There are no scientists who think that there will be a magnetic pole reversal in 2012.
When I was studying magnetism a few decades ago, we knew that some signs of upcoming reversal were "upon us" (the field has been weakening, the pole's surface location is wandering, the south magnetic pole had split).
We were so sure that some of us were willing to bet that it could be as early as the year 3500.
More recent observations have confirmed that the wandering of the poles is increasing. Now, just about every scientist who studies Earth's magnetism is willing to accept that it could be around the year 3500 (give or take a century or two).
By observing traces of magnetism in layers that can be dated (for example, lava flows from volcanoes), we find that magnetic reversals occur on average every 700,000 years (but the cycle is not very regular), and that the reversal process takes an average of 5000 years (although one reversal took "only" 1,000 years).
So, some scientists want to be bold and say that the reversal could be in the early part of the 4th millennium and could be over by the early part of the 5th millennium.
Most of them now agree that the "flip" could be over by the year 8500. I will try to stick around to see who is correct.
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Beware of the fallacies about 2012 (even if they are shown on the History Channel):
The Mayan calendar does not end, it only reaches a round figure (this is exactly the same as our calendar reaching the year 2000, a round figure).
The Mayans did not predict the end-of-the-world. In fact, the Mayans use their calendar to date events (involving humans) that they thought will happen on Earth after the year we call 4000.
The Earth (or the Sun) cannot line up with the Galactic centre. Ever.
The closest it comes is still a little more than 5.5 degrees. It has been doing so every year (twice a year) at the dates of the solstices. It will continue to be like that for a few centuries.
Nostradamus never wrote anything about 2012. In fact, he never wrote anything that applied after the end of the 16th century (1600).
The people who invented the 2012 end-of-the-world are NOT the same people who gave us Y2k. However, many of the fake predictions about 2012 come from the same people who had "predicted" the end-of-the-world in 2003 (with Planet X). But even they did not pick the date. This was done by José who claims to understand the Mayan calendar.