Why would the North Magnetic Pole (dip pole) of the Earth be well-defined (uniquely determined)? Strongly inspired by the current thread Are there necessarily always at least two points where the Earth's magnetic field is vertical?, this is the opposite question:
Is there necessarily always at most one point (on Earth's surface) where the Earth's magnetic field is directed vertically downwards?
The English Wikipedia page North Magnetic Pole currently says:

The North Magnetic Pole is the point on the surface of Earth's Northern
  Hemisphere at which the planet's magnetic field points vertically downwards
  (in other words, if a magnetic compass needle is allowed to rotate about a
  horizontal axis, it will point straight down). There is only one location
  where this occurs, [...]

(emphasis mine).
Of course the Earth's true $B$ field is far from an exact dipole field, see e.g. these diagrams.
Can it not occur that there are two distinct magnetic poles in the Arctic, say separated by 100 kilometers, where the inclination is exactly +90 degrees?
Are there any geometric, electromagnetic or geophysical "laws" preventing that? I cannot think of any.
 A: If some fluctuation in the currents in Earth's core was to originate a second magnetic axis, the magnetic moments relative to the two fields (the "normal one" and the "anomalous one") would start to exert forces on each other until they merged in a single field, according to the equation for the torque acting on a magnetic dipole in an external field:
$$\vec \tau = \vec m \times \vec B$$
Therefore any fluctuation would be quickly suppressed by the forces exerted by the magnetic field itself. The only possible equilibrium situation is one in which there is only one magnetic axis.
In the picture below (source) you can see a simulation of the magnetic field of Earth in an equilibrium situation and during a geomagnetic reversal; blue lines represent outgoing field, and orange lines ingoing field. 
As you can see, during the reversal there are multiple "poles", but eventually the field returns to a dipolar one (but with a differently oriented magnetic axis).

A: Jeppe, as the images above show, there can be multiple "north" poles at the same time. However, I disagree with the stability analysis by valerio92. There is nothing about magnetic torques that favors a dipolar structure; just look at magnetic domains in ferromagnets.
There are two main reasons the Earth's field generally has two poles that are nearly aligned with the geographic poles: the Earth's rotation tends to organize the flow, and the solid inner core tends to slow down any changes, giving the rotation time to assert its influence. For more information, see this summary by the scientist who generated the images.
