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Tuesday, February 5, 2019

Magnetic north just changed. Here's what that means.

Magnetic north has never sat still. In the last hundred years or so, the direction in which our compasses steadfastly point has lumbered ever northward, driven by Earth's churning liquid outer core some 1,800 miles beneath the surface. Yet in recent years, scientists noticed something unusual: Magnetic north's routine plod has shifted into high gear, sending it galloping across the Northern Hemisphere—and no one can entirely explain why.

The changes have been so large that scientists began working on an emergency update for the World Magnetic Model, the mathematical system that lays the foundations for navigation, from cell phones and ships to commercial airlines. But then the U.S. government shut down, placing the model's official release on hold, as Nature News first reported earlier this year.
Now, the wait for a new north is over. The World Magnetic Model update was officially released on Monday, and magnetic north can again be precisely located for people around the world.
Questions still likely abound: Why is magnetic north changing so fast? What were the impacts of the update's delay? Was there really a geologic reason Google maps sent me off course? We've got you covered.

What is magnetic north?

Magnetic north is one of three “north poles” on our globe. First, there's true north, which is the northern end of the axis on which our planet turns.
But our planet's protective magnetic bubble, or magnetosphere, isn't perfectly aligned with this spin. Instead, the dynamo of Earth's core creates a magnetic field that is slightly tilted from the planet's rotational axis. The northern end of this planet-size bar magnet is what's known as geomagnetic north—a point sitting off the northwest coast of Greenland that's changed position little over the last century.
Then there's magnetic north, what your compass locates, which is defined as the point at which magnetic field lines point vertically down. Unlike geomagnetic north, this position is more susceptible to the surges and flows in the swirl of liquid iron in the core. These currents tug on the magnetic field, sending magnetic north hopping across the globe.
“The north magnetic pole is quite a sensitive place,” says Phil Livermore, a geophysicist at the University of Leeds.

What is the World Magnetic Model?

James Clark Ross first located magnetic north in 1831 in the scattered islands of Canada's Nunavut territory. Since then, the pole has largely marched north, traversing hundreds of miles over the last several decades. (Curiously, its polar opposite, magnetic south, has moved little during this time.)
To keep up with all these changes, the U.S. National Oceanic and Atmospheric Administration and the British Geological Survey developed what eventually became known as the World Magnetic Model, “so they would all be on the same map, essentially,” says Ciaran Beggan, a geophysicist with the BGS.
The model is updated every five years, with the last update in 2015. Between each update, scientists check the model's accuracy against data from ground magnetic observatories and the European Space Agency's Swarm mission—a trio of magnetic-field mapping satellites that zip around Earth 15 to 16 times each day. Until now, this seemed sufficient to keep up with magnetic north's march toward Siberia.
In the mid 1900s, the north magnetic pole was lumbering along at less than a hundred feet each day, adding up to less than seven miles of difference each year. But in the '90s, this started to change. By the early aughts, magnetic north was chugging along at some 34 miles each year.
Things are acting very strangely at high latitude,” says Livermore, who notes that this increase seemed to coincide with a strengthening jet in the planet's liquid outer core. Though the events could be linked, it's not yet possible to say for sure.
By early 2018, scientists realized that the model would soon exceed the acceptable limits for magnetic-based navigation. Something had to be done before the model's next regular update, slated for 2020.

Did the government shutdown upset GPS navigation?

To correct the model, NOAA and BGS scientists tweaked it using three years' worth of recent data. This updated version was pre-released online in October 2018. As Beggan explains, these include the model's primary users in defense and military—the U.S. Department of Defense, the U.K. Ministry of Defense, and the North Atlantic Treaty Organization.
The government shutdown delayed the comprehensive public release of the information, which includes online calculators, software, and a technical note describing the changes. In principal, everyone who uses GPS could benefit from this update, Arnaud Chuillat, a geomagnetist at the University of Colorado in Boulder and a NOAA affiliate who worked on the update.
The model has found its way into many of our modern mapping systems, including Google and Apple, Beggan adds. But the difference is minor for most civilian purposes, and the changes are mainly limited to latitudes above 55 degrees.
“The average user is not going to be overly affected by this unless they happened to be trekking around the high Arctic,” Beggan says.

What caused all this weirdness?

Interest in these unexpected jolts is about more than mapping. The dance of Earth's magnetic field lines presents one of the few windows scientists have to processes that happen thousands of miles below your feet.
At the 2018 American Geophysical Union fall meeting, Livermore presented what he calls a magnetic field “tug-of-war” that may offer an explanation for the recent odd behavior. The north magnetic pole seems to be controlled by two patches of magnetic field, he explains, one under northern Canada and one under Siberia. Historically, the one under northern Canada seems to have been stronger, keeping the magnetic pole in its clutches. But recently, that seems to have changed.
“The Siberian patch looks like it's winning the battle,” he says. “It's sort of pulling the magnetic field all the way across to its side of the geographic pole.”
This may be a result of a jet within the core smearing and thus weakening the magnetic field under Canada, he says. The jet's increase in speed seems to have coincided with the last few decades of the magnetic pole zipping north. But he cautions about jumping to any definite conclusions.
“There may well be a link there,” he says. “It's not certain, but it could be.”

What's next for magnetic north?

It's tough to predict what will happen to the magnetic north pole—or whether it's even going to maintain its speed as it staggers toward Siberia, notes Robyn Fiori, a research scientist with Natural Resources Canada. The only thing that seems certain about magnetic north is its unpredictability.
Rocks hold geologic maps of even weirder movements of the magnetic poles, suggesting that in the last 20 million years, magnetic north and south have flipped places multiple times. This seems to happen roughly every 200,000 to 300,000 years. The exact causes behind these reversals remains uncertain. But the latest movement shouldn't have you in knots about an imminent flip.
There's no indication that there's a reversal,” Beggan says. “And even if there was a reversal, geological records show these things tend to take a few thousand years, at the very least.” (What really happens when the magnetic field flips? Here's what we know.)
Models of magnetic north suggest that this latest leap isn't even the strangest thing the pole has done in more recent history, Fiori adds. Before 1900, its wanderings likely once had a lot more wiggle and may include several hairpin turns in northern Canada that could have sent the pole on a brief southward stint.
“It all has to do with changes in the fluid motion of that inner core,” she says. It's therefore hard to say if magnetic north's newfound speed is the new normal.
“We know that the pole now is moving faster than it has for decades, but how often does that happen in the long historical record?” inquires Geoff Reeves, a space scientist at Los Alamos National Lab.
“We don't have any idea. What we know is what it's doing now is different, and that's always exciting scientifically.”

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