Magnetic North Pole fleeing Canada
On Dec. 10, the World Magnetic Model used to calibrate compasses was officially updated. The “model” can be thought of as a map that you would use, given your location on or near the Earth’s surface, to find out how many degrees your magnetic compass is off from true geographic north (or south). This ordinarily happens every five years, but the wizards in charge of the system decided to update a year early because the north magnetic pole is moving particularly fast right now.
As most Canadians will have heard, magnetic north is, at the moment, fleeing Canadian territory and heading toward Russia. The rate of change is still very high by historic standards, first established in the early 19th century, but it has slowed just a little. In the year 1900 the pole was firmly in the Canadian Arctic, off Somerset Island. It wandered north, broke out of our high Arctic archipelago in about 2000, and has been streaking Siberia-ward across the open sea at more than 50 km a year since. The time component in the new WMM forecasts a slight slowing over the next fiveyear period, to about 40 km/ yr.
This, like everything else involving Earth’s magnetic field, is a bit of a guess. The WMM has to be updated often because it does incorporate guesswork about the magnitude and direction of changes in the short-term future. The model will be most accurate now, and increasingly less so over the fiveyear term as the magnetic poles do their little dance — independently, by the way; the magnetic poles are not exactly opposite the Earth from one another, and the “south” one is scooting along much more slowly than the “north.” ( Also, the magnetic North Pole, the one to which the “north” needle of your compass is attracted, is actually a “south” pole to physicists.)
The truth is that the naive inquirer should not research Earth’s magnetism in the expectation that it is as well understood by scientists as, say, oceanic tides. ( You can probably detect that I am talking about myself here.) The question “Why is the magnetic pole leaving Canada?” does not really admit of a solid answer. Maybe it’s the investment climate?
Probably most everybody is dimly aware that the magnetic poles flip outright from time to time — every half- million years on average. But the assumptions embedded in your hand-held compass run much deeper than that. The Earth itself is only a big dipole magnet generally, rather than locally, and there is no guarantee of only one “north magnetic pole” as the field is measured near the surface. Competing “north poles” can form. ( Which would, at least, let Russia and Canada each have their own ...)
The influences on the magnetic field include everything from ocean currents to cosmic rays, but most of the action is happening in the planet’s metallic interior — which we can’t explore very easily. We also have no easy way of pushing the fine, decade- to- decade record of the surface magnetic field back beyond the 1830s and finding out what high-speed changes like the one now occurring might mean for the immediate future. But this is just now changing: “archaeomagnetism,” one confined to snapshots derived from clay materials that were baked at some instant in the past, is using stalagmites to derive more detailed records of change over time, like those provided by the rings of a tree.
The magnetism experts mostly don’t think there is any immediate prospect of a total reversal of Earth’s magnetic field, and in the era of GPS the social importance of magnetic north is diminished — although not yet eliminated. GPS devices can be set to display magnetic bearings rather than truenorth ones; doing this, for example, allows militaries to co-ordinate between units navigating with magnetic compasses and ones that have GPS receivers. To do this, the devices have to have a recent version of the World Magnetic Model installed, even though the GPS system doesn’t make any use of the Earth’s magnetic field in establishing locations.
Airport runways are also still marked with magnetic headings, and the names of the runways sometimes need to be updated as the North Pole moves. A runway at a heading of 123º will typically be designated Runway 12, but the pole moves fast enough from decade to decade that the heading might easily become 127 º . With rounding to the nearest 10, Runway 12 must thus become Runway 13, necessitating an overnight frenzy of sign replacement, repainting of numbers on the tarmac, and editing of charts. I find it hard to believe this is really how things work, but it’s the sort of thing that happens when you try to reconcile human institutions with nature.