Plot hole: During the later parts of this movie there is much talk about 'continental displacement' and this appears to be happening in the film. The Earth's crust is falling apart because of the heating of the inner core, and all the cities seems to be falling apart since the ground can no longer hold them. When our cast finds themselves surprised to be already over China when they figured to be over the ocean, it is explained that Asia has actually moved from where it was. If this phenomenon is taking place globally, how come the monks in China don't seem to have been disturbed at all? In fact the bell the monk rings as the ocean approaches hasn't even been shaken. The arks are built in between the mountains, but the mountains are apparently fine. Shouldn't they be falling like the rest of the crust?
Plot hole: Given the amount of destruction all over the world, it is HIGHLY unlikely the use of phones by general public would be possible, especially internationally. If any lines of communication were working, they would be completely jammed.
Plot hole: After leaving the Santa Monica Airport the pilot decides for no apparent reason to fly into Downtown and fly between the buildings. Anyone from LA would know that in order to actually fly into downtown from the airport one would have to actually aim for it. It's not like you take off from the airport and then you are stuck having to fly in amongst tall skyscrapers.
Answer: Because it's the 21st December in the MAYAN calendar. In the calendar most people use, it was actually July.