How Human Activity is Shifting Earth’s Magnetic Field
Recent research has revealed that human activity, particularly the construction of large dams, is contributing to shifts in Earth’s magnetic field. While it is normal for the planet’s magnetic poles to move sporadically, the accumulation of water behind dam walls is now being identified as a significant factor in these movements.
Harvard University geophysicist Natasha Valencic and her team have calculated that the mass stored in approximately 7,000 of the world’s largest dams has caused a deviation of around one meter in the Earth’s crust’s axis of rotation. This shift is relative to the dynamo that generates the magnetic fields beneath the Earth’s crust.
Furthermore, the impact of this water storage has led to a drop of 21 millimeters in global sea levels. Valencic explains, “As we trap water behind dams, it not only reduces water in the oceans, resulting in a decrease in sea levels, but it also redistributes mass unevenly around the planet.”
This redistribution of mass can influence the positions of Earth’s magnetic poles in relation to its surface. When additional weight is added to a rotating sphere, it tends to shift the weighted part towards the equator, altering the axis around which the sphere rotates. Therefore, changes in Earth’s surface weight can lead to a reorientation of its spin axis, whether through damming water, glacier melting, or groundwater extraction.
However, it is crucial to note that only the Earth’s outer crust, which floats above its molten interior, is subject to these shifts. The inner core responsible for generating the magnetic field remains stable, resulting in a shift of Earth’s surface over the inner magnetic pole. This phenomenon is known as true polar wander.
The research by Valencic and her team indicates that the North Pole has shifted in two phases. Between 1835 and 1954, it moved eastward towards Russia by approximately 20 centimeters, coinciding with dam construction in Europe and North America. Subsequently, from 1954 to 2011, the pole shifted 57 centimeters west towards North America as more dams were built in Asia and East Africa.
While the total movement of the pole is relatively small, Valencic emphasizes its implications for sea level rise. The researchers estimate that dams have so far captured a quarter of the sea level rise observed this century, which amounts to about 1.2 millimeters per year.
Considering the ongoing threat of rising sea levels due to climate change, the ability to mitigate some of this rise through damming water could be seen as a positive outcome. However, it is essential to factor in these findings when projecting future sea level rise and its potential impacts on coastal regions.
These findings highlight the interconnected nature of human activities and their effects on global phenomena such as Earth’s magnetic field. As we continue to alter the planet through various means, it is crucial to understand and account for the repercussions of these actions on the Earth’s natural systems.
This study was published in Geophysical Research Letters.
