Reduction of the Earth's magnetic field

QUESTION: What will happen when the magnetic field of the Earth reaches its minimum value or it becomes zero? What will be the effect on the atmosphere and vegetation?

Answer

If the magnetic field of the Earth fell to zero it would expose the surface to cosmic radiation - especially the charged particles of the solar wind which are normally deflected by this magnetic field.

I don't believe that there would be any substantial effect on the atmosphere except for the occurrence of auroras at many places on the globe. (Northern Lights – glows in the atmosphere as the particles descend). At present this is only observable at high latitudes.

Because of the absorbing affect of the atmosphere most of these charged particles would be absorbed before they reached the ground and so would have little effect on the vegetation.