Earth’s rotation wobbles. NASA says humans partly to blame.

NASA scientists have discovered three factors that influence Earth's rotational wobble. Thankfully, while the Earth may wobble, it won't fall down.

  • Despite what your classroom globe taught you, Earth is neither a perfect sphere nor does it rotate resolutely along its axis.
  • Scientists originally thought glacial rebound was responsible for Earth's polar motion, but a new study argues that mantle convection and contemporary ice mass loss share the blame.
  • The study's authors note that this new understanding of axial spin provides another link between ice melt and rising sea levels, allowing us to more accurately model global climate change.

Picture Earth in your mind. Chances are what you're imagining is a blue marble gracefully pirouetting through space on its axis. It's a model we've grown accustomed to by way of movies and classroom globes. It's hardly a realistic representation, though.

While the Earth is round, it's not a perfect sphere but rather an oblate spheroid mass. It also doesn't rotate along a resolutely straight spin axis. Instead, it drifts, wobbles, and tilts along its orbit like a solar partygoer, one who's just on the fun side of squiffy.

Scientists have long known that the Earth wobbles on its spin axis, but a new study has shown that the Earth's drift has increased over the last century and identifies three major causes: glacial rebound, mantel convection, and the melting of ice mass.

And wouldn't you know it? We're partially to blame for that last one.

Glacial rebound

The light blue line represents the observed direction of polar motion\u200b. The pink line is the sum of the influences of glacial rebound (yellow), mantle convection (red), and Greeland ice loss (blue) on Earth's rotation.

Photo by NASA/JPL-Caltech

The light blue line represents the observed direction of polar motion. The pink line is the sum of the influences of glacial rebound (yellow), mantle convection (red), and Greeland ice loss (blue) on Earth's rotation.

The paper, titled What Drives 20th Century Polar Motion?, was published in Earth and Planetary Science Letters and brought together scientists from NASA's Jet Propulsion Laboratory (JPL), the German Research Centre for Geosciences, the Geological Survey of Denmark and Greenland, and other organizations.

The study looked at observational and model-based data from the 20th century to determine what caused the increased wobble or, more technically, polar motion.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis. But recently, many researchers have speculated that other processes could have potentially large effects on it as well," Surendra Adhikari, the study's first author and an earth scientist at JPL, said in a press release.

The study found glacial rebound an important factor in explaining Earth's rotational wobble. According to the release, heavy glaciers depressed Earth's surface during the last ice age, their weight pushing the land deeper into the surface. As the ice melts, the land rises back to its original position. Think of it as memory foam on the geologic scale. Like the memory foam, Earth's mass redistributes itself and this causes changes in the planet's rotation.

Digging deeper

However, the researchers found that glacial rebound is only one of three important factors. The second is mantle convection, a geophysical process that involves the planet's core heating up the mantle. Convection currents carry the hotter, less dense liquid rock up from the lower mantle, while dragging the denser rock of upper mantle and lithosphere back down. This constant flow of geologic material is driving force of plate tectonics, volcanic activity, seafloor spreading, and so on.

Like glacial rebound, mantle convection moves and redistributes Earth's mass, thus affecting its rotation.

The glacial motion into the ocean

\u200bRink Glacier in western Greenland forms a meltwater lake in its center.

Photo by NASA/OIB

Rink Glacier in western Greenland forms a meltwater lake in its center.

This is where we come in. The researchers argue that there is another factor greatly influencing Earth's polar motion and its contemporary drift. What is it? The 20th-century reduction of the global cryosphere. In particular, Greenland's ice melt is having the largest impact due its location on the planet.

Erik Ivins, co-author and senior research scientist at JPL, explains: "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."

As temperatures have increased throughout the 20th century, Greenland's ice mass has diminished significantly. As the press release notes, about 7,500 gigatons of Greenland's ice melt — a weight of more than 20 million Empire State Buildings — has found its way into our oceans. As this ice mass continues to melt and diffuse across the planet, it will further affect the drift of Earth's spin not to mention sea levels.

These three main factors — glacial rebound, mantle convection, and ice melt — have altered the planet's spin axis. But by how much? In total, the paper shows that Earth's rotation drifts about 10 centimeters per year. During the 20th century, this resulted in a shift of about 10 meters.

Writing for Forbes, geologist Trevor Nace points out that this difference isn't significant enough to effect ecosystems, and we can account for any navigational impacts it may have with modern technology.

Earth's rotational wobble won't bring about an extinction event, but understanding its cause is nonetheless important. This research gives us further insight into how human activity can alter the planet on a global scale. While we tend to talk about throwing the planet off balance, this time it is literally true.

America’s education system is centuries old. Can we build something better?

The Lumina Foundation lays out steps for increasing access to quality post-secondary education credentials.

Sponsored by Lumina Foundation
  • America's post-high school education landscape was not created with the modern student in mind. Today, clear and flexible pathways are necessary to help individuals access education that can help them lead a better life.
  • Elizabeth Garlow explains the Lumina Foundation's strategy to create a post-secondary education system that works for all students. This includes credential recognition, affordability, a more competency-based system, and quality assurance.
  • Systemic historic factors have contributed to inequality in the education system. Lumina aims to close those gaps in educational attainment.
  • In 2019, Lumina Foundation and Big Think teamed up to create the Lumina Prize, a search to find the most innovative and scalable ideas in post-secondary education. You can see the winners of the Lumina Prize here – congratulations to PeerForward and Greater Commons!

First solar roadway in France turned out to be a 'total disaster'

French newspapers report that the trial hasn't lived up to expectations.

Image source: Charly Triballeau / AFP / Getty Images
Technology & Innovation
  • The French government initially invested in a rural solar roadway in 2016.
  • French newspapers report that the trial hasn't lived up to expectations.
  • Solar panel "paved" roadways are proving to be inefficient and too expensive.
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What was it like to live in a Japanese concentration camp?

During World War II, the U.S. incarcerated over 100,000 Japanese Americans in concentration camps throughout the West.

Universal History Archive/Universal Images Group via Getty Images
Politics & Current Affairs
  • Now that the issue of concentration camps in the U.S. has once again reared its head, it can be beneficial to recall the last time such camps were employed in the U.S.
  • After Pearl Harbor, the U.S. incarcerated over 100,000 Japanese Americans in camps, ostensibly for national security purposes.
  • In truth, the incarceration was primarily motivated by racism. What was life like in the U.S.'s concentration camps?

On February 19, 1942, President Roosevelt issued Executive Order 9066, which authorized and directed military commanders "to prescribe military areas … from which any or all persons may be excluded, and with respect to which, the right of any person to enter, remain in, or leave shall be subject to whatever restrictions the Secretary of War or the appropriate Military Commander may impose in his discretion." Under the authority of this executive order, roughly 112,000 men, women, and children of Japanese descent — nearly two-thirds of which were American citizens — were detained in concentration camps.

How did the camps get their start?

With the benefit of a nearly 80-year perspective, it's clear that the internment of Japanese Americans was racially motivated. In response to Japan's growing military power in the buildup to World War II, President Roosevelt commissioned two reports to determine whether it would be necessary to intern Japanese Americans should conflict break out between Japan and the U.S. Neither's conclusions supported the plan, with one even going so far as to "certify a remarkable, even extraordinary degree of loyalty among this generally suspect ethnic group." But of course, the Pearl Harbor attacks proved to be far more persuasive than these reports.

Pearl Harbor turned simmering resentment against the Japanese to a full boil, putting pressure on the Roosevelt administration to intern Japanese Americans. Lieutenant General John DeWitt, who would become the administrator of the internment program, testified to Congress

"I don't want any of them here. They are a dangerous element. There is no way to determine their loyalty... It makes no difference whether he is an American citizen, he is still a Japanese. American citizenship does not necessarily determine loyalty... But we must worry about the Japanese all the time until he is wiped off the map."

DeWitt's position was backed up by a number of pre-existing anti-immigrant groups based out of the West Coast, such as the Joint Immigration Committee and the Native Sons and Daughters of the Golden West. For many, the war simply served as an excuse to get rid of Japanese Americans. In an interview with the Saturday Evening Post, Austin Anson, the managing secretary of the Salinas Vegetable Grower-Shipper Administration, said:

"We're charged with wanting to get rid of the Japs for selfish reasons. We do. It's a question of whether the White man lives on the Pacific Coast or the brown men. ... If all the Japs were removed tomorrow, we'd never miss them in two weeks because the White farmers can take over and produce everything the Jap grows. And we do not want them back when the war ends, either."

Ironically for Anson, the mass deportation of Japanese Americans under Executive Order 9066 meant there was a significant shortage of agricultural labor. Many Caucasians left to fight the war, so the U.S. signed an agreement with Mexico to permit the immigration of several million Mexicans agricultural workers under the so-called bracero program.

Life in the camps

Japanese American concentration camp

Hulton Archive/Getty Images

Circa 1943: Aerial view of a Japanese American relocation center in Amache, Colorado, during World War II. Each family was provided with a space 20 by 25 ft. The barracks were set in blocks and each block was provided with a community bath house and mess hall.

For the most part, Japanese Americans remained stoic in the face of their incarceration. The phrase shikata ga nai was frequently invoked — the phrase roughly translates to "it cannot be helped," which, for many, represents the perceived attitude of the Japanese people to withstand suffering that's out of their control.

Initially, most Japanese Americans were sent to temporary assembly centers, typically located at fairgrounds or racetracks. These were hastily constructed barracks, where prisoners were often packed into tight quarters and made to use toilets that were little more than pits in the ground. From here, they were relocated to more permanent camps — replete with barbed wire and armed guards — in remote, isolated places across the seven states of California, Arizona, Colorado, Wyoming, Idaho, Utah, and Arkansas.

Many of these camps, also known as War Relocation Centers, were little better than the temporary assembly centers. One report described the buildings as "tar paper-covered barracks of simple frame construction without plumbing or cooking facilities of any kind." Again, overcrowding was common.

As a result, disease became a major concern, including dysentery, malaria, and tuberculosis. This was problematic due to the chronic shortage of medical professionals and supplies, an issue that was not helped by the War Relocation Authority's decision to cap Japanese American medical professional's pay at $20 a month (about $315 in 2019 dollars), while Caucasian workers had no such restriction. As a comparison, Caucasian nurses earned $150 ($2,361) a month in one camp.

The U.S. government also administered loyalty questionnaires to incarcerated Japanese Americans with the ultimate goal of seeing whether they could be used as soldiers and to segregate "loyal" citizens from "disloyal" ones. The questionnaires often asked whether they would be willing to join the military and if they would completely renounce their loyalty to Japan. Due to fears of being drafted, general confusion, and justified anger at the U.S. government, thousands of Japanese Americans "failed" the loyalty questionnaire and were sent to the concentration camp at Tule Lake. When Roosevelt later signed a bill that would permit Japanese Americans to renounce their citizenship, 98 percent of the 5,589 who did were located at Tule Lake. Some apologists cite this an example of genuine disloyalty towards the U.S., but this argument clearly ignores the gross violation of Japanese Americans' rights. Later, it became clear that many of these renunciations had been made under duress, and nearly all of those who had renounced their citizenship sought to gain it back.

Since many children lived in the camps, they came equipped with schools. Of course, these schools weren't ideal — student-teacher ratios reached as high as 48:1, and supplies were limited. The irony of learning about American history and ideals was not lost on the students, one of whom wrote in an essay --

"They, the first generation [of Japanese immigrants], without the least knowledge of the English language nor the new surroundings, came to this land with the American pioneering spirit of resettling. ...Though undergoing many hardships, they did reach their goal only to be resettled by the order of evacuation under the emergency for our protection and public security."

Potentially the best part of life in the camps — and the best way for determined prisoners to demonstrate their fundamental American-ness — was playing baseball. One camp even featured nearly 100 baseball teams. Former prisoner Herb Kurima recalled the importance of baseball in their lives in an interview with Christian Science Monitor. "I wanted our fathers, who worked so hard, to have a chance to see a ball game," he said. "Over half the camp used to come out to watch. It was the only enjoyment in the camps."

The aftermath

When the camps finally closed in 1945, the lives of the incarcerated Japanese Americans had been totally upended. Some were repatriated to Japan, while others settled in whichever part of the country they had been arbitrarily placed in. Those who wished to return to the West Coast were given $25 and a train ticket, but few had anything to return to. Many had sold their property to predatory buyers prior to being incarcerated, while theft had wiped out whatever else they had left behind. Many, many years later, the 1988 Civil Liberties Act mandated that each surviving victim be paid $20,000, though that seems like a small fine to pay for irrevocably changing the courses of more than 100,000 lives.