There has been much discussion recently about the Earth’s changing magnetic field and not a few dramatic headlines portending dire consequences for humanity.
A series of space probes called Swarm built by the European Space Agency (ESA) has found that in an area stretching from Africa to South America the Earth’s magnetic field is gradually reducing in strength. An ESA press release said that this strange behaviour has geophysicists puzzled and is causing technical disturbances in satellites as they pass through an area called the ‘South Atlantic Anomaly.’ The South Atlantic Anomaly is a well-known region of weaker than normal magnetic field that has caused satellites problems ever since we started putting them into orbit. But there have been more satellite problems in that area than before.
Broadly speaking our Earth is two different planets, one of them nestling inside the other. The outer section is made of rock and is an excellent insulator. Inside our rocky exterior is a world of solid and liquid metal. The inner core is solid iron surrounded by the molten outer core. The motions in the outer core are the origin of our magnetic field via a dynamo effect. This magnetic shield protects us from the harshness of the cosmos. Life on our planet could not have survived without it.The weak region called the South Atlantic Anomaly.
Our magnetic field is not behaving in an unusual way. In fact, it is stronger than it has been on average over the past million years or so, more than twice as strong. Looking at the strength of the Earth’s magnetic field over the past 10,000 years shows it to have been weaker than today until about 2000 BC when in less than a thousand years it greatly increased in strength, at which it has stayed ever since. It has declined a little in the past few hundred years, but that decline is consistent with the up and down variations seen over the past few thousand years. This suggests that the Earth’s magnetic field is not doing anything dramatic at present, despite what the headlines say from time to time.
Our magnetic field does change dramatically from time to time. It weakens to a point where the usual north-south dipole configuration fragments allowing solar particles to strike the Earth’s atmosphere at all latitudes instead of polar ones causing aurorae all over the planet instead at just the poles. It last happened about 800,000 years ago. When the magnetic field grows again it does so with the opposite magnetic polarity.
There are some indications that our magnetic field can also change rather dramatically in shorter periods. About 41,400 years ago, give or take 2,000 years during the last Ice Age something happened to the earth’s magnetic field, something remarkable and very, very swift. Observations of the magnetic properties of sediments laid down in the Black Sea, and beryllium and carbon isotopes in Greenland ice cores, indicate that a geomagnetic reversal took place with astonishing rapidity. In 250 years the earth’s magnetic field declined by 95%, flipped for 440 years when the north magnetic pole was at the south and vice versa with a rather weak strength prepared to its pre-flip level, and then over another period of 250 years or so things reverted back. Scientists call it the Laschamp event after the Laschamp lava at Claremont Ferrand in the Masssif Central in France.
So whilst scientists are always monitoring the strength of the Earth’s magnetic field and chase the exact position of the magnetic poles which wander die to turbulent motions in the outer core, there is no indication of anything unusual at the moment.