Is there any way humans could influence whether/when a magnetic pole flip happens?

Question

Are there any actions that humans do that could influence whether a magnetic flip (I believe the proper name is geomagnetic reversal) happens? Are there any ways humans could theoretically influence the planet's magnetic field in a significant way? (Intentionally or not).

Nothing here is really off limits, human-caused climate change/global warming, nuclear weapons, things we haven't invented yet (that are still at least somewhat feasible).

But to try and ground it lets say using technology that could reasonably be invented in the next 100 years.

Answer 1

I will argue that this isn't possible - not within the next century, and possibly never unless we're willing to sacrifice habitability.

I'm a little skeptical of the prospect of achieving a reversal by applying an external magnetic field. There's strong evidence that the mantle can act similarly to a semiconductor, meaning that changes on timescales of months to years are significantly shielded (Currie 1967). Put another way, to in any way affect the core via a magnetic field, you'd likely need to maintain a strong external field for something like decades, which would be extremely difficult to do; the energy required would not be small. If you're capable of overcoming that, then great, but it does seem like a tall order if we're restricted to the next century's worth of technology.

(Bear in mind that we're dealing with currents on the order of $I\sim10^8$ Amps, which is something like four orders of magnitude higher than the current in a lightning strike. Given the size of Earth's core, the current density isn't enormous, but I do want to point out that we really are playing with fire here.)

There have been claims that other phenomena have caused geomagnetic reversals in the past, and those mechanisms may be worth investigating. Given that the flow within the core is chaotic, it's possible that relatively small perturbations to the flow, such as from plumes poking down from the mantle, could cause a reversal. The question, then, is how we could achieve this. It's tempting to suggest an impact event or something like it (Muller & Morris 1986), although the required impact would be absolutely devastating to humans, so perhaps it would be best to avoid that one. Trying to modify plate tectonics to influence subduction also seems to fall into the category of "Please don't do that" events.

A final note: We don't have a great understanding of geomagnetic reversals, nor do we have a phenomenal picture of the details of the dynamo processes at work in the core. This is partly why I'm so cautious about the prospect of successfully influencing the extremely complicated processes happening at the center of the planet.

Answer 2

The magnetic field of the Earth is caused by an electric, self sustaining current in the molten core of the Earth (dynamo). If you apply a huge magnetic field to the circular current (to the surface it encloses), the current will reverse as reaction to the magnetic field you made appear inside. The field has to be increased in the same direction as the inside Earth magnetic field. The current will react to the increasing magnetic flux by reducing its strength and even reverse if the field is further incressed. The field due to the current is then opposite to its former direction. Then you have to reverse the outside field slowly (much slower than the initial increase). This will cause the field due to the current to stay as it is (hysteresis). So you end up with a flipped, man-induced magnetic field.

Answer 3

I can think of several possibilities that might become feasible in the next century.

Dropping a nuclear reactor into Earth's core. A large, very hot nuclear reactor could conceivably melt its way through the crust and mantle all the way down to the core. The reactor could be designed to target a particular destination in the outer core, which would be chosen based on suitable measurements and modeling. Upon arriving, it would increase its power output dramatically. The heat would disrupt the dynamo that drives Earth's magnetic field, causing a geomagnetic reversal.

How much nuclear fuel would be required? As an order-of-magnitude estimate, we might guess that the reactor would need to produce about 50 TW (the approximate total heat flow from Earth's interior to the surface) for a decade to have a significant effect. To do this, it would need to burn about

$$\frac{(50 \times 10^{12} \text{ W}) \cdot (10 \text{ years}) \cdot (235 \text{ g/mol})}{(\text{Avogadro's number atoms/mol}) \cdot (200 \text{ MeV/atom})} \approx \text{200,000 tons}$$

of fuel. The world currently produces around 60,000 tons of natural uranium per year. Although only about 0.7% of that uranium is the fissile isotope uranium-235, a well-designed fast breeder reactor could convert (most of) the remaining uranium-238 into fissile plutonium-239 and then burn it. So this seems difficult but potentially feasible, especially if we assume some technological advances over the next century.

Building a very large superconducting magnet. A loop of superconducting wire encircling the entire planet could generate a magnetic field strong enough to directly counteract the natural field from the core.

How much superconducting wire would we need? Suppose we need to generate a field of 1 gauss at the center of the current loop. That's about twice the strength of the planet's natural magnetic field, so it should be enough to reverse the field's direction. The required current would be about

$$\frac{\text{1 gauss} \cdot 2 \cdot \text{radius of Earth}}{\mu_0} \approx 10^9 \text{ A}$$

Suppose that we are building the magnet from magnesium diboride, a reasonably high-performance superconductor that can be made from commonly available elements. If we assume a current density of $500 \text{ kA/cm}^2$, which is the reported critical current density for a sample of high-quality bulk magnesium diboride, the wire would need to have a cross-sectional area of $0.2 \text{ m}^2$. Since the density of magnesium diboride is about $2.6 \text{ g/cm}^3$, the total mass of superconductor required would be around

$$0.2 \text{ m}^2 \cdot (2 \cdot \pi \cdot \text{radius of Earth}) \cdot 2.6 \text{ g/cm}^3 \approx \text{20 million tons}$$

Every year, the world currently produces around a million tons of magnesium and a few million tons of borates. Converting all of this raw material into superconducting magnesium diboride and building a suitable refrigeration system would be difficult and very expensive. But if we really wanted to do it, a century would be more than enough time.

Generating a large electrical current in the magnetosphere. Instead of building a new superconducting magnet, we could take advantage of the large body of conductive plasma that already exists around Earth: the magnetosphere. Again, a sufficiently large electrical current (around $10^9$ amps) could generate a magnetic field strong enough to counterbalance the natural field and trigger an effective geomagnetic reversal.

There are a number of ways to create electric currents in a plasma. For example, one can use an antenna array to broadcast radio waves parallel to the existing magnetic field. The waves are absorbed through Landau damping, exerting a force that drives an electric current. As the generated current becomes large, the direction of the overall magnetic field rotates. One can then move the antenna array to transmit parallel to the new field direction, and continue the process until the field has completely reversed.

Could we create a strong enough current in this way? It's difficult to accurately estimate the power required, as many processes in the magnetospheric plasma are nonlinear. We'd certainly need something bigger than HAARP, but perhaps not that much bigger. The solar wind (tens of gigawatts) is enough to drive the ring current of about 10 mega-amps, despite very low efficiency. So a well-designed space-based antenna array, in a high orbit (for lower plasma resistivity), with a few gigawatts of total transmit power, might possibly be sufficient.