the Magnetic Pole Shift

A geomagnetic reversal, which is sometimes called a “polar reversal” or a “pole shift”, is a change in the Earth’s magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth’s field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was in the opposite direction. These periods are called chrons. The time spans of chrons are randomly distributed with most being between 0.1 and 1 million years. Most reversals are estimated to take between 1,000 and 10,000 years. The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago.But brief disruptions that do not result in reversal are called geomagnetic excursions.
Now you might ask yourself; when will the next one occur.. 

Well according to an article by Scientific American (2002) which claims that
The reversal may have already begun

"Though the process can take nearly 5,000 years, the earth’s magnetic field periodically reverses. According to a report published today in Nature, scientists may have detected the beginning of the field’s next such reversal."