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NASA study uncovers three factors responsible for Earth's irregular spin

NASA study uncovers three fact...
A NASA study has found three main factors contributed to a shift in the Earth's axis over the 20th century
A NASA study has found three main factors contributed to a shift in the Earth's axis over the 20th century
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The light blue line indicates the direction of the tilt of the Earth's axis over the 20th century. The pink line represents the total influence of the three main factors: Greenland ice loss (blue), glacial rebound (orange) and mantle convection (red)
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The light blue line indicates the direction of the tilt of the Earth's axis over the 20th century. The pink line represents the total influence of the three main factors: Greenland ice loss (blue), glacial rebound (orange) and mantle convection (red)
A NASA study has found three main factors contributed to a shift in the Earth's axis over the 20th century
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A NASA study has found three main factors contributed to a shift in the Earth's axis over the 20th century

The Earth's spin isn't as consistent as it may seem. In fact, it naturally drifts and wobbles on its axis over time, and that's generally chalked up to the way mass is distributed and redistributed across the planet's surface. Now, NASA scientists studying data gathered across the entire 20th century have identified three broad processes that play a part.

According to previous research, between 1900 and 2000 the Earth's spin axis drifted about 4 in (10 cm) every year, adding up to a total shift of more than 33 ft (10 m) by the end of the century. Traditionally, the main culprit for this kind of wobble is thought to be glacial rebound. During ice ages, glaciers form and their weight presses down on the Earth's crust. Later, as those glaciers melt – as is happening today at pretty alarming speeds – the rock below begins to rise up again, redistributing the Earth's mass and affecting its rotation.

But when the NASA researchers conducted a statistical analysis of that 20th century data, they found that glacial rebound only accounts for around a third of the observed axial wobble.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis," says Surendra Adhikari, first author of the study. "But recently, many researchers have speculated that other processes could have potentially large effects on it as well. We assembled models for a suite of processes that are thought to be important for driving the motion of the spin axis. We identified not one but three sets of processes that are crucial – and melting of the global cryosphere (especially Greenland) over the course of the 20th century is one of them."

The drastic climate shift we've seen over the last century has reduced glacial ice pretty much everywhere, but Greenland has been particularly hard-hit, losing about 7,500 gigatons of ice. That affects the Earth's spin not only by redistributing mass into the oceans, but because of its location on the globe.

"There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole – which Greenland is – or from the South Pole (like Patagonian glaciers), it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole," says Eric Ivins, co-author of the study.

According to the study, the third major contributor to the wobble is mantle convection, referring to the movements of the molten rock deep inside the Earth. Not only is this kind of motion responsible for the movements of the tectonic plates, but the rise and fall of material in the mantle can redistribute mass and, as a result, affect the planet's spin.

Having identified these three key factors, the researchers say future work can do a better job of separating effects caused by longer-term Earth processes from effects caused by climate change. Of course, they are still linked too, and the team says that continued warming could accelerate the loss of ice in Greenland, which in turn could accelerate the rate of the planet's spin axis shift.

The research was published in the journal Earth and Planetary Science Letters.

Source: NASA/JPL

6 comments
Wastewater Al
Every day thousands of tons of coal get moved from newcastle Australia to the northern hemisphere that's been happening for 80 to 100 years that must have an effect on something Least of all the size of the land mass in Australia perhaps not gigatons but at least
Subtle
Take an ordinary top that children play with. Spin it and even the most perfectly balanced one will precess. It is due to torque and the Earth's spin has been precessing since Day One. As to the rate of ice melt. That maximized some 8,000 to 6,000 years ago with the rapid warming called the Holocene Optimum. Lately, the melt as shown by the slow increase in sea levels has been very slow.
Gregg Eshelman
What are the minimum and maximum latitudes the Arctic and Antarctic circles move to, at the theoretical minimum and maximum of Earth's axial tilt?
How much surface area is between those bounds? How much farther north and south did the circles shift during the 20th century? How much surface area in the stripes between the 1900 latitudes and 2000 latitudes? How about a plot of the number of daylight hours in 1 degree latitude steps each year for the 20th century, from the 1900 circles' latitude to the poles?
Those are some numbers that are important to the overall climate on Earth, yet I've not found anyone who wants to bother with calculating the effect - especially not anyone who is determined to prove it's all due to what humans do.
Since Earth's axis has been on the trend towards its minimum tilt, that's had to have had a moderating effect on the climate. As less and less area at the poles spends less time each year in continuous dark, there's less time to build up snow and ice, and less area to do it.
Another thing that should be accounted for in climate models is that in winter the Arctic can get heat from both water and air convection. The Arctic, except for some narrow slivers around parts of the coast of Antarctica, gets no heat from water convection during the 24 hour a day darkness period of winter.
a.l.
“The drastic climate shift we've seen over the last century has reduced glacial ice pretty much everywhere, but Greenland has been particularly hard-hit, losing about 7,500 gigatons of ice. That affects the Earth's spin not only by redistributing mass into the oceans, but because of its location on the globe.”
This misses one major factor: most glacial ice is locked up at higher latitudes. When it melts it not only nly flows into the ocean but, due to centrifugal force from Earth’s rotation, the mass of all that water mass migrates to the equitorial regions where the planet’s rotation is fastest. In theory, an increase of mass at the equator should eventually reduce precession at the poles, not exacerbate it.
rude.dawg
Climate shift affecting the rate of the planet's spin axis shift? Or is it the other way around? https://newatlas.com/earth-orbit-climate-change/54539/
Stephen Smith
Some of you also forget France, USA, Soviet Union, etc. were involved in nuclear bomb tests and there's also the 2 atom bombs dropped on Japan during second world war to account for and how they can have a large effect on the axis and rotational movement of the earth, but that ugly subject hasn't been brought up or accounted for as a factor or an added factor.