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During the last century, the axis of rotation of the Earth has drifted about ten meters. We know, from the records of the relative motions of the stars, that this change has been going on for at least thousands of years. Now, scientists have identified three main factors that also drive this effect – and human activity is one of them.
The Earth is not a perfect sphere, but rather an oblate spheroid – crushed from above, so that the diameter from one pole to the other is less than the diameter around the l '. equator. The planet also has non-uniform geological features, with parts of the world covered by vast oceans, while others are carved out of high mountains. Naturally, this causes weight imbalances on the surface of the Earth, which explains why the axis of rotation of the Earth moves over time by 10.5 cm each year, judging from measurements taken in the 20th century. century.
Scientists thought that glacier rebound or isostatic rebound was responsible for much of the planet's oscillation. As the glaciers recede, the soil below – suddenly free of all this icy mass – reacts like a rising bread dough. This is a slow process, in progress since the end of the last ice 16,000 years ago, when most of the northern hemisphere was covered by glaciers.
However, researchers at NASA's Jet Propulsion Laboratory have found that glacier bounce is responsible for only one-third of the oscillation of the axis per year. The team provided data on changes in terrestrial ice and ocean water during the 20th century in a computer model of the Earth's spin. Other important factors taken into account include human activities such as the depletion of groundwater or the construction of artificial reservoirs.
The results suggest that the melting of the Greenland icecap is responsible for only 3.5 centimeters of the displacement of the Earth's axis. NASA estimates that 7,500 gigatonnes of Greenland ice melted in the ocean in the 20th century. Because the ice layer melted mainly because of greenhouse gases released into the atmosphere, this effect was directly related to human activity.
Finally, convection inside the mantle is responsible for another third of the axial shift. The mantle of the planet is constantly moving, with warmer materials near the heart rising upward while colder materials near the surface sink. This vertical movement cycle is also responsible for plate tectonics, vulcanism or earthquakes.
NASA researchers say that the oscillation of the Earth is not dangerous. No calamity should result and the climate would not be affected. The results, however, are important for scientists, especially those studying climate, as they inform where the most important mass transport is currently occurring. The study also adds to a body of evidence showing how man is an important force capable of modifying even the spin of the planet.
For more information, visit NASA's interactive polar motion simulation.
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