Latest news with #NatashaValencic
Forbes
15-07-2025
- Science
- Forbes
How Humanity's Use Of Water Is Nudging Earth's Tilt
A spinning globe model visualizing how Earth's geographic poles coincide with an imaginary axis ... More around which the planet rotates. In the last 200 years humanity has constructed over 6,800 dams for agricultural use, as drink-water storage and to generate hydroelectric power. Together, they hold so much water that Earth's tilt is changing. Earth's geographic poles, which are the points around which the planet rotates, move with respect to the surface during a process called polar motion in response to the distribution of Earth's mass. The same physical principle can be seen on a much smaller scale during a hammer throw competition, as the swirling mass of the "hammer" — a metal ball attached by a steel wire to a grip — forces the athlete to wobble around the center of rotation. Over geological time, the gravitational pull of Sun and Moon, growing or shrinking ice sheets and the slow drift of the continents will move mass around and cause Earth's poles to shift, but human activity can cause significant changes on a much smaller timescale. 'As we trap water behind dams, not only does it remove water from the oceans, thus leading to a global sea level fall, it also distributes mass in a different way around the world,' says Natasha Valencic, a graduate student in Earth and planetary sciences at Harvard University and lead author of a new study. Valencic and her colleagues used a global database of dams to map the locations of each dam and the amount of water each impounds, comparing their construction history with recorded shifts of Earth's poles. From 1835 to 1954, many dams were built in North America and Europe, shifting these areas toward the equator. The North Pole moved 20.5 centimeters (8 inches) toward the 103rd meridian east, which passes through Russia, Mongolia, China, and the Indochina Peninsula. Then, from 1954 to 2011, dams were built in East Africa and Asia, and the pole shifted 57 centimeters (22 inches) toward the 117th meridian west, which passes through western North America and the South Pacific. Over the entire period from 1835 to 2011, the poles moved about 113 centimeters (3.7 feet), with about 104 centimeters (3.4 feet) of movement happening in the 20th century. Already in 2023, Seo et al. published a similar study in the journal Geophysical Research Letters focusing on groundwater use. By pumping water out of the ground and moving it elsewhere, humans have shifted such a large mass of water that the Earth tilted nearly 80 centimeters (31.5 inches) east between 1993 and 2010 alone. The melting of glaciers and ice caps due to climate change, resulting in a mass shift from the poles to the equator, is expected to amplify this effect further, as a study published in the journal Science Advances suggested as early as 2016. Observed polar motion (red arrow labelled 'OBS') due to water/groundwater mass redistribution Earth's poles normally change by several meters within a year due to the planet's natural wobbling, so the observed changes don't run the risk of catastrophic consequences. However, such studies highlight how profoundly human activity can influence the entire planet. The study,"True Polar Wander Driven by Artificial Water Impoundment: 1835–2011," was published in the journal Geophysical Research Letters. Additional material provided by Samson Reiny for the American Geophysical Union.
Gizmodo
13-07-2025
- Science
- Gizmodo
Human-Constructed Dams Have Shifted the Earth's Poles, Scientists Say
Humans have built so many dams around the world that the Earth's poles have wandered away from the planet's rotational axis, new research suggests. Over the last 200 years, humans have constructed nearly 7,000 massive dams, impounding enough water to nudge the Earth's poles by about three feet (one meter) and cause a 0.83-inch (21-millimeter) drop in global sea levels, according to a new study in Geophysical Research Letters. This drift is possible because Earth's solid crust forms a hard shell around a molten layer of gooey magma. This means that whenever a significant amount of mass is redistributed across the planet's surface, the outermost rock layer wobbles, shifting relative to Earth's molten interior. When this happens, different areas on the Earth's surface end up directly over the planet's rotational axis. As a result, the planet's poles pass through different surface locations than before, a phenomenon known as true polar wander. 'As we trap water behind dams, not only does it remove water from the oceans—thus leading to a global sea level fall—it also redistributes mass around the world,' Natasha Valencic, a graduate student at Harvard University and lead author of the new study, said in a statement. In the study, Valencic and her team analyzed a previously published global database of dams to figure out their locations, the volume of water they store, and how that stored water has impacted Earth's mass distribution. Previously, the database revealed that 6,862 large dams built between 1835 and 2011 contributed to a decrease in sea levels. Collectively, these dams hold enough water to fill the Grand Canyon twice. The results showed that global dam-building has caused Earth's poles to shift in two phases. The first phase, from 1835 to 1954, coincided with a boom in dam construction in North America and Europe. These areas shifted toward the equator, and as a result, the North Pole moved about 8 inches (25 centimeters) toward the 103rd meridian east, a line that passes through Russia, Mongolia, and China. During the second wave of dam construction, between 1954 and 2011, most dams were built in Asia and East Africa. As a result, the North Pole shifted 22 inches (57 centimeters) toward the 117th meridian west, which passes through western South America and the South Pacific. Polar wander is not linear; instead, it follows a wobbly path, which is why the total shift does not add up precisely to 3.7 feet. While the results are relatively subtle, they highlight the need for researchers to account for water stored in dams when predicting future sea level rise. In the 20th century, global sea levels rose 4.7 to 6.7 inches (12 to 17 centimeters), but humans trapped about a quarter of that volume behind dams, according to Valencic. 'Depending on where you place dams and reservoirs, the geometry of sea level rise will change,' she said. 'That's another factor we need to consider, because these changes can be quite large and significant.'
