Cause of magnetic dip on Earth How is the magnetic dip (or inclination) caused on Earth?
 A: This is from Wikipedia and as you use the geomagnetism tag, I am not sure the comment mentioning the possible duplicate is correct, as it seems not to mention it.
If I have things backwards I will delete this "answer". (as it is just a cut and paste wikipedia copy).

Magnetic dip results from the tendency of a magnet to align itself with lines of force. As the Earth's magnetic lines of force are not parallel to the surface, the north end of a compass needle will point downward in the northern hemisphere (positive dip) or upward in the southern hemisphere (negative dip). The range of dip is from −90 degrees (at the South Magnetic Pole) to +90 degrees (at the North Magnetic Pole). Contour lines along which the dip measured at the Earth's surface is equal are referred to as isoclinic lines. The locus of the points having zero dip is called the magnetic equator or aclinic line.
  The phenomenon is especially important in aviation, as it causes the airplane's compass to give erroneous readings during banked turns and airspeed changes. The latter errors occur because the compass card tilts on its mount when under acceleration.[4]
  Compass needles are often weighted during manufacture to compensate for magnetic dip, so that they will balance roughly horizontally.


Illustration of magnetic field direction in a cross-section of Earth through its magnetic axis.

- From Press, F., and Sevier, R., 1998, Understanding Earth--2nd Edition: New York, W.H. Freeman via Rutgers.edu
A suitably suspended magnet orients itself to align with the magnetic field.

- From Marshak, S., 2001, Earth: Portrait of a Planet: New York, W.W. Norton. via Rutgers.edu
