Why does the magnetic north pole move, and why is it moving so quickly?
The magnetic field is created by the liquid outer core that starts about halfway to the centre of the Earth. You’ve got this large, convecting layer of liquid metal and, as it moves, it creates the magnetic field, but it also drags the field with it.
The reason the magnetic north pole is moving is because, we think, a fast jet of liquid has formed – a sort of jet stream – at the high latitudes up around northern Canada, and it’s pushing the magnetic field in this area rapidly.
If you look back at how the magnetic north pole has moved in the last hundred years or so, you’ll see that from 1900 to 1990 the average rate of change of the pole’s position was about 5 to 10 kilometres per year, and in the 1990s it suddenly started accelerating. At the moment, it’s moving at about 50 or 60 kilometres per year.
How’s that going to affect the average person?
The map application in mobile phones or in-car navigation systems use magnetic field maps made by the British Geological Survey and the US National Oceanic and Atmospheric Administration. We create those maps every five years to make a prediction about how the field will change in the following five years. The last one was released in 2015. The next one was scheduled to be released in 2020, but because the magnetic north pole had moved further than we expected, by 2018 the map was already out of date. So, we were asked to update the map.
For the average person, unless you’re planning to traipse around the Arctic in Canada or Siberia, you wouldn’t really notice the difference, because the magnetic field maps we make for lower latitudes – below the latitude of Scotland, say – are actually fairly decent. They’re not too much in error. But the maps of the high Arctic are out, because the magnetic field moved so quickly.
The digital compass in your smartphone is only accurate to a degree or two, and the differences between our latest update of the map and the previous update of the map, for most people, will only be a fraction of a degree.
Who needs high-precision maps of the magnetic field?
Mainly the people who fly aircraft over those regions. Most aircraft maps are orientated in magnetic coordinates for historical reasons, so these maps are important for aircraft, say, flying from London to San Francisco: they fly over the northern Arctic. What would happen is that the plane would drift maybe a few tens of kilometres out from where it should be, though that should be corrected by GPS. The other main users are the UK and the US military, which use it in navigation systems in submarines and aircraft and so on.
How do we know the history of the magnetic pole’s position?
Magnetic coordinates have been used for ship navigation for hundreds of years, and we’ve got ship records, logs and log books going back to at least the 1590s. You can use those to work out where the magnetic north was by looking at all the measurements. This tells us that from the 1500s onwards, the magnetic north pole wandered around Canada more or less in erratic zigzags.
It wasn’t until the 1900s that it started moving westwards, towards Siberia, and it’s been accelerating that way for the last 30 years or so. Up until the 1990s, there were around 200 geomagnetic observatories where we measured the field continuously. Since 2000, a number of satellites have been launched into low-Earth orbit, up to about 400 kilometres. They fly around continuously measuring the magnetic field and its direction.
Why did sailors start using the magnetic north pole?
The idea was originally from Edmond Halley, of comet fame. They knew how to measure latitude, by looking at the height of the Sun in the sky, but to measure longitude was more difficult. They tried to do it by looking at the variation in the angle between true north and magnetic north – that’s called declination.
In 1699, Halley went out in a ship and surveyed the Atlantic Ocean and drew up the original maps of the magnetic field. When he went out and looked again, he realised that the angle had changed so quickly that his maps were out of date within five or ten years. He thought: “How is it that the magnetic field is changing?”
Then he made the most amazing leap, and suggested that there must be a layer of liquid somewhere within the Earth that was causing the magnetic field to move. He was the first person to dream up the idea of an outer core. It wasn’t confirmed until 1906, by seismological data.
What can we expect the magnetic north pole to do in the future?
We have no idea. We’re a bit like weather forecasters 100 years ago: we have a general idea which way the wind is blowing at a few points along the coast, and so we could make a general prediction that the wind will probably still be blowing that way tomorrow.
But for us to make a detailed forecast of what will happen to magnetic north, even a few days later, is beyond our abilities, because we cannot yet measure the magnetic field at the edge of the outer core accurately enough to understand how the liquid is flowing.
Listen to our full interview with Dr Ciaran Beggan in theScience Focus Podcastbelow.
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