The movie shows people freezing to death because of a super-storm bringing freezing air from the "upper troposphere." Could that really happen?
NASA: No. Firstly the upper troposphere is not as cold as portrayed (minima near -80 C (-110 F) at about 15 to 20 km), and this cooling is mainly due to the pressure decreasing with height. As air rises it cools due to this effect alone, similarly as it is brought down, it warms up by 6-10 degrees per kilometer.
NSIDC: No, this part of the movie is somewhat far fetched. On the same general subject, changes are expected in atmospheric temperature as well as on the surface. Shown below is a summary. Because GHGs absorb heat in the atmosphere, they change the temperature within its various layers. Finding the pattern illustrated in the diagram of warming and cooling (diagrammed below) would be definitive proof that CO2 and CH4 were the cause of surface warming. But this is not as easy as it may sound; there are not many weather stations in the upper troposphere (aircraft do not do the job well because they affect the air around them). Balloon and satellite data do appear to show the expected trends. The topic is the subject of active scientific debate.