Puzzled experts say the "strange behaviour" is causing trouble for satellites and aircraft – and some think it could be an early sign that Earth's magnetic poles will soon flip.
Earth's magnetic field keeps us safe
Earth's magnetic field is vital to life on our planet.
It's an ever-changing force that protects us from cosmic radiation – and charged particles from the Sun.
The field is mostly generated by the ocean of super-hot liquid iron that makes up the outer core of Earth, around 3,000km below our feet.
It creates electrical currents that generate (and change) our electromagnetic field.
But the field is getting weaker: over the last 200 years, it's lost around 9% of its strength globally.
Our magnetic field is weakening – especially in South America
Now scientists have noticed a particular patch of reduced intensity, which has developed between South America and Africa.
It's called the South Atlantic Anomaly, and it's constantly changing.
Between 1970 and 2020, its minimum strength has dropped from 24,000 nanoteslas to 22,000, as tracked by the European Space Agency.
And the area has grown and moved westward at around 20km per year.
A second centre of reduced intensity has also appeared in the last five years, just southwest of Africa.
This could mean that the South Atlantic Anomaly may split up into two parts.
"The new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade and in recent years is developing vigorously," said Jürgen Matzka, from the German Research Centre for Geosciences.
"We are very lucky to have the Swarm satellites in orbit to investigate the development of the South Atlantic Anomaly.
"The challenge now is to understand the processes in Earth's core driving these changes."
Magnetic pole reversal fears
Some scientists fear that the Earth's weakening magnetic field could mean Earth is heading for a pole reversal.
That would mean the north and south magnetic poles would switch places.
This has happened fairly regularly throughout Earth's history, approximately once every 250,000 years.
We're currently "overdue", because the last flip was around 780,000 years ago.
There's no evidence that this will happen soon, as fluctuations are common.
But satellites and spacecraft flying in the area are more likely to experience technical malfunctions due to the weaker magnetic field.
Magnetic north is MOVING
This "weakening" isn't the only big change happening to Earth's magnetic field, either.
Recent studies have also shown that the magnetic North Pole is rapidly changing.
Geographically, the North Pole never changes – but magnetic north does.
It's caught in a tug of war between two magnetic "blobs" deep below Earth's surface.
One of these "blobs" is in Canada and the other is in Siberia.
It's the latter blob that's winning, which is why magnetic north is drifting towards Siberia from the Canadian Arctic.
This has been the case since it was first measured in 1831, but its pace has sped up since the 1990s.
It was previously wandering at a rate of 0-15km per year, but it's now moving at 50-60km a year.
It means that the World Magnetic Model needs to be updated more frequently.
That's a vital navigation system, and is even used to guide our smartphones.
The way these "blobs" move and stretch dictates Earth's magnetic field.
"We can now pinpoint that a change in the circulation pattern of flow underneath Canada has caused a patch of magnetic field at the edge of the core, deep within the Earth, to be stretched out," said Phil Livermore, of the University of Leeds.
"This has weakened the Canadian patch and resulted in the pole shifting towards Siberia."
Pole reversals – the key facts
Here's what you need to know…
- A geomagnetic reversal is when the magnetic north and south poles switch
- That's not the same as geographic north and south – which don't move
- It means a compass designed to point to the North Pole would face the complete wrong direction
- Reversals have happened at least 183 times over the last 83million years
- The most recent was called the Brunhes-Matuyama reversal, which happened 780,000 years ago
- Experts believe it takes around 7,000 years for a reversal to complete
- A reversal happens spontaneously, due to the dynamic and unpredictable nature of Earth's liquid core
What's currently unclear is whether the pole will ever go back towards Canada.
At present, the pace is only increasing towards Siberia – but that might not always be the case.
"Models of the magnetic field inside the core suggest that, at least for the next few decades, the pole will continue to drift towards Siberia," explained Dr Livermore.
"However, given that the pole’s position is governed by this delicate balance between the Canadian and Siberian patch, it would take only a small adjustment of the field within the core to send the pole back to Canada."
In other news, Nasa has published mind-blowing photos of the surface of Mars.
The US military is developing a secretive network of spy satellites that will one day blanket Earth's orbit.
And Brits took stunning snaps of Elon Musk's Starlink satellites passing over the UK in April.
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