The only plausible scenario that remains possible is a polar shift, imo. The north pole has been accelerating rapidly over the past 10 years which is a good indicator that a polar shift might take place. Also, the winter solstice is a prime candidate for a polar shift instigation since the earth will be at the furthest point from the sun (staying there for 3 days, which is coincidentally supposed to be the length of a polar shift). Just food for thought.
I like to keep an open mind until something is 100% proven wrong, otherwise it's just ignorant to rule anything out ;) By all means though, I'd love to be proven wrong!
Proofs:
http://en.wikipedia.org/wiki/North_Magnetic_PoleEarth's magnetic field:

(^ It's supposed to be uniform)