SA in pole position for magnetic shift
Cape Town - Earth’s magnetic field is undergoing significant shifts, and South Africa has front row seats to observe the changes.
Satellites and magnetic observatories have recorded stirrings in the magnetic field – some areas weakening, some strengthening – which suggest that our planet is headed for a reversal of its magnetic poles in the next few hundred years.
If that happens, compasses which usually point north will point south. Animals which use the magnetic field for navigation such as birds, whales and sharks will find it difficult to migrate along their usual routes. Our magnetic navigation systems will have to be recalibrated.
And while South Africans won’t be able to watch the aurora visible over the equator during the pole switch, we are in a prime position to monitor the process because we are situated between the two areas of greatest change in the magnetic field.
Just south-west of Cape Town is the region where the largest decrease was recorded by satellites between 1980 and 2001: -8 percent. And not too far east of South Africa is the region in the Indian Ocean where the largest increase was recorded, of +3 percent.
At the magnetic observatory in Hermanus, one of four in the country, the geomagnetic field has decreased by more than 20 percent since 1941.
Dr Pierre Cilliers, a researcher at the South African National Space Agency (Sansa), said: “The area of largest decrease in the magnetic field is closer to South Africa than to the rest of the inhabited world.”
This is because the weakest area of our planet’s magnetic field falls mostly over the Atlantic Ocean. This area is called the South Atlantic Magnetic Anomaly (Sama), and it stretches from our country westward across the sea towards South America.
The Sama exists because in that region, 3 000km below the surface, the electric currents which flow in the molten outer core – and are believed to create the magnetic field – are flowing in the opposite direction.
Another researcher at Sansa, Dr Pieter Kotze, said “the effect of this discrepancy is that the area of the magnetic field over the South Atlantic Ocean is approximately 30 percent weaker than the rest of the world at similar latitudes”.
The size of this magnetic anomaly has grown substantially over the past 400 years.
Polarity flips only happen every few hundred thousand years, so nobody alive knows what it is like to experience one, or how it will affect life on Earth.
Kotze thinks it most likely that people with sensitive skin will have to be more careful in direct sunlight, as “energetic particles from outer space will be able to penetrate the atmosphere to much lower altitudes than is currently the case”, weakening the ozone layer.
This is because during a polarity reversal the magnetic field must drop to between 10 and 20 percent of its usual strength.
Kotze wrote in a recent newsletter that “the shielding effect of the magnetic field protects the Earth from the impact of solar wind and other harmful radiation.
“Without it, solar wind would erode our atmosphere and life on Earth as we know it would be unable to exist.”
However, Kotze said, with a weakened magnetic field, the atmosphere of the Earth would act as the primary protective layer. He said periods of mass extinctions have never coincided with a polarity reversal – so the effects on Earth are not likely to be catastrophic.
It is impossible to say for certain when the polarity reversal will take place, or how long the process would take.
Kotze says computer simulations have revealed that it could take between 3 000 and 5 000 years to complete.
What is certain, though, is that the signs observed suggest we are heading for one.
BBC News Online science editor Dr David Whitehouse said: “Such events occur about every 250 000 years. However, it has been 750 000 years since the last reversal – so we are certainly overdue.” - Weekend Argus