects astronomical observations as well.

Valencic elaborated, "Imagine a spinning balloon with a fly landing on it. The pole will move away from the extra mass, which is analogous to what is happening with Earth due to dam construction." The study analyzed data from nearly 7,000 dams built globally from 1835 to 2011, which collectively hold enough water to fill the Grand Canyon twice. The researchers focused on dams containing at least one cubic kilometer of water, as smaller dams were deemed to have a negligible impact on the study's results.

The findings indicate that the construction of these dams has resulted in a shift of the North Pole, particularly between 1835 and 1954, when most dam activity was concentrated in North America. During this period, the North Pole moved about eight inches toward the 103rd meridian east, which traverses Eurasia. From the 1950s to 2011, the focus shifted to East Africa and Asia, leading to an additional 22-inch shift toward the 117th meridian west, which passes through North America.

While the contribution of dams to polar wander is relatively minor in comparison to factors such as ice melt and mantle convection, it remains a vital component of the overall geophysical budget. Valencic noted, "It is actually a pretty big debate—how important convection is, as opposed to ice melting and other phenomena, like dams. Dams are a smaller contribution to polar wander; maybe an order of magnitude smaller than ice melt. But still, it's important to close the budget."

The implications of these findings extend beyond mere academic interest. Human-driven climate change is accelerating the loss of glaciers and ice sheets, which contributes to sea level rise and further influences polar wander. As Valencic explained, the movement of the geographic poles affects sea levels in different hemispheres, with one hemisphere experiencing a rise while the opposite sees a fall. This complex interplay between human activity and natural processes underscores the need for a holistic understanding of Earth's climate system.

Moreover, recent studies have indicated that human-induced shifts in ice and groundwater are slowing Earth's rotation at a pace of 1.33 milliseconds per century. This slow-down may eventually outweigh the Moon's tidal influence on Earth's rotation. Notably, China's Three Gorges Dam, the largest in the world, is estimated to account for a rotational slowdown of 0.06 microseconds and a polar shift of 0.8 inches when filled to capacity.

In light of these developments, Valencic concluded, "If we want to fully understand polar wander, and what's going on with the axis, we need to pin everything down." As climate change continues to reshape our planet, the intricate connections between human activity and geophysical dynamics demand ongoing research and public awareness.