VOA 慢速：抽取地下水改变了地球的运转方式
Study: Pumping Groundwater Has Changed How Earth Turns
刘立军 供稿
TRANSCRIPT
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 tilt 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 rotation 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 rotational axis 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 tilted nearly 80 centimeters towards the 64 degrees east longitude 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 noted 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 affected 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.”
I’m Bryan Lynn.
VOCABULARY
1. tilt n. a position in which one end or side of sth is higher than the other; an act of tilting sth to one side 倾斜；倾侧。例如：The table is at a slight tilt. 这桌子有点儿歪。
2. gigaton n. 十亿吨;
3. millimeter n. 毫米
4. the earth’s crust 地壳
QUESTIONS
Listen to the news and choose the best answer to each question you hear.
1. What is the main finding of the recent study on polar motion?
A) Groundwater pumping affects Earth’s rotation and sea level rise.
B) The rotational pole changes caused by groundwater are too small to affect Earth’s seasons.
C) The Earth tilted nearly 80 centimeters towards the 64 degrees east longitude line.
D) Water movements on Earth can cause the planet to rotate differently.
2. Which areas experienced the biggest changes in polar motion during the study period?
A) Western North America and Northwestern India.
B) Western North America and Southeast Asia.
C) Eastern Europe and South America.
D) Western Europe and Northeast Asia.
3. What did the 2016 study by Surendra Adhikari focus on?
A) The effects of water redistribution on polar motion.
B) The impact of groundwater pumping on sea level rise.
C) The relationship between ocean currents and Earth’s rotation.
D) The role of climate change in Earth’s tilt.
4. According to the study, can changes in slowing the rate of groundwater removal affect Earth’s polar motion?
A) Yes, but only if efforts are highly organized and continued for many years.
B) No, the rotational pole changes caused by groundwater are too small.
C) Yes, any changes in groundwater removal will significantly impact polar motion.
D) No, the study found no correlation between groundwater removal and polar motion.
5. What did the recent study suggest about the impact of groundwater pumping on sea level rise?
A) Groundwater pumping has no impact on sea level rise.
B) Groundwater pumping is a major contributor to sea level rise.
C) Groundwater pumping affects sea level rise, but to a smaller extent.
D) The study did not focus on the impact of groundwater pumping on sea level rise.
6. What did the researchers use to estimate the amount of groundwater pumped to the Earth’s surface?
A) Data collected by satellites over nearly 20 years.
B) Climate computer models and weather forecasts.
C) Observations from ground-based sensors and instruments.
D) Historical records of groundwater extraction in different regions.
KEY
1. What is the main finding of the recent study on polar motion?
A) Groundwater pumping affects Earth’s rotation and sea level rise.
B) The rotational pole changes caused by groundwater are too small to affect Earth’s seasons.
C) The Earth tilted nearly 80 centimeters towards the 64 degrees east longitude line.
D) Water movements on Earth can cause the planet to rotate differently.
【答案】C
【解析】细节题。根据文章，研究小组的主要发现是，在1993年到2010年期间，地球向东经64度线倾斜了近80厘米。
2. Which areas experienced the biggest changes in polar motion during the study period?
A) Western North America and Northwestern India.
B) Western North America and Southeast Asia.
C) Eastern Europe and South America.
D) Western Europe and Northeast Asia.
【答案】A
【解析】细节题。根据文章的最后一段，研究指出，研究期间在中纬度地区记录到了最大的变化，而西北美洲和印度西北部是大部分水资源重新分配的地区。
3. What did the 2016 study by Surendra Adhikari focus on?
A) The effects of water redistribution on polar motion.
B) The impact of groundwater pumping on sea level rise.
C) The relationship between ocean currents and Earth’s rotation.
D) The role of climate change in Earth’s tilt.
【答案】A
【解析】细节题。根据文章，Surendra Adhikari在2016年发表的研究专注于水重新分配对地级移动的影响。
4. According to the study, can changes in slowing the rate of groundwater removal affect Earth’s polar motion?
A) Yes, but only if efforts are highly organized and continued for many years.
B) No, the rotational pole changes caused by groundwater are too small.
C) Yes, any changes in groundwater removal will significantly impact polar motion.
D) No, the study found no correlation between groundwater removal and polar motion.
【答案】A
【解析】推理题。根据文章，研究指出，理论上来说，减缓地下水开采速度可能会对地球的极移产生影响，但只有在这一行动具有高度组织性并持续多年的情况下才能看到显著的变化。
5. What did the recent study suggest about the impact of groundwater pumping on sea level rise?
A) Groundwater pumping has no impact on sea level rise.
B) Groundwater pumping is a major contributor to sea level rise.
C) Groundwater pumping affects sea level rise, but to a smaller extent.
D) The study did not focus on the impact of groundwater pumping on sea level rise.
【答案】C
【解析】细节题。根据文章，最近的研究表明，地下水向海洋的流动在某种程度上影响了地球的旋转，并可能导致海平面上升。
6. What did the researchers use to estimate the amount of groundwater pumped to the Earth’s surface?
A) Data collected by satellites over nearly 20 years.
B) Climate computer models and weather forecasts.
C) Observations from ground-based sensors and instruments.
D) Historical records of groundwater extraction in different regions.
【答案】A
【解析】细节题。根据文章，研究人员依靠卫星收集的近20年的数据来估算抽取到地球表面的地下水量。
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