Physics

Earth's Electromagnetic Field Is Weakening

June 21, 2014 | by Stephen Luntz

Photo credit: EST/DTU Changes in the Earth's magnetic field strength vary greatly across the planet.

The Earth's magnetic field, which protects us from radiation from space, is getting weaker. We don't yet know why this is, but new evidence confirms it is happening unevenly across the planet with some areas getting more protection.

Evidence of weakening of the magnetic field, and it's geographically inconsistent nature, has been tracked for decades, but the November 2013 launch of the European Space Agency's three satellite Swarm constellation has allowed unprecedented precision in measuring these changes.

The field is a result of the Earth's iron core acting as a giant magnet. However, the core is not stable, with the magnetic north and south poles wandering around at rates of around 15 km/year for most of last century, and recently accelerating. Over periods of millions of years the poles sometimes switch places, and there is some speculation that such a switch is coming soon.

The north magnetic pole is currently moving towards Siberia from its location in Canada.

The field averages a strength of around 40,000nT, so even the loss of 80nT over North America (see above) is small. However, this is in a period of just six months – should the trend continue for long enough the effects could eventually become serious. A weaker magnetic field would expose the planet to increased radiation, both from distant supernovae and from the solar events, although there is no evidence that the doomsday scenario of a planet temporarily without any magnetic field at all has ever occurred. 

EST/DTU Magnetic field strength across the planet June 2014

A polarity flip, or drastic weakening would not be lethal, as demonstrated by the fact that past changes have not been associated with mass extinctions, but could expose powerlines and communication systems to much greater danger. On the positive side, auroras should become more spectacular and widespread. Should such an event occur, most scientists anticipate the timescale will be of the order of millennia, rather than decades, making the Daily Mail's call to “forget global warming and start worrying about the Earth's magnetic field” typically stupid.

The changes are driven by a complex set of sources, from the core, mantle and crust of the Earth and influences in space. The largest influence is thought to be the convection currents in the molten iron of the core causing expansion at some points and contraction at others. Thee convection currents may sometimes lead to domains where the magnetic field runs in the opposite direction to the main field, canceling part of it out.

The results were presented at the Third Swarm Science Meeting, held in Copenhagen on Thursday. The Swarm Mission Manager Dr Rune Floberghagen said, "These initial results demonstrate the excellent performance of Swarm. With unprecedented resolution, the data also exhibit Swarm's capability to map fine-scale features of the magnetic field."

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