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Humans are responsible for some of the oscillations of Earth's rotation.
Since 1899, the axis of rotation of the Earth has moved about 10.5 meters. Now, the research quantifies the reasons and finds that a third is due to melting ice and rising sea levels, especially in Greenland – which places blame on anthropogenic climate change .
Another third of the flicker is due to the fact that the land masses are expanding as glaciers retreat and lighten their load. The last part is the fault of the slow chipping of the mantle, the viscous middle layer of the planet.
"We have provided evidence of several unique processes that are the essential driver of the Earth's changing axis," said Surendra Adhikari, Earth System Scientist at the Jet Propulsion Laboratory in Pasadena, California. [Why Does the Earth Rotate?]
Wobble Earth
Scientists have long known that the distribution of mass around the Earth determines its spin, much like the distribution of the shape and weight of a spinning top. Erik Ivins, co-author of the study and principal investigator, also said that the spin of the Earth is not perfectly equal, as scientists know, thanks to slight stirrings in the movements of the stars in the night sky. at JPL. Since the 1990s, spatial measurements have also confirmed that the axis of rotation of the Earth derives from a few centimeters a year, usually to Hudson Bay, in northeastern Canada.
The researchers knew that part of this oscillation was due to a glacial isostatic adjustment, a process that has been ongoing since the end of the last ice age, 16,000 years ago. As the glaciers recede, they relieve the ground beneath their mass. Gradually, over thousands of years, the earth responds to this relief by rising like bread dough. (In some places on the edges of the old ice caps, the earth could also collapse because the ice forced it to inflate upwards.)
But in the new research, published in the November issue of Earth and Planetary Science Letters, Adhikari and his colleagues found that glacier isostatic adjustment was responsible for only about 3.5 inches of axis per year. year. It was only about a third of the flicker – 10.5 cm (4 inches) – observed every year during the 20th century.
To fill this gap, the research team developed a computer model of Earth's spin physics, providing data on changes in the equilibrium of ice and terrestrial ocean waters during the twentieth century. The researchers also took into account other changes in the land and in the water, such as the depletion of groundwater and the construction of artificial reservoirs, all of which are part of the terraforming of the earth. On the planet. [What in the World Would Happen If Earth Were to Spin Backward?]
The results revealed that these environmental processes cause another oscillation of 1.7 inches (4.3 cm) each year. The melting of the Greenland icecap was a particularly important factor, according to the researchers. "It's because Greenland has released a large amount of water that was once locked in the oceans, where its mass has been redistributed," Ivins told Live Science. Mountain glaciers and small ice caps have also contributed to sea level rise, he added; but they are not so concentrated and their effects on the rotation of the Earth often cancel.
Basic considerations
Glaciers and ice melting still left a third of the flicker, so Adhikari and his team turned to the interior. The mantle of the Earth is not static, he says, but moves by convection: a warmer material, closer to the heart, rises and a cooler material sinks into a cycle of motion vertical. By including convection in the Earth's oscillation model, researchers accounted for the last third of changes in rotation during the 20th century.
It is important to understand that this swing is not the prelude to an environmental disaster, said Ivins and Adhikari. This does not affect agriculture or the climate per se, and it is easy to correct any small impact on the navigation equipment.
"The amount [of drift] it's not huge, "Adhikari said.
But it gives scientists a way to determine where the earth's mass is and where it's going. For example, according to Adhikari, the melting of Greenland has become an increasingly important factor in changing the location of the axes over the last 15 years, pushing the drift towards the east.
"This fact is important for climatologists," said Ivins, "because they can understand, in the broadest sense of the term, what are the most important mass transports taking place today."
The JPL website hosts a simulation of the polar wobble and its contributing factors.
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