Bushwalk Australia

Hey all, youve probably heard that some time (in the next hundred years or so) earths magentic field will flip over. This is nothing new, but does anyone know what kind of affect this might have on compasses? Would it simply mean north =south or perhaps accuracy would be totally shot? Curious about this

It's not likely it will happen in the next hundred years but it will happen again. The compass needle will still point somewhere so as long as declination tables on maps appropriately account for this there won't be a problem. Of course, by the time it happens it is not likely many people will use a compass for any serious purpose, few do now.

perfectlydark wrote: ... earths magentic (sic) field will flip over.

I’m not sure ‘flip’ is quite the right word (nor magentic, for that matter - rose coloured glasses??

Magnetic reversals occur randomly, any where between a few hundred and 1 million years (or more). The last one was around 800,000 years ago (although there was a brief 450yr reversal just 40,000 years ago) so, statistically, one is overdue – the average duration being half a million years.

It’s generally thought that the reversals take centuries to occur but some fairly recent evidence suggests that reversals can be very fast (eg 6deg a day = a month for a full reversal : pretty close to a flip) and very erratic.

A magnetic compass would be useless (even on a day to day basis) as many moving ‘poles’ would exist until the stability of the molten core (the cause of the magnetic field) returned.

The evidence (in lava flows and mid-ocean ridge bands) indicates that the Earth’s magnetic field doesn’t disappear completely (a good thing, because the magnetic fields limits the penetration of cosmic rays and the loss of atmosphere to space) but the strength varies greatly during and after things settle down – either an increase or decrease in strength would seem to be possible.

Of greatest concern, however, is the potentially disastrous effect on the biosphere such a change will have. Firstly, the earth's magnetic field performs a critical role in shielding the surface from solar wind - the highly energetic, charged particles that are drawn towards the poles, causing the well known aurora and Borealis, or northern lights. A change in the position of poles over time will almost certainly have dramatic effects on human health, communications (read satellites and internet), probably electricity grids, and quite possibly world weather/climate.

The second problem could be the navigation and migratory abilities of many animals, especially birds, possibly fish, maybe insects (bees?) who may use magnetic information as cues. The resultant disruption of ecosystems, particularly for farmers, could be catastrophic for human populations.

Of course, much of this is conjecture, I doubt if there's much modelling around. I just hope, like oversized meteorites and massive bird-flu pandemics, it doesn't happen in my, or my kids', lifetime.

Skibug

Excellent. With a drop in the magnetic field and greater solar radiation landing on the surface of Earth, expect more mutations and the next significant evolutionary step...

It is certainly an interesting subject. We're severely overdue, so it is more likely than unlikely to happen in our lifetimes. But, one could never know. We'll be flying blind, as we have mostly only educated predictions on its effects.

There have been numerous geomagnetc reversals over the ages and life goes on. The most recent one was as recent as 41,000 years ago and lasted 440 years. They are not such a big deal.

https://en.wikipedia.org/wiki/Geomagnetic_reversal

David M wrote:There have been numerous geomagnetc reversals over the ages and life goes on. The most recent one was as recent as 41,000 years ago and lasted 440 years. They are not such a big deal.

https://en.wikipedia.org/wiki/Geomagnetic_reversal

The issue is however how the technology we now depend on will be affected, and how that will impact daily life in the short and long term.

Jaala wrote: more likely than unlikely to happen in our lifetimes.

So you are saying that the likelyhood of a pole reversal in the next 90 years is greater than 50%?
What are you basing that on other than gut feel?


EDIT: Read the wiki http://en.wikipedia.org/wiki/Geomagneti ... _reversals

No, what I'm saying is that because we know they are a regular occurance on this planet and because it is deemed 'overdue' that the likelyhood of it occuring in the present time is greater than it was 100 years ago, 200 years ago, 30 thousand years ago. As time progresses the probability increases.

But the probability is so small that a slight increase means absolutly nothing in any realistic interpretation.

If that's the case, then the probability in 10,000 years is slim also. Interpretation and probability are two different things.

I'm not a statistician/actuary so I invite all who have been so trained to correct me here:

As far as I understand it's currently thought that geomagnetical reversal periods follow a levy distribution.
What this actually means is that:
the average period is infinite,
the likelyhood of large periods is underestimated by simple modelling.

An average period is not infinite if events have been defined with some regularity, average periods are a concept of man. That's not to say that such events must occur within a period, but make the probability they will occur more likely based on the data we have. Probability in the context of present vs past vs future is exactly that. +- If you're expecting an event that based on your experience/observations/data is an event that is due based on that experience/observations/data that event is more likely than unlikely and continues to be, based on this, more probable. It's all relative. A percentage of probability is useless in such regard.

Jaala wrote:

David M wrote:There have been numerous geomagnetc reversals over the ages and life goes on. The most recent one was as recent as 41,000 years ago and lasted 440 years. They are not such a big deal.

https://en.wikipedia.org/wiki/Geomagnetic_reversal

The issue is however how the technology we now depend on will be affected, and how that will impact daily life in the short and long term.

yes this is what im interested in. There were no electrical communicatioms 40k years ago, let alone compasses