[aceriscoolon]

> Could the Earth lose its magnetic field?

Not in the near future. A magnetic flip only affects the dipole component of the magnetic field. Higher order components such as quadrupole would still be around, and that would still give us plenty of protection against external radiation.

> Is our magnetic field already in decay?

Yes.

> The infamous South Atlantic Anomaly region exists in a weakened part of our magnetic field...Is this a forerunner of things to come?

Yes.

> When are we due for the next pole flip?

Nobody knows for sure. The pole positions have been constant for 780,000 years whereas the average time between flips over the past 5 million years is only 210,000 years. Also, that 780,000 years is longer than any other interval between pole flips in the past 5 million years, so in that sense we're overdue for a flip.

On the other hand, look at this image of the strength of the earth's magnetic field over the past 800,000 years. A value of "0" represents a flip. The Earth's magnetic field is actually stronger now (in the past 5,000 years) than it has been over any other time in the past 800,000 years so a flip looks unlikely in the near future. It looks as if at least another 20,000 years will occur before the next flip.



NASA’s Radiation Belt Storm Probes (RBSP) mission will probe the rate of weakening in detail and sort out differences between magnetic effects due to Earth's core and those due to the solar sunspot cycle.

> Will this contribute to a decay in our magnetic field?

Other way around. The decay in the magnetic field may or may not lead to a flip.

> Do any of the above present a greater danger to our fart arse little blue orb then say getting slammed by a large Asteroid, .....or human induced global warming?.

My preferred high risk danger is flood basalt. One is due about now and that would be about a million times as deadly as a magnetic reversal. Flood basalt is about 5 to 10 times the risk from an asteroid/comet impact. A star passing through the solar system (eg. Gliese 710 is due in 1.4 million years) and a nearby supernova are other dangers to watch out for. Global warming is more deadly than a magnetic reversal, but nowhere near as deadly as an asteroid/comet impact or flood-basalt/supervolcano event.

Of course, mass deaths due to economic collapse are just around the corner, unless nuclear war gets us first.

> Would rapid decay of our magnetic field contribute to global warming....

Not much - or would it? No, it wouldn't.

> Our magnetic field is thought to be caused by the differential spin rate, of the Earth's molten core and crust and mantle and convection currents created due to temperature differentials with depth. What would need to change with these physical aspects to affect the magnetic field to any great extent......

Time. The Earth's liquid outer core is slowly shrinking and freezing solid as the radioactive elements uranium and thorium decay. It is only the radioactivity of these elements that are keeping the outer core molten.

> Are we aware of when any of the situations I have mentioned are due?

Not that I know of.

> If not what sort of warning would we get [if we havn't got it already]

There are geomagnetic observatories set up all around the world to measure the long term variation in the Earth's magnetic field. Many of these were set up hundreds of years ago at about the same time as the first meteorological observatories. A website http://www.intermagnet.org/Welcom_e.php. The following is a map of magnetic observatories around the world.



> Are we confident of changes affecting our magnetic field to be a couple of billion years away?

For complete freezing of the Earth's outer core leading to permanent and almost total loss of the magnetic field. Yes.

> A few hundred thousand years?

For the next polar reversal at roughly that time.

> A few hundred years?

Some predictions for the next reversal are on that timescale, based on the strengthening of the South Antarctic Anomaly.