This article is from last year but still has some very pertinent pointers...

When scientists mapped the Earth's magnetic field down to the level of the outer-core, they discovered that under the South Atlantic Anomaly the simple north-south divide we know at the surface had broken down. There are patches where the field has actually flipped and points north instead of south.

[link to www.bbc.co.uk]

If these patches continue to deepen and spread, the entire Earth's magnetic field could reach a tipping point and flip, he believes.

edit to include:

[link to www.astronoo.com]