The Earth ‘magnetic field surrounds our planet as an invisible field of force – by deflecting charged particles away, protecting life from harmful solar radiation.
This field is constantly changing far from being constant. Indeed, the history of our planet includes at least several hundred global magnetic reversals, where magnetic poles swap locations between north and south. So when is the next one going to happen and how will it affect Earth’s life?
The magnetic field will not be zero during a reversal, but will assume a weaker and more complex shape. It may fall to 10% of the current strength and have magnetic poles at the equator or even multiple “north” and “south” magnetic poles simultaneously.
On average, geomagnetic reversals occur several times a million years. The interval between reversals, however, is very irregular and can be as high as tens of millions of years.
There may also be temporary and incomplete reversals, known as events and excursions, where the magnetic poles move away from the geographic poles – possibly even across the equator – before returning to their original locations.
Around 780,000 years ago, the last full reversal, the Brunhes-Matuyama, took place. A temporary reversal occurred about 41,000 years ago, the Laschamp event. With the actual polarity shift lasting around 250 years, it lasted less than 1,000 years.
Power cut or mass extinction?
During a reversal, the alteration in the magnetic field will weaken its shielding effect, allowing for increased radiation levels on and above the surface of the Earth. If this were to happen today, there would be increased risks for satellites, aviation and ground-based electrical infrastructure due to the increase in charged particles reaching Earth.
Geomagnetic storms, driven by the interaction with our magnetic field of anomalously large solar energy eruptions, give us a foretaste of what we can expect from a weakened magnetic shield.
The so-called Halloween storm in 2003 caused local electricity grid blackouts in Sweden, required flight re-routing to avoid blackout and radiation risk of communication, and disrupted satellites and communication systems.
But this storm was small compared to other recent past storms, such as the Carrington event of 1859, which caused aurorae as far south as the Caribbean.
It is not fully known the impact of a major storm on the electronic infrastructure of today. Of course, any time spent without electricity, heating, air conditioning, GPS or internet would have a major impact; widespread blackouts could result in tens of billions of dollars a day of economic disruption.
We cannot definitely predict what will happen in terms of life on Earth and the direct impact of a reversal on our species as modern humans did not exist at the time of the last complete reversal.
Several studies have attempted to link past reversals with mass extinctions–suggesting that a common cause could drive some reversals and episodes of widespread volcanism. There is no evidence of any impending cataclysmic volcanism, however, and we would probably only have to contend with the electromagnetic impact if the field were to reverse relatively quickly.
We know that many species of animals have some form of magnetoreception that allows them to feel the magnetic field of the Earth. They may use this to assist with migration in long-distance navigation. But the impact a reversal could have on such species is unclear.
What is clear is that early humans have succeeded in living through the Laschamp event and life itself has survived the hundreds of complete reversals shown in the geological record.
Can we predict geomagnetic reversals?
The simple fact that we are “overdue” for a complete reversal and the fact that the field of the Earth is currently declining at a rate of 5 percent per century has led to suggestions that the field may reverse in the next 2,000 years. But it will be hard to pin down an exact date – at least for now.
The magnetic field of the Earth is generated by the slow churning of molten iron within the liquid core of our planet. The way it moves is governed by the laws of physics, like the atmosphere and oceans.
Therefore, by tracking this movement, we should be able to predict the “core weather,” just as we can predict real weather by looking at the atmosphere and the ocean. A reversal can then be compared to a particular storm type in the core, where the dynamics –and the magnetic field –go through haywire (at least for a short while) before re-settling.
The difficulties of predicting the weather beyond a few days are well known, despite the fact that we live within the atmosphere and directly observe it. Yet predicting the core of the Earth is a far more difficult prospect, mainly because it is buried under 3,000 km of rock so that our observations are scarce and indirect.
We’re not completely blind though: we know the material’s major composition within the core and it’s liquid. A global network of ground-based observatories and orbiting satellites also measure how the magnetic field changes, giving us insight into the movement of the liquid core.
The recent discovery within the core of a jet-stream highlights our evolving ingenuity and increased ability to measure and infer the core dynamics. Our understanding is developing at a rapid rate in conjunction with numerical simulations and laboratory experiments to study the fluid dynamics of the interior of the planet. The prospect of being able to forecast the Earth’s core is perhaps not too far