Earth’s Magnetic Poles, Reversing or Not?

Among the many doomsday speculations for the year 2012 is concern that the Earth’s magnetic poles are beginning to reverse polarity and the event would have dire consequences should it occur. The Earth’s magnetic field helps protect us from cosmic ray radiation. Such speculation is unfounded. The magnetic poles have switched many times, apparently at random intervals. See leftmost column of geologic times scale here. The black and white stripes show the timing and duration of polar reversals.  The last time the polarity reversed was 780,000 years ago.

Mid ocean ridge magneticsWe know when these reversals occurred because magnetic polarity direction is recorded in the rocks. At mid-oceanic ridges, fresh magma reaches the surface and spreads out. Magnetic minerals align with the magnetic polarity existing at the time and are locked in as the magma solidifies. (Diagram from NASA).

The Earth’s magnetic field is produced by the interaction of the Earth’s solid iron core with the liquid outer core. The inner core spins slightly faster than the earth rotates on its axis. The spin sets up convection and eddies in the liquid core just like the spin of the Earth produces currents in the oceans and atmosphere. However, the exact mechanism is still subject to controversy, but most hypotheses are variations of the dynamo effect.

Earth dynamoThe Earth’s magnetic field varies in intensity because of these eddies and because the axis of rotation of the core is not the same as the axis of rotation of the Earth. That means the north magnetic pole is not in the same location as the geographic north pole. In fact, the magnetic poles wander and even vary in location on a daily basis by as much as 50 miles according to the Geological Survey of Canada, the folks who keep track of where the pole is.

The magnetic poles also have a longer-term positional change. Currently the average position of the north magnetic pole is heading out of Canada toward Siberia at the rate of 25 miles per year. See this page from the Geological Survey of Canada for details on North Pole wandering, and this page for both north and south pole locations.

Some of the concern about an imminent magnetic reversal derives from the fact that the strength of the magnetic field has been decreasing for the last 100 years. But fluctuations in intensity are common. The current strength of the magnetic field is nearly twice as high as the average for the past 2 million years, see graph below (source). The jump was at the last reversal.

Earth magnetic field strength

But what could happen during a reversal? First, reversals take several thousand years. The magnetic field does not become zero, but even if it did, the sun’s magnetic field would protect us. (By the way, the sun switches magnetic polarity every 9- to 12 years.)

According to University of California professor Gary Glatzmaier, during a magnetic reversal, the magnetic force does not go to zero; it becomes complicated. Glatzmaier used a super computer to model what might happen, see graphic below.

Earth magnetic life during reversal

We note that there have been many magnetic reversals and there is no evidence that it had a profound affect on life. Humans and humanoids have been through several reversals. Because the reversal process occurs over thousands of years, animals, such as birds, and whales, that may rely on magnetic navigation would have time to adapt.

Some of our own navigation and surveying systems depend on keeping track of where magnetic north (or south) is. Fortunately there is an app for that. This NOAA calculator allows you to get the constantly changing magnetic declination from true north at any location.

In Tucson, a magnetic compass points 10 degrees, 29 minutes east of true north. But that declination is decreasing by 6 minutes per year.

A magnetic reversal in 2012, or any time soon, is unlikely. But the process has occurred at random intervals in the past and is still poorly understood.

UPDATE: Why the pole is speeding toward Russia:

The north magnetic pole (NMP) has been drifting in a north-northwesterly direction since the 19th century. Both local surveys and geomagnetic models derived from observatory and satellite data show that the NMP suddenly accelerated during the 1990s. Its speed increased from about 15 km/yr in 1989 to about 60 km/yr in 2002, after which it started to decrease slightly. Using a Green’s function, we show that this acceleration is mainly caused by a large, negative secular variation change in the radial magnetic field at the core surface, under the New Siberian Islands. This change occurs in a region of the core surface where there is a pair of secular variation patches of opposite polarities, which we suggest could be the signature of a so-called “polar magnetic upwelling” of the type observed in some recent numerical dynamo simulations. Indeed, a local analysis of the radial secular variation and magnetic field gradient suggests that the secular variation change under the New Siberian Islands is likely to be accompanied by a significant amount of magnetic diffusion, in agreement with such a mechanism. We thus hypothesize that the negative secular variation change under the New Siberian Islands that produced the NMP acceleration could result from a slowdown of the polar magnetic upwelling during the 1990s. We finally note that the NMP drift speed is determined by such a combination of factors that it is at present not possible to forecast its future evolution.





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