The great disasters of the "galactic alignment" in 2012 were supposed to have occurred on December 21st, the day of the solstice. The filmmakers decided to move those events up a few months, to midsummer. This relieved them of having to decorate the sets for the winter holidays.
The film was banned in North Korea because 2012 marks the 100th anniversary of the birth of First Great Leader Il-Sung Kim. Several people were arrested for watching pirated copies of the film.
When Jackson rents a plane, he gives the pilot his watch as payment. He tells the pilot that it was given to him by his editor when he thought he was going to be someone, and that it's worth something. The watch is a Classic Pilot Mark XVI, and sells for at least $3,000.
The doomsday theory arose from a non-Maya Western idea, not a Mayan one. Mayas insisted that the world would not end in 2012. The Mayas had a talent for astronomy, and enthusiasts found a series of astronomical alignments they said coincided in 2012. Once every 640,000 years, the sun lines up with the center of the Milky Way galaxy on the winter solstice, the sun's lowest point in the horizon. The last time that happened was on December 21, 2012, the same day the Maya calendar expired. The modern doomsday myth was bolstered by several ostensibly scientific reasons for a disaster, including a pole shift, the "return" of Planet X or the Sun's sinister counterpart Nemesis, a galactic, planetary, or other celestial alignment, global warming, global cooling, a massive solar flare, or a new ice age. None had any basis in real science. For example, the "galactic alignment" between the sun, Earth, and galactic center happens every December. The best alignment was reached in the 1990s, and was accompanied by its own set of doomsday theories. Alignments since then have been increasingly poor.
The character of Charlie Frost seems loosely based on volcanologists David Johnston and Harry Glicken. Johnston was killed in the eruption of Mount St. Helens in 1980. He was able to broadcast, "Vancouver! Vancouver! This is it!" as a warning before he died. Glicken was killed by a pyroclastic flow on Mount Unzen in Japan in 1991. He was so eccentric and disorganized that the U.S. Geological Survey only offered him temporary positions, despite his incredibly thorough research on Mount St. Helens.