Surprisingly rapid magnetic field reversals pose risks to Earth

A representation of Earth’s magnetic field shows how it extends from the poles in a protective embrace. A stalagmite from a cave in southwestern China holds telltale evidence of a surprisingly fast pole reversal some 98,000 years ago. Image: Peter Reid/NASA

Earth’s magnetic field, which shields the planet from solar radiation, periodically reverses, with magnetic south becoming magnetic north and vice versa. Such field reversals were thought to occur over thousands of years, but new research shows at least one happened in just two centuries or so when the magnetic field’s strength was reduced by 90 percent.

Such an event in today’s electronically interconnected world could cost trillions in damage to power and communications systems, the researchers say, while exposing the biosphere to increased levels of solar radiation.

“Earth’s magnetic field, which has existed for at least 3.45 billion years, provides a shield from the direct impact of solar radiation,” said Andrew Roberts of the Australian National University’s Research School of Earth Sciences. “Even with Earth’s strong magnetic field today, we’re still susceptible to solar storms that can damage our electricity-based society.”

Roberts and a team of researchers led by Chuan-Chou Shen at the National Taiwan University and lead author Dr Yu-Min Chou of the Southern University of Science and Technology in China carried out precise radiometric dating of a stalagmite from a cave in southwestern China that recorded paleomagnetic changes dating from 107,000 to 91,000 years ago.

The team noted evidence for field reversals that occurred over a few centuries to several thousand years “indicating prolonged geodynamo instability.”

“One surprisingly abrupt centennial reversal transition occurred in 144 ± 58 years and provides unprecedented evidence that raises fundamental questions about the speed of geomagnetic field shifts,” notes an introduction to the paper in the Proceedings of the National Academy of Sciences of the United States.

“Such rapid polarity changes could severely affect satellites and human society in the future if the current geomagnetic field intensity continues to decrease.”