QotW: What happens if Earth's polarity flips?

What happens if the Earth's magnetic field ever reverses its polarity? Geologist John Underhill explains...
24 January 2020


A picture of the Earth from the ISS space station



"My question relates to the reversal of the Earth's magnetic field. The Earth has apparently reversed its polarity fairly regularly, and is perhaps overdue for its next instance. Is anything known about how this will happen, and the effects? Will it be quick or slow? Will the Earth's magnetic field be reduced for a period of time, leaving us open to solar radiation and perhaps other effects? How will it effect our reliance on technology?"


We got this Earth-shattering question from listener Ray. Megan McGregor sought out the answer, with help from geologist John Underhill...

Megan - The Earth’s magnetic field is generated by the swirling motion of liquid iron metal in our planet’s core. This magnetic field is approximately the same shape as the field around a bar magnet, with one north and one south pole - a so-called dipole field. I talked to Richard Harrison, Head of the Department of Earth Sciences at the University of Cambridge, to find out how long the field might take to flip.

Richard - Every 200 to 300 thousand years on average, the polarity of the Earth’s field flips round, so what was the magnetic north pole becomes the magnetic south pole, and vice versa. The last reversal was 780,000 years ago, so yes, you could say we are ‘overdue’ for a reversal. However, reversals occurs randomly and at irregular intervals, so it is impossible to predict exactly when the next one will occur, and although some aspects of  the field can vary quite quickly (on the order of 10s to 100s of years) a full reversal takes a few thousand years to complete, so even if were to begin tomorrow it would not flip in our lifetime.

Megan - It’s a classic disaster movie plot: the earth’s magnetic field reverses suddenly, and all hell breaks loose. Richard suggests reality might not be quite so apocalyptic.

Richard - To understand what a reversal might look like it crucial to realise that the magnetic field is not a perfect dipole. For example, in the South Atlantic Anomaly - a region of unusually low magnetic field strength in the South Atlantic – the field deviates significantly from that of the expected dipole field.

Megan -  During a reversal the regular dipole part of Earth’s magnetic field would be zero, leaving only these strange anomalies behind. We could end up with more than just two magnetic poles, spread around the world.

Richard - In this multipolar state, the magnetic field is significantly weaker and more complex, leaving us more exposed to the influx of cosmic rays and solar irradiation. The effects of this would be similar to those currently experienced inside South Atlantic Anomaly: satellites suffer increased interference as they pass through that region, and astronauts have reported their laptops crashing. On Earth we could see massive disruption to power and satellite communication networks, as well as increased exposure to cosmic rays, which experiments have shown could lead to cognitive dysfunction. Having said that, the field has flipped many many times during Earth’s past, with little evidence that it has had a major impact on life - we’d probably survive but our mobile phone reception may not…

Megan - Thank you Richard. Next week’s burning question comes from Robin.

Robin - I heard in the podcast that the reason why we get a sunburn is that the body is trying to fix cells that are damaged by UV radiation. So if one person is sunburned longer than another, does that mean their immune system is worse?


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