By Gwynne Dyer
For a moment there I thought we had a new global threat to deal with. This would have been welcome from a journalistic point of view, since there is a constant need for scary new topics to write about. Otherwise we would fail in our primary task, which is to provide material to hold the ads apart.
I was also experiencing some personal indignation, since the imminent reversal of the Earth’s magnetic field seemed to threaten one of the few practical skills I have retained from my early career in various navies: the ability to navigate by magnetic compass.
The navy knew that in a major war all the externally-based navigational aids (mostly satellite-based GPS nowadays) would quickly be shut down or blown away. One internal power failure and we would lose our gyro-compass too.
We would then have to fall back on the primary pre-20th century navigational tool, the magnetic compass, which does not depend on an external power supply. Unfortunately, the magnetic compass points at the Magnetic North Pole, which is in a different place from the true North Pole.
The Magnetic North Pole wandered a bit over time, but it stayed in a relatively small tract of territory among Canada’s Arctic islands. So all the charts showed the difference (‘variation’) between True North and Magnetic North, and by applying that difference we could steer and navigate accurately using the magnetic compass.
It was a skill for which there was a very limited demand, but potentially useful in an emergency.
Alas, the Magnetic North Pole left home about 30 years ago, and is now heading for Siberia at a speed of 60 km. a year.
Navigators can cope with this because computers make it easy to update charts to give the current local magnetic variation from True North. The worry is that this sort of behaviour by the magnetic pole is believed to signal an impending ‘flip’ in which the north and south magnetic poles change places.
The Earth’s magnetic field has reversed its polarity at least 183 times before, and it makes no long-term difference. The other end of the needle will now point to ‘Magnetic North’, but the magnetic field will still fulfill its primary function of trapping the high-energy particles that would otherwise bathe the planet’s surface in hard radiation.
The scary bit is the transition, which can take as long as a thousand years or as little as one lifetime, because during that transition the strength of the planet’s magnetic field falls to around 5% of normal. If the ozone hole worried you a bit, this should frighten you to death – and the strength of the magnetic field is already falling.
That was my initial reaction to the news. Every decade seems to bring news of yet another way that the universe can kill us. But not, it turns out, this one.
The consensus among scientists is that the surface of the planet is not bombarded by hard radiation during the intervals when the Earth’s internally generated magnetic field all but disappears for a time. Instead, the solar wind itself induces a magnetic field in the extreme upper limit of the planet’s atmosphere (the ionosphere) that stops incoming high-energy particles from reaching the surface.
We may have the opportunity to check the validity of this prediction in the relatively near future, but for the moment there is no need to panic. And if you’re lost in the woods (or at sea), you can still trust your compass. More or less.
