In the 2003 movie The Core Earth’s molten core stops spinning, which causes the planet’s magnetic field to fail and disaster ensues. A team of brilliant scientists (played by some good actors like Aaron Eckhart and Hilary Swank) uses a giant burrowing machine to drill down to the core and explode nuclear warheads to restart the circulation. It’s a plot you’d expect from a 1950’s B-movie, and that’s probably why I like it, but it’s generally considered a ‘guilty pleasure’ movie at best. Still, it got some things right. A weakening of our magnetic field could leave our electronics-based civilization frighteningly vulnerable, and threaten most life on Earth. A complete loss would be disastrous. And some scientists are raising the alarm.
Maybe you did experiments with magnets and iron filings in school, or maybe you’ve just seen drawings of a magnetic field—curved lines around the magnet that curl in and touch the positive and negative poles at each end. In Earth’s case, the north and south poles. Our planet is like a ball in the middle of a giant invisible doughnut. Without that field, we couldn’t live here, and it may be in danger of collapse.
It isn’t because the Earth’s core has shown signs of stopping. No, the concern comes from the fact that we know from geological records (indicators in ancient rock) that the magnetic field has switched poles pretty often during Earth’s history. North becomes South and the magnetic flow reverses. Though the time between such flips varies a lot, it’s averaged about every 200,000 to 300,000 years, and it’s been 780,000 years since the last one so some scientists say we’re overdue.
So what’s the big deal? Your compass reads north when you’re facing south, and some migratory birds get confused? Sure, but it’s what happens during the transition that’s the problem. You guessed it: the magnetic field is significantly weakened—possibly reduced to as little as ten percent of its usual strength at times. And the pole reversal isn’t quick, like flicking a switch. Indications from rock layers show that it might take thousands of years. The unreliability of a compass heading will be the least of our worries.
What makes the Earth’s magnetic field so critical is that it protects the planet’s surface from a bombardment of high-energy particles from space that can wreck DNA in living organisms (causing mutations and cancers, or even quicker cell deaths) and overloads electric wiring and electronic circuitry. That bombardment is happening all the time, but it gets much worse when our sun has indigestion. Solar storms send out mammoth flares of high-energy X-rays and particles plus ionized gases that can really mess up our communications and power grids. A flare in March of 1989 knocked out power all across the Canadian province of Quebec, but it was much smaller than an event recorded back in 1859 when telegraph wires were first spreading over the continents. Known as the Carrington event, that one was so powerful that the northern lights were seen as far south as Tahiti and Cuba. Not only did overloaded equipment fail under the strain, many of the telegraph cables themselves caught fire! And that was with the planet’s protective magnetic field at full strength.
As recently as 2012 a solar storm at least as powerful as the 1859 event sprayed deadly energy out into space, but we dodged that bullet—the storm was on a part of the sun facing away from Earth. A week or ten days earlier, it would have hit us. Here's a good NASA video about the near miss and what could have happened. Now imagine if it had hit us when the magnetic poles had begun a reversal and the Earth’s shielding was at only ten percent of normal.
It’s not a pretty picture. Ionized particles would fry the circuitry of satellites. Magnetic induction would produce enormous amounts of electric current throughout our power grids, blowing transformers and other equipment everywhere exposed to the blast. And since we just don’t have huge numbers of spare transformers lying around, some analysts estimate our civilization could be knocked back to Victorian times.
That’s a worst case scenario raised in the recently published The Spinning Magnet by journalist Alanna Mitchell, and mentioned elsewhere. Others strenuously downplay the danger, although even they admit that we would do well to prepare for fluctuations in the strength of the magnetic field by fortifying our power grids and technological infrastructure.
Whether such a crisis is imminent or not, it sure provides fodder for some juicy disaster fiction! (But solid SF writers, please. Not Hollywood—they just don’t seem to know the difference between meaty and cheesy.)