I was watching a program on Channel 4 yesterday called "Magnetic Flip"* yesterday, when Mr. Bsag wandered in some time after it had started.
Him: "Oh, so what's the looming disaster that will destroy the Earth this week?" Me: "We're going to lose the Earth's magnetic field, and then all our atmosphere and water will get blown away into space by the solar winds, and we'll all be very dry toast." Him: [Long pause] "Right. What do you want for dinner?"
If you've watched any science programmes at all on TV, you won't be surprised to learn that the whole 'atmosphere being blown away' thing was a bit of a device to get our attention. OK, so there is evidence that it happened to Mars, but the decline in the strength of our own magnetic field seems to have another cause: the polarity is about to flip. This is something that usually happens at fairly regular 200,000 year intervals, but as it's 700,000 years since the last flip, we're a bit overdue for one.
The evidence for this was rather fascinating, and unusually varied, including sampling of the magnetic polarity in ancient pottery and mountains, searching the meticulous Navy records of magnetic anomalies going back a couple of centuries, and computer models (which were very pretty). The coolest experiment involved igniting a spinning ball of 10kg of sodium inside a very complicated piece of apparatus, in order to try to model what goes on in the Earth's core. I have very exciting memories of what happens to a tiny pea-sized piece of sodium in water from chemistry lessons at school, so the thought of 10kg of sodium going up makes my eyes gleam.
In case you are still worrying about what will happen to us when all this flipping happens, here's the bad and good news. The bad news is that magnetic compasses are going to be next to useless for quite a long time. While the magnetic fields is doing all its swirling around and rearranging itself, the weaker field and multiple foci — where the field enters or exits the earth — will result in a greater level of cosmic radiation in inhabited areas. This will probably result in a higher incidence of cancers, but given that loads of other self-inflicted carcinogens will almost certainly increase, I'm not sure that we'll really notice the difference. The good news? Well, the auroras will be spectacular, and you won't have to freeze your ears off above the Arctic Circle to see them. Woo-hoo!
* I would post a link, but Channel 4 doesn't have any information up about this program.