Earth’s Magnetic Field Reversal: Should We Worry?
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Earth’s Magnetic Field Reversal: Should We Worry?

By Dr. Zoomie

G’day, Dr. Zooms – Hoping you can help me with something I read recently. It said that our magnetic field is going to go away and won’t be able to protect us from cosmic radiation. Is this going to be dangerous? Is it going to cause a lot of people and animals to die from radiation sickness? How worried should I be?

Well…not very much. One of the things my MS advisor told me was “Make sure you don’t prove that life can’t exist on Earth…because we’ve got a lot of evidence that it does.” The Earth has been through more than 180 magnetic field reversals in the last 83 million years alone – each of which involves the magnetic field vanishing for a time – yet life is still abundant on Earth. That tells me that we will safely navigate through the coming magnetic field reversal. Having said that, let’s talk about what’s going to happen and why it’s not a huge concern.

Earth’s magnetic field is strongest over the equator and weakest at the poles – this is why we see the Northern (and Southern) Lights, which are due to charged particles spiraling into the atmosphere at points where the magnetic field is weak. I’ve measured this radiation myself on some of my travels that took me over the Arctic – and I’ve also noticed that there’s plenty of life in Alaska and Northern Canada…and Siberia looks from the air to be pretty well filled with trees (you can’t see much more than that from 35,000 -40,000 feet). To put some numbers in there, cosmic radiation dose rate averages a tad less than 30 mrem annually, with dose at the poles about 20% higher than at the equator. Twenty percent of 30 mrem is about 6 mrem – that’s about what I measure in a single coast-to-coast flight in the US (NYC to LAX, for example). Losing our magnetic field for a relatively short period of time (a few centuries to a few millennia) isn’t going to increase radiation levels on Earth’s surface enough to make much of a difference to our health, and it certainly won’t kill us all – as the fossil record shows.

Much of the reason for this is that our atmosphere soaks up most of the cosmic radiation that makes it through the magnetic field, reducing the radiation dose by several orders of magnitude. Protons that make it through the magnetic field strike atoms in the air; some are absorbed by the nucleus, causing it to eject neutrons and other protons. In the short term, this isn’t going to cause problems – if the magnetic field is absent for a long enough time then this might be a concern. Having said that, magnetic field reversals are usually over within 5000-10,000 years while it takes millions upon millions of years to strip away an atmosphere, which is why, in spite of so many magnetic field reversals over the eons, Earth’s atmosphere remains intact.

See, the thing is that when cosmic radiation strikes atoms of the atmosphere, sometimes they knock the atoms out of the atmosphere and into space. Over a long enough time, cosmic radiation can deplete a planet of its air. Some think this might explain why Mars lost what appears to have been a reasonably dense atmosphere in its youth. Understand that this is not the sort of thing that happens overnight – it takes tens of millions of years. But, given enough time, if Earth loses its magnetic field, our atmosphere might evaporate into space in the (geologically) relatively near future. Which would be bad for us…or, rather, for our distant descendants some millions of years in the future.

Having said that, Venus, which is close to being Earth’s twin as far as mass and diameter go, has no magnetic field and its atmosphere is much thicker than what we have on Earth. So it might be that Mars lost its atmosphere as a result of having no magnetic field and having too little gravity – it might be that our higher gravity would let us hold onto our atmosphere even were our magnetic field to vanish forever. And then again…maybe not; there’s not enough information to know for sure.

If we look at the planets in our solar system we can see that Venus, Earth, Jupiter, Saturn, Uranus, Neptune, and Titan (a moon of Saturn) all have thick atmospheres; Mars and a few moons in the outer solar system have thin atmospheres, and none of the other bodies have an appreciable amount of atmosphere. All of the bodies with a thick atmosphere also have relatively strong magnetic fields, except for Venus. This suggests that Venus (and, by extension, Earth) might be just massive enough to hold onto its atmosphere even in the absence of a magnetic field. But with only one example, we don’t know if this is a general principle or just good luck.

One other thing that might happen if we lose our magnetic field is that solar storms might have more of an impact on our planet and our technology. In 1859 the Sun belched out a flare that ejected massive amounts of plasma into space; this plasma hit the Earth less than a day later, slicing through our planet’s magnetic field and slamming into our atmosphere – the Carrington Event. There, the protons and electrons caused more ionizations and those, in turn, generated huge electrical fields; these caused electrical currents to flow through telegraph wires and the surge of electrical current knocked out telegraph stations around the world and even caused fires in telegraph equipment. Not only that, but the electromagnetic forces unleashed by this event generated electrical current in the telegraph lines such that, even with their batteries disconnected (in those days before there was a power grid), telegraph operators were able to continue sending telegraphs for two hours or more. Such an event today would knock out electrical grids across our planet, affecting power systems, communications, computers, and everything that depends on them. And in the absence of our magnetic field, such events might become common. Our civilization might stagger, until we learn to harden our systems against these events, but humanity and the biosphere will survive.

Note: The image above is a computer simulation of the Earth’s field in a period of normal polarity between reversals. The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. Published by NASA in 2003 on their website, originally produced by Dr. Gary A. Glatzmaier – Los Alamos National Laboratory – U.S. Department of Energy.