By pumping water out of the ground and transporting it elsewhere, humans shifted such a large mass of water that the Earth tilted nearly 80 cm (31.5 in) east between 1993 and 2010 alone, according to a new study published in the journal Geophysical Research Letters.
Based on climate models and scientists previously estimated Humans pumped 2,150 gigatonnes of groundwater, equivalent to more than 6 millimeters (0.24 in) of sea level rise, from 1993 to 2010. But validating this estimate is difficult.
One approach lies at the Earth’s rotational pole, which is the point around which the planet orbits. It moves through a process called polar motion, which is when the position of the Earth’s rotational pole changes relative to the crust. The distribution of water on the planet affects how the mass is distributed. Like adding a little weight to a spinning top, the Earth spins a little differently as it moves water.
“Earth’s rotation pole changes often,” said Ki-wyun Seo, a geophysicist at Seoul National University who led the study. “Our study shows that among climate-related causes, groundwater redistribution actually has the greatest impact on shaft drift.”
It was the ability of water to change the Earth’s rotation Discovered in 2016To date, the specific contribution of groundwater to these circulation changes has not been explored. In the new study, the researchers modeled the observed changes in Earth’s rotational pole drift and water movement—first, taking into account only ice sheets and glaciers, and then adding different scenarios for groundwater redistribution.
The model only matched the polar drift observed once the researchers included 2,150 gigatonnes of groundwater redistribution. Without it, the model was stopped at 78.5 cm (31 in), or 4.3 cm (1.7 in), of drift annually.
“I am very happy to find the unexplained cause of shaft drift,” Seo said. “On the other hand, as a land-dweller and parent, I am concerned and surprised to see that groundwater pumping is another source of sea level rise.”
“This is an amazing contribution and definitely an important documentation,” said Surendra Adhikari, a research scientist at JPL who was not involved in this study. Adhikari published a 2016 paper on water redistribution affecting rotational drift. “They’ve identified the role of groundwater pumping in polar motion, and it’s very important.”
The location of groundwater is important to the extent to which it can alter polar drift; Redistribution of water from mid-latitudes has a greater effect on the shaft. During the study period, most of the water was redistributed in western North America and northwest India, both at midlatitudes.
Seo said states’ attempts to slow groundwater depletion rates, especially in those sensitive areas, could theoretically reverse the change in erosion, but only if such conservation methods persist for decades.
The shaft usually changes by several meters in about a year, so changes caused by groundwater pumping are not at risk of changing seasons. But on geological time scales, polar drift can have an impact on climate, Adhikari said.
The next step for this research may be to look back.
“Observing changes in Earth’s rotational pole is useful for understanding continent-wide differences in water storage,” Seo said. “Polar motion data has been available since the late 19th century. So, we can use this data to understand the differences in continental water storage over the past 100 years. Were there any changes in the hydrological regime caused by a warming climate? Polar motion can hold the answer.” .
more information:
Ki‐Weon Seo et al, Earth’s pole drift confirms groundwater depletion as an important contributor to global sea level rise 1993–2010, Geophysical Research Letters (2023). doi: 10.1029/2023GL103509
This story is republished with permission from Eos, and hosted by the American Geophysical Union. Read the original storyhere.