He writes:

The magnetic field deflects a lot of the Sun’s incredibly nasty radiation, so if you take it away, we could all get microwaved to a crisp.

Even scarier: The Earth's magnetic field has weakened by ten percent over the last 160 years. Does that mean we're due for a flip? Dan Lathrop, a geophysicist at University of Maryland, will try to find out when he spins up his mega steel ball and recreates (on a small scale) the magnetic conditions on Earth. [via Collision Detection]

The Sun is obviously the biggest reason we're alive today — without it Earth would be a lifeless, frozen lump of rock at best. The same is probably true of the oceans, Earth's distance from the Sun, and so on. But Earth's magnetic field doesn't get enough credit (apart from a few terrible movies like "The Core") as being just as important as any of those ingredients for keeping life on Earth. Without it, highly energetic particles from the Sun would fry life, shatter life-giving molecules floating in the air and water, and strip away most of our atmosphere (witness Mars, whose thin atmosphere has been ravaged by solar winds).

In just a few centuries that may be a reality. Even if the field doesn't disappear entirely, in a weakened state it could let enough radiation in to cook the vast communications networks and power girds that have sprung up around the planet in the last century. But searching through ancient copper mines in Israel and Jordan has turned up some interesting new evidence. By looking at layers of metal slag that aligned themselves based on the magnetic field that was present as they cooled thousands of years ago, scientists at Scripps Institute of Oceanography and UC San Diego have managed to reconstruct the field's strength. What they found was startling: about 2,000 years ago Earth's magnetic field peaked in strength, and it's been weakening ever since.

The field itself isn't going away any time soon — it's powered by oceans of molten metal churning at the center of the planet — but for reasons we don't quite understand, every quarter million years or so it reverses polarity. Each time it does this, there's a period of a few days to a few hundred years where the field becomes so weak that it's almost non-existent, and that's what we seem to be heading for.

What does this mean for life on Earth? Bottom line is we don't know. Some scientists have argued that mass extinctions line up with field reversals in Earth's past, while others say that when the field flips it flips too fast — maybe over the course of a week or less — to do anything more than cause a glitch in your cell phone reception.
The one thing we can take comfort in is that the decline has so far been slow and steady, so humans alive today probably won't have to worry much.

But our fuzzy understanding from the geologic past suggests that as the field weakens further, it's polarity can wander all over the place, flopping back and forth like a fish out of water. If that's true, in a couple of generations global warming from CO2 in the atmosphere might be the least of our worries.

Source: Scripps Institute of Oceanography

Using the Extreme-Ultraviolet Imaging Spectrograph mounted on the Hinode spacecraft, astronomers pinpointed the pressure fluctuations in the immense magnetic fields that send the gases spewing out into the sun's corona. In a press release, Dr. Michelle Murray of the Mullard Space Science Laboratory at University College London had this to say:

When a new section of magnetic field pushes through the solar surface it generates a continual cycle of fountains, but new magnetic fields are constantly emerging across the whole of the solar surface and so our results can explain a whole multitude of fountains that have been observed with Hinode.

New Views On The Sun's Startling Magnetic Fountains. [Science Daily]