VOA科学技术2023--Study: Pumping Groundwater Has Changed How Earth Turns

Study: Pumping Groundwater Has Changed How Earth Turns

A recent study says that pumping massive amounts of groundwater to the surface can affect the position of Earth's poles.

The poles are at either end of the imaginary line running through the Earth. The turning motion of Earth around this line causes day and night. The tilt¹ of the line, in relation to the sun, causes the seasons.

Scientists have known for more than 100 years that the Earth's poles change position a little over time with what is called polar motion.

A group of international scientists recently published their study of polar motion. Earlier studies linked the way water is spread out over the Earth to polar motion. The scientists wanted to see if the movement of groundwater could help explain differences between observed and predicted polar motion.

The researchers used a climate computer model to estimate that humans pumped a total of 2,150 gigatons of groundwater to the Earth's surface from 1993 to 2010. One gigaton is equal to about 1 billion metric tons, the American space agency NASA notes. The model estimated that world sea levels rose six millimeters because of the additional groundwater.

Groundwater pumped to the surface is used for crops and drinking water. It is an important resource to support human life. The recent study suggests that the movement of groundwater to the oceans can, in a way, affect Earth's rotation² and might also add to sea level rise.

A 2016 study first showed evidence that ocean water flows can affect polar motion. But the latest study is the first to explore in depth how groundwater brought to the surface might change Earth's tilt.

The researchers created their climate model to study polar motion. Described another way, polar motion is when the position of the planet's rotational³ axis⁴ moves in relation to Earth's crust.

Water movements on Earth can cause the planet to rotate "a little differently as water is moved around," the researchers said in a statement.

Ki-Weon Seo is a geophysicist at Seoul National University who led the study. It recently appeared in the publication Geophysical Research Letters.

Seo said, "Earth's rotational pole actually changes a lot." He added that the study shows "that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole."

The researchers depended on data collected by satellites over nearly 20 years. They used their computer model to estimate what kinds of water redistribution caused a notable change in the Earth's tilt. The team's main finding was that the Earth tilted⁵ nearly 80 centimeters towards the 64 degrees east longitude⁶ line between 1993 and 2010.

The study notes that where the groundwater is pumped from affects how much polar motion happens. The biggest changes were recorded in mid-latitude areas: areas not too close to the North Pole and not too near the equator. During the study period, the most water was redistributed in western North America and northwestern India. Both of these are in mid-latitude areas.

Seo noted⁷ that the rotational pole changes caused by groundwater are too small to affect Earth's seasons. He said that, in theory, making changes to slow the rate of groundwater removal could affect Earth's polar motion. But major changes would likely only be seen if such efforts were highly organized and continued for many years.

"I'm very glad to find the unexplained cause of the rotation pole drift," Seo said. "On the other hand, as a resident of Earth and a father, I'm concerned and surprised to see that pumping groundwater is another source of sea-level rise."

Seo noted that the latest study could mark the start of additional research into how water flow changes affected⁸ different, specific areas of the world. He said the same rotational pole data could be used to learn about possible causes of redistributed water over the past 100 years. "Were there any...changes resulting from the warming climate? Polar motion could hold the answer," he added.

Surendra Adhikari is a research scientist at NASA's Jet Propulsion Laboratory. He was not involved in this study. In a statement, Adhikari said the research was "a nice contribution and an important documentation for sure."

He published the 2016 paper on water redistribution's effects on rotational drift. Adhikari added that the study clearly demonstrates "the role of groundwater pumping on polar motion, and it's pretty significant."

Words in This Story

tilt – n. a state of having one side higher than the other; leaning to one side

rotation – n. the act of turning around a central point

axis –n. a line around which something turns, such as the Earth

crust – n. the outer, solid part of the Earth

redistribute – v. to take from one area and put in another area

impact – n. effect

longitude –n. the system of lines going north to south that help travelers know where they are on the Earth

drift –n. the slow movement of something away from where it was before to a new position that is hard to predict

contribute – v. to help cause something to happen

role – n. the part something plays in an event or situation

1 tilt   

v.(使)倾侧；(使)倾斜；n.倾侧；倾斜

参考例句：

• She wore her hat at a tilt over her left eye.她歪戴着帽子遮住左眼。
• The table is at a slight tilt.这张桌子没放平，有点儿歪.

2 rotation   

n.旋转；循环，轮流

参考例句：

• Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
• The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。

3 rotational   

adj.回转的，轮流的

参考例句：

• A synchronous motor drives the measuring bob at a constant rotational speed.同步马达驱动测锤以恒速旋转。
• With some limitations,this is true also of rotational degrees of freedom.在某些限定条件下，这一说法对转动自由度也成立。

4 axis   

n.轴，轴线，中心线；坐标轴，基准线

参考例句：

• The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
• The axis of a circle is its diameter.圆的轴线是其直径。

5 tilted   

v. 倾斜的

参考例句：

• Suddenly the boat tilted to one side. 小船突然倾向一侧。
• She tilted her chin at him defiantly. 她向他翘起下巴表示挑衅。

6 longitude   

n.经线，经度

参考例句：

• The city is at longitude 21°east.这个城市位于东经21度。
• He noted the latitude and longitude,then made a mark on the admiralty chart.他记下纬度和经度，然后在航海图上做了个标记。

7 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

8 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。