Lopsided growth of the Earth’s core could explain why its magnetic field reverses direction every few hundred thousand years. If it happened now, we would be exposed to solar winds capable of knocking out global communications and power grids.

One side of Earth’s solid inner core grows slightly while the other half melts. Peter Olson and Renaud Deguen of Johns Hopkins University in Baltimore, Maryland, used numerical modelling to establish that the axis of Earth’s magnetic field lies in the growing hemisphere – a finding that suggests shifts in the field are connected to growth of the inner core.

There are signs that the next switch may be under way: rapid movements of the field’s axis to the east in the last few hundred years may be a precursor to the north and south poles trading places, the researchers speculate.

“What we found that is interesting in our models is a correlation between these transient [shifts] and reversals [of Earth’s magnetic field],” says Olson. “We kind of speculate there is that connection but the chaos in the core is going to prevent us from making accurate predictions for a long time.”


Bruce Buffett of the University of California, Berkeley, says the authors present an intriguing proof of concept with their model.

“They are suggesting very cautiously that maybe this rapid change is somehow suggestive of us going into a reversal event,” he says. “You could imagine if the field were to collapse it would have disastrous consequences for communication systems and power grids.”

Journal reference: Nature Geoscience, DOI: 10.1038/ngeo1506

Correction:This article has been updated to correct the frequency with which the north and south poles of Earth’s magnetic field swap places.