: There is evidence in deepearth holes bores that the magnetic poles switch on a periodic basis. Not sure but I seem to recll it happening every 20,00 years and that we are due for one within a thousand years.

A quick search on the web reveals that I am off by only a factor of 20. The poles reverse every half million years with the last one occurring 700,000 years ago. So we are overdue. Read for yuorself at http://www-spof.gsfc.nasa.gov/Education/FAQ.html#q1