The Earth’s magnetic field is an extremely important component contributing to the existence of life on our home planet, providing a protective shield against the otherwise harsh solar wind. The magnetosphere, much like Earth’s other spheres, is not static, and instead undergoes constant regional fluctuations, including the periodic phenomenon of complete polar reversals. These geomagnetic reversals are a concern to scientists, in that we neither have any way of predicting when they will happen, nor do we actually know how such a phenomenon would affect life on Earth.
Our magnetic field is thought to be generated by differences in the flow of the planet’s outer core, being composed of mostly liquid iron and nickel. Heat from the solid inner core drives currents that have been observed in the outer core, and the coriolis effect organizes these currents into regional zones that act as large electrical generators, and in turn, that electrical current generates a series of magnetic fields.
Combined together, these individual fields form the Earth’s magnetosphere, a large magnetic field that reaches out into space, acting as a shield that deflects the charged particles that make up the solar wind. Without this protection, these charged particles would slowly erode away the atmosphere, and periodic lethal doses of radiation would reach the planet’s surface.
Studies of the geological record have determined that the Earth’s magnetic field has flipped at what appear to be random intervals throughout the planet’s history, with periods between the reversals lasting between 100,000 to 1 million years. While most reversals can take between 1,000 and 10,000 years to complete, the last full event, the Brunhes–Matuyama reversal that occurred 780,000 years ago, is believed to have only taken a few decades to complete. A brief reversal that occurred 41,000 years ago only lasted for less than 500 years, before reverting back to its previous polarity.
In the leadup to these reversals, the planet’s magnetic field weakens, as it is currently being observed doing. There is, however, a problem in trying to predict precisely when these reversals happen: as it is, we have trouble predicting the weather in the atmosphere, a phenomenon that we’ve been studying since the beginning of humanity, while our study of the various interior spheres of the Earth is barely a century old. While it is considered that we’re due for a pole reversal, based on the time since the last reversal being well past the 450,000-year average between full reversals, this event might begin tomorrow, or it mightn’t happen for another 200,000 years. But along with our inability to predict when it will occur, we also aren’t quite sure what the effects of a reversal would entail.
The light displays generated by aurorae, both Borealis (northern hemisphere) and Australis (southern hemisphere) would likely become more frequent, and appear closer and closer to the equator. The effect on animals that rely on magnetoreception — the ability to sense magnetic fields, affecting, for instance, the long-distance navigational ability of birds — is unknown: would the animals be confused as to their orientation, or do they have a built-in instinct that quickly adapts to these changes?
The effect that might pose the greatest problem would be the weakening of the magnetosphere’s shielding effect, allowing the solar wind’s charged particles to reach the surface. This could potentially produce negative health effects from increased radiation exposure. However, studies that have tried to link previous pole reversals to extinction events haven’t found a correlation between these two phenomena. Humans have also survived numerous reversals over the course of the species’ history, meaning that, as a species, the phenomenon is unlikely to wipe us out.
Our electrical technology, however, is not nearly as robust as out biology: strong solar storms have been known to disrupt electrical equipment in orbiting satellites, but also at the surface, including systems as broad as regional energy grids. It is estimated that a solar event as strong as 1859’s Carrington event could cause a major disruption of energy grids, nation wide, to the point where they may fail altogether: if the magnetosphere were to weaken, that could potentially allow lesser storms to cause the same catastrophic damage. Whitley Strieber outlined the dangers of such storms in his 2012 ebook, Solar Flares: What You Need to Know.