Well as I recall, the premise of “Day After Tomorrow” was that global warming shut down the Gulf Stream, which stopped the warm water from the equator from heading north, which caused an ice age in the northern hemisphere.
So in the movie, the freeze was caused by global warming.
The movie sucked, but the special effects were cool, especially the money shot of the tidal wave taking out NYC.
The movie indeed sucked, a lot of that had to do with the over-the-top political messages. For instance, the USA is messed up and Mexico lets in a flood of Americans across the southern border and cares for them. I don't believe that! Mexicans would have a field day shooting Americans fleeing south, and steal their possessions. They are not us.