Earth's Magnetic Field Weakens 10 Percent

caryw writes "Interesting story from the AP. 'The strength of the Earth's magnetic field has decreased 10 percent over the past 150 years, raising the remote possibility that it may collapse and later reverse, flipping the planet's poles for the first time in nearly a million years, scientists said Thursday. At that rate of decline, the field could vanish altogether in 1,500 to 2,000 years, said Jeremy Bloxham of Harvard University. Hundreds of years could pass before a flip-flopped field returned to where it was 780,000 years ago. But scientists at a meeting of the American Geophysical Union cautioned that scenario is an unlikely one. "The chances are it will not," Bloxham said. "Reversals are a rare event."'"

Comments

Ummm...

[Anonymous Coward]

"The weakening -- if coupled with a subsequently large influx of radiation in the form of protons streaming from the sun -- can also affect the chemistry of the atmosphere, said Charles Jackman of NASA (news - web sites)'s Goddard Space Flight Center.

That can lead to significant but temporary losses of atmospheric ozone, he said.

Ozone Holes??

Re:This was on NOVA a week or two ago

[dgodwin]

I didn't think it was too "alarmist" as towards the end they talk about the only major negative effects of a weakened magnetic field and eventual switch is a slight increase in cancer (compared with all the cancer in the world as we know it today.) It also presented the possibility of having more than 2 poles, and a positive effect of the was having the auroras being visible all over the Earth. I showed this in my Earth Science classes this weeek, as we just started talking about how magnetic reversals are recorded in igneous rock, and is one of the pieces of evidence for sea floor spreading and plate tectonic theory.

Pointless estimation?

[barakn]

At that rate of decline, the field could vanish altogether in 1,500 to 2,000 years, said Jeremy Bloxham of Harvard University. Hundreds of years could pass before a flip-flopped field returned to where it was 780,000 years ago.

As I recall from the Nova program, a field reversal was essentially caught in the act by a single layer of lava. The interior of the lava flow had frozen in it a magnetic field 6 degrees different from the field frozen in the top and bottom of the flow, which cool faster due to contact with the atmosphere and the ground. This happened in a short period of time (days or weeks?). So saying "at that rate of decline" is pointless, as the rate of change would probably increase during a reversal. To illustrate, I'd like to point out that the north magnetic pole has been migrating further north at an accelerating pace. Although the link's text claims the acceleration occurred around 1970, their map shows it started sometime between 1904 and 1948, with perhaps a brief deceleration in the '60s.

And the sun is becoming more active at the same time. Things could get quite interesting on our little planet.

Re:rare? maybe, but

[GeoGreg]

Maybe. Many natural events can be modeled quite well as random variables following a particular distribution. I don't know whether magnetic field reversals follow such a pattern. However, the rate of reversals has varied significantly with time. For instance, there was a 37 million year period of stability during the Cretaceous period. More recently, the time between reversals has varied from less than one million to around 5 million years. And reversals in the mid- to late-Jurrasic were more frequent than any time since. (see this link).

The mechanism behind magnetic field reversals is poorly understood. I haven't seen any statistical analysis, but I would be interested to know if magnetic field reversals can best be modeled as periodic or as random, with some sort of variation about an expected value. It may be more accurate to say that the probablility of a reversal in any given year is increasing, rather than saying we are "overdue". Or maybe that is just splitting hairs.