The apocalyptic possibilities of planet alignment in 2012 are both 'possible' and 'not possible.'
The Earth has ALWAYS suffered cataclysmic occurences that appear to have, on a regular basis, returned the human race to its fragile beginnings in technology.
Planet alignment may and may not cause the Earth Crust to shift cataclysmically, literally causing mass Earth quakes and altering our magnetic pole. Then again it may not. We do not know what gravitational forces may come into play when the planets align, all we do know is that it is very likely than the Earth's Poles have shifted before with apocalyptic results. (Charles Hapgood's 'The Path of the Pole' is a theory that Albert Einstein agreed with.)
Perhaps we return to the stoneage technology after 2012 if the masses of humanity are killed and few survive. Then again, perhaps nothing at all will happen. We will have to wait and see. The one thing that IS certain, is that the Earth is already changing climate, and only part of it is caused by us. We are basically just accelerating natural changes.
Change is afoot! How big a change....we are soon to find out.