Factual error: Several scenes in the movie show the tidal waves and tsunamis sweeping people and objects away, which is utter fantasy. The air pressure wave that is in front of the tidal waves and tsunamis would blow people and objects away long before the water did.
Factual error: After taking off from Las Vegas for Tibet, our heroes try to refuel the Antonov in Hawaii, only to find the islands devastated. The route from Las Vegas to Tibet takes you nowhere near Hawaii. In fact, Hawaii is only 500 km (300 miles) closer to Tibet than Las Vegas. Also, they expect to go down somewhere in the South China Sea, but the route from Hawaii to Tibet would take them just north of Japan and nowhere near the South China Sea, which is 3000 km (1900 miles) further south.
Factual error: When Adrian is looking at Jackson's license, it shows his first name, last name. As in: JACKSON, CURTIS. Should be last name first, first name last. As in: CURTIS, JACKSON.
Factual error: In the beginning of the film, when they are in India, the scientist says the temperature could reach 100 degrees Fahrenheit. India uses the metric system, not imperial.
Answer: Because it's the 21st December in the MAYAN calendar. In the calendar most people use, it was actually July.