From The New Republic:
The conceit this time out–not that it matters in the slightest–is that a series of escalating solar flares has produced a “mutated” form of neutrinos, which are penetrating the Earth’s crust and heating up its core. The ancient Mayans somehow foretold that this solar calamity would take place in 2012, but the movie makes no effort to explain how they knew: Emmerich’s in this for the earthquakes and super-volcanoes; leave the geo- and metaphysics to someone who cares.
Wow. To quote a physicist friend of mine, that’s not even wrong.