Throughout the history of our planet several hundred magnetic reversals have occurred but modern humans did not exist at the time of the last full reversal so is it about to happen again and if so how will it affect us?
The Earth’s magnetic field surrounds our planet and serves to deflect most of the solar wind from space that would otherwise erode the ozone layer that currently protects the earth and all it inhabitants from ultraviolet radiation.
The magnetic field is generated by the flow of liquid iron in earth’s outer core. The liquid iron generates electric currents, which in turn produce magnetic fields. Charged metals passing through these fields go on to create electric currents of their own, and so the cycle continues.
A complete magnetic reversal describes when the magnetic north and south poles swap places however during a reversal it’s not as clear cut as this. During a reversal, the magnetic field will not be zero but will assume a weaker and more complex form. It could fall to just 10 per cent of its current strength and have magnetic poles at the equator. It could even have the simultaneous existence of multiple “north” and “south” magnetic poles as shown in the graphic below.
In the last 10 million years, there have been, on average, 4 or 5 reversals per million years however geomagnetic reversal are far from periodic. The interval between reversals are very irregular and can range up to tens of millions of years. Their duration is also inconsistent, the latest reversal, the Brunhes–Matuyama reversal, occurred 780,000 years ago, and may have happened within a human lifetime whilst some have lasted 10,000 years.
So why do we believe one is imminent?
The simple truth is that we are “overdue” for a full reversal and the fact that the Earth’s field is currently decreasing at a rate of 5 per cent per century, has caused many to suggest that the field may reverse within the next 2,000 years.
The rare field reversals are most likely caused by larger changes in the flow in the outer core, therefore, scientists must look here for answers. However, predicting Earth’s weather is an ongoing challenge scientists face so the idea of forecasting the behaviour of the core is an even more daunting prospect. Hope comes in the form of the European Space Agency satellites which are providing unparalleled insights into the structure and behaviour of Earth’s magnetic field. These eyes in the sky also measure how the magnetic field is changing, which gives us insight into how the liquid core is moving.
The recent discovery of a jet-stream within the core thanks to orbiting satellites highlights our increasing ability to measure and infer the dynamics of the core. The prospect of being able to forecast the Earth’s core is therefore perhaps not too far out of reach.
But what exactly would the effects of a reversal be?
We know that during a magnetic reversal the magnetic field will weaken and therefore its shielding effect will be reduced allowing increased levels of radiation to reach Earth’s surface. The effects of high levels of charged particles entering Earth’s atmosphere would be severe disruption to satellites, aviation, and ground-based electrical infrastructure.
The impact of a prolonged absence of electricity, heating, air conditioning, GPS or the internet would be widespread and would likely result in severe economic disruption measuring in tens of billions of dollars a day.
However, despite all this, it is clear that early humans did manage to live through the Laschamp event and life itself has survived the hundreds of full reversals evidenced in the geologic record. Therefore despite the loss of many systems upon which we have come to rely, humanity as a species has a good chance of surviving such an event.