Around the millennium’s turn, the Earth’s spin began to deviate, and no one knew why.
For decades, scientists have been tracking the average location of our planet’s rotating axis, the imaginary rod around which it revolves, as it gradually moves south, away from the physical North Pole and toward Canada. But then it took an abrupt turn and began traveling east.
Researchers eventually came to a stunning discovery about what had occurred. Accelerated melting of the polar ice sheets and mountain glaciers had altered the distribution of mass around the globe sufficiently to impact its rotation.
Now, some of the same scientists have discovered another element that has had a similar effect: massive amounts of water pumped out of the earth for crops and residences.
“Wow,” Ki-Weon Seo, who conducted the study that led to the new finding, remembers thinking when his calculations revealed a close correlation between groundwater extraction and Earth’s axis shifting. It came as a “big surprise,” according to Seo, a geophysicist at Seoul National University.
Water experts have long warned of the dangers of excessive groundwater consumption, especially when water from underground aquifers becomes an increasingly important resource in drought-stricken places such as the American West. When water is pumped out of the ground but not refilled, the land can sink, causing damage to buildings and infrastructure as well as reducing the amount of subterranean space available to store water in the future.
According to experts, global groundwater depletion more than quadrupled between 1960 and 2000, reaching around 75 trillion gallons per year. Satellites that detect shifts in Earth’s gravity have now shown the startling amount to which groundwater supplies have plummeted in specific locations, notably India and California’s Central Valley.
“I’m not surprised that it would have an effect” on Earth’s rotation, said Matthew Rodell, a NASA Goddard Space Flight Center earth scientist. “It’s impressive they were able to tease that out of the data,” Rodell said, referring to the new study’s authors, who published their findings this month in the journal Geophysical Research Letters. “And that the observations they have of polar motion are precise enough to see that effect.”
