Photograph by Peter Mather, Nat Geo Image Collection
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If the poles reverse—and the magnetic field weakens—we could see auroras, like this one in Canada's Yukon territory, at lower latitudes.

Photograph by Peter Mather, Nat Geo Image Collection

Earth's Poles Will Eventually Flip, So What Then?

From animal migrations to human communications, a reversal of Earth’s magnetic poles could seriously mess with life as we know it.

Many facets of our lives depend on the Earth’s magnetic field, anchored by the North and South poles, from the electrical grid that powers our computers to the satellites that let us watch TV. Turtles and other creatures navigate with it. But as Alanna Mitchell shows in her new book, The Spinning Magnet, it wasn’t always that way. Indeed, as little—in geologic time, anyway—as 780,000 years ago, the poles reversed. It may be about to happen again, some scientists believe, with potentially disastrous results for life on Earth. (Why it's not time to panic yet about the magnetic field flip.)

When National Geographic caught up with her by phone from her home in Toronto, Mitchell explained how a scientist in Maryland has built a giant contraption to try and mimic the earth’s magnetic field; how satellites are peering more deeply inside the earth’s core than ever before; and why something called the South Atlantic Anomaly may presage a new polar reversal.

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We take it for granted, but right under our feet incredibly complex and volatile forces are at work. Take us on a journey to the center of the earth and explain how satellite technology is allowing us to get an unprecedented view inside our planet.

Such a great question! Over the last 100 years, scientists have been able to go beneath the crust of the Earth and look inside the core of the planet. They did that originally through seismology, and much more recently, looking at it mathematically, extrapolating from information satellites are giving us.

The magnetic field that protects our planet from solar and galactic radiation, the dangerous rays that can harm things on our planet, is generated in the outer core. As energy travels through that core it creates an electrical current, which in turn creates a magnetic shield that goes far out into space. In the 1980s, scientists started to send satellites up into the atmosphere and get these little glimpses of what was happening to the magnetic shield. Through math, they are able to take those calculations from outer space and look at what’s happening inside this molten outer core, where the field is generated.

What they have found is phenomenally surprising. There is this absolutely tortured bunch of magnetic fields within the core. You’ve got the two pole magnetic fields that protect our planet, the North and South poles, but within this molten core there are all these factions, like the battle of the Titans, that are trying to topple the dipole. If they succeed, which they’ve done hundreds of times in the planet’s history, then the North and South poles will switch places.

Many creatures have a so-called magnetic sixth sense. Explain how this works, and what harmful effects possible disruptions may have.

Scientists have found that all plants and animals respond to the magnetic field of our planet. Say you’re a whale trying to get up the coast of North America to where the good fish are in the spring, where you can fatten yourself up, breed and pass on your DNA. If you can’t figure out how to get there, by navigating with the magnetic field, then that may affect your reproductive strategy. Similarly, some turtles need to go back to the very same bay in Australia in order to lay their eggs. The concern is that they won’t be able to find that beach if they can’t navigate by the magnetic field, and they may end up going somewhere else.

Will it make enough of a difference to harm life on Earth? That part is not clear. We’ve got a situation on our planet right now where about one third of our planet’s creatures are already in danger, and some are critically in danger. So, you’re not talking about a time that is normal for life on Earth. The big question mark about the eventual switch of the poles is what effect it will have on creatures that are already severely compromised in their ability to go where they need to go.

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Electromagnetic disruptions in space can also be incredibly damaging to the technologies we depend on. Tell us about the magnetic storm of 2012 and how a British company has devised an algorithm for the insurance industry to calculate the cost of future storms.

Our electronic grids are very tightly interconnected, so a failure in one part of it can cascade across the planet. There was a near miss in 2012 from an absolute super-storm that the sun let loose. This massive, once-in-150-years event happened to be released when the sun was facing away from our Earth. Had it been a week or two earlier, it would have been directly facing our planet and the forensic analysis suggests that we would have been sent back to the Victorian age in terms of our electrical systems had that happened.

The fact that it was such a near miss and so well recorded by satellites allowed scientists to go to the governments and academics and say, “Look, this was a really close thing. It could have completely destroyed our electronic systems, shouldn’t we start preparing for that?” As a result, a group in the U.K. developed a way to look at what the economic costs of these big solar storms would be, and try to figure out what we can do to protect ourselves. The costs could be as much as $41.5 billion a day to the U.S. economy alone from a single storm. And that’s assuming it doesn’t spread past the U.S., which, of course, it would.

Let’s go back in time, to central France, and a scientist named Bernard Brunhes, whom you call “magnetism’s forgotten man.” Pull up a chair at his fireside for us and explain why he is so important.

Brunhes was a geophysicist who wanted to trace the Earth’s magnetic field over time. To do that, he needed a unique formation: a thick piece of undisturbed terra cotta that had then been covered by hot basal lava from a volcano. When terracotta is heated up, then cools down, some of the electrons in its molecular structure, will become fossil magnets. They will lay down the coordinates of the magnetic field on that exact spot of the Earth at that precise time, so you can see very precisely what was happening.

Brunhes lived near Puy de Dome in the Massif Central, in the middle of France, where there are all these extinct volcanoes. Word comes back from one of his friends, who was a road cutter, saying, “I just cut a road in this place called Pontfarin, and it showed just exactly what you’re looking for.” Brunhes packs his chisels, gets on his horse, rides for at least a day, then chisels out some pieces of the terra cotta with the basalt over the top of it, and takes it back to his laboratory.

What he discovers in the terra cotta is that when this terracotta got super- heated, and then cooled again, the poles were on different sides of the planet. This was an absolutely anguishing finding for scientists at that time. They had no way of explaining how or why this would happen. They also had no way of confirming that it had happened, so there was great doubt about his finding. As a result, he never published again on the topic and died a few years later of a massive stroke at the age of 42. But this was the first signal that the heart of the molten outer core of our planet is much more tortured than scientists had imagined.

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The magnetic field protects Earth from solar radiation.

Today, a professor at the University of Maryland is trying to build a working model of how the magnetic field inside the earth works. Tell us about Dan Lathrop and his "self-sustaining dynamo."

Constant movement within the outer core is what creates our magnetic field. What Lathrop is trying to do is re-create the dynamo that we believe exists inside the core of the Earth. But instead of the molten nickel and metallic stuff that’s within our actual core, he’s got this huge sphere filled with liquid sodium. It’s like an enormous metal ball spinning around. It’s so huge it’s got its own hangar on the Maryland campus. It’s very dangerous because the liquid sodium is enormously volatile. But several days a week this thing liquefies and spins and they take measurements of it and assess what it’s doing.

So far, it hasn’t been successful, or “dynamo-ed,” as the scientists like to say. It’s only created an amplification of the magnetic field. Lathrop wants to reproduce what’s going on in the core because he wants to see what conditions would have to be there for a reversal to take place. Everybody in the geophysics community is looking at this experiment because one of the great questions they’re trying to answer is when a reversal might happen.

So, how long have we got? And what could the consequences for life on earth of a polar reversal be?

We know that the Earth’s poles have reversed hundreds of times. It’s a dynamic system inside the outer core and it has to reverse at times because that’s just part of the way it works. We know it’s done this most recently 780,000 years ago, so there are people who say it’s overdue. We know that the core is becoming increasingly volatile. The North magnetic pole is absolutely running through the Northern Hemisphere at 55 kilometers a year to the northwest. That’s an indicator that something unusual is happening inside the core. We also know that the dipole is weakening fairly dramatically. If you look at satellite imagery, you can see that part of the magnetic field has already reversed in the Southern Hemisphere. This is something called the South Atlantic Anomaly. We know that that “reversed flux patch,” as scientists call it, is moving to the West and that it’s doubled in size in the last 60 years, so it now covers about 20 percent of the planet’s surface.

Does that tell us that a reversal is at hand? Scientists simply do not have enough information to make that conclusion. What they say is that it’s incontrovertible the poles will reverse again at some point. But they don’t know whether this is the beginning of it because they just don’t have enough information.

The consequences for life on Earth are potentially devastating. One scientist I spoke to, Daniel Baker, of the University of Colorado, who is an expert in radiation from the sun and how that affects our planet, says there’s no question in his mind that parts of the planet will become uninhabitable. But we can’t predict which those are going to be. What he means is that extra ultraviolet radiation that is damaging to human tissue and can cause mutations will hit the planet because we won’t have the magnetic shield to protect us.

What if one of those bands of extra radiation hits a very heavily populated part of the planet? Then, of course, there are the effects on all the creatures on the planet, as well as the effects on our electromagnetic system, the electric grid, and all the things we consider part of modern civilization.

This interview was edited for length and clarity.

Simon Worrall curates Book Talk. Follow him on Twitter or at