By Rowenna Hoskin | Science Editor
Earth’s north and south poles are the point where its axis of rotation intersects the surface, but it is not fixed. The axis is caused by the changes in how the Earth’s mass is distributed, which consequently causes the poles to move.
In the past, the only natural factors like ocean currents and the convection of hot rock in the Earth’s core effected the drifting position of the poles. According to new research, the loss of billions of tonnes of ice a year into the oceans resulting from climate change has caused the poles to move in new directions since the 1990s.
In 1995, scientists found that the direction of polar drift changed from southward to eastward and that the average speed of drift from 1995 to 2020 was 17 times faster than from 1981 to 1995.
Since 1980, the poles’ position has shifted around 4 metres in distance.
“The accelerated decline [in water stored on land] resulting from glacial ice melting is the main driver of the rapid polar drift after the 1990s,” concluded the team, led by Shanshan Deng, from the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Science.
Gravity data from the Grace satellite, launched in 2002, had been used to link glacial melting to pole movements in 2005 and 2012, following an increase in ice loss. Deng’s research breaks new ground as it links to before the satellite was launched; it shows that human activities have been shifting the poles since the 1990s.
The research showed that most of this shift was due to glacial losses, but Deng’s research suggests that the pumping up of groundwater may have also contributed.
Groundwater is stored beneath the land but humans pump it up for drinking water and agriculture. After this, most of it flows out to sea, redistributing its weight around the world. In the past 50 years, humanity has removed 18tn tonnes of water from underground reservoirs without it being replaced.
Vincent Humphrey, from the University of Zurich who was not involved in the research, says that the new study demonstrates the effect human activities have had on the redistribution of huge amounts of water around the planet: “It tells you how strong this mass change is –it’s so big that it can change the axis of the Earth.” This movement is not large enough to affect daily life, but it could change the length of a day – even if it is only by milliseconds.
Some scientists argue that the scale of this impact means that the Anthropocene, a new ecological epoch – must be declared. Human activity has physically altered not only the life and landscape of the planet, but the physics of the planet itself.