Recent shifts in Earth’s magnetic field now show human fingerprints. Our planet’s magnetic poles normally wander sporadically. Yet, new research reveals a surprising cause. We have amassed enough water behind dam walls. This accounts for at least some current shifts in Earth’s magnetic polepoles movements.
Harvard University geophysicist Natasha Valencic led this research. She and her colleagues calculated significant impacts in nearly 7,000 of Earth’s biggest dams. Their concentrated masses have knocked the crust’s axis. This rotation axis shifted by about one meter. This is relative to the dynamo driving magnetic fields., impacting Earth’s magnetic poles relative to the dynamo driving magnetic fields.
WATER HOARDING AND GLOBAL IMPACTS
What’s more, all this water hoarding caused other effects. It has resulted in a 21-millimeter drop in sea levels. “As we trap water behind dams, not only does it remove water from the oceans,” says Valencic. This leads to a global sea level fall. “It also distributes mass in a different way around the world.” This mass redistribution impacts Earth’s magnetic pole positions. The poles shift relative to the surface.
Adding extra weight to a spinning sphere causes shifts. The weighted part pulls towards the equator. This shifts the axis around which the sphere spins. Redistributing Earth’s surface weight re-orientates its spin axis. ThisEarth’s magnetic poles are occursaffected whether from damming water, melting glaciers or groundwater removal.
However, only Earth’s outer crust floats and shifts. It moves over its gooey inner parts. The inner “goo” generates the magnetic field. This shifting leads to a different surface part sitting over our inner magnetic north. North itself has not truly moved in space. Earth’s surface has simply shifted over it. This phenomenon is called true polar wander and affects Earth’s magnetic poles.
TRACKING THE NORTH POLE’S JOURNEY
Valencic and her team tracked the North Pole’s shift. It moved in two distinct phases. From 1835 to 1954, it shifted eastward. This movement was towards Russia. It covered about 20 centimeters (8 inches). Dams built in Europe and North America caused this. Then, from 1954 to 2011, it moved westward. The pole shifted 57 centimeters (22 inches) towards North America. More dams built in Asia and East Africa drove this.
“We’re not going to drop into a new ice age,” Valencic explains. “The pole moved by about a meter in total.” However, this shift “does have implications for sea level.” Researchers calculated a significant impact. We have trapped a quarter of this century’s sea level rise behind dams. This equates to about 1.2 millimeters per year.
FUTURE IMPLICATIONS FOR SEA LEVEL RISE
In some ways, this could seem beneficial. Human-induced climate change causes sea levels to rise. This already creates damaging tidal surges. Increasingly turbulent atmospheric storms contribute to this. Yet, these findings demand careful consideration. They must be included in future sea level rise estimates.
“Depending on where you place dams and reservoirs, the geometry of sea level rise will change,” Valencic cautions. “That’s another thing we need to consider.” These changes can be “pretty large, pretty significant.”
Shifting Earth’s magnetic poles add to a growing list. Humans are inadvertently altering planetary phenomena. This includes shrinking atmospheric layers. We are also altering ocean circulation. Even activating volcanoes shows human influence. This groundbreaking research was published in Geophysical Research Letters.