I haven't seen this movie yet, perhaps because I didn't understand how global warming is supposed to lead to a new ice age. I am aware that it might become a bit colder in Europe because the Gulf stream might change its path, but icy cold? Makes no sense to me.
Well, the difference between subtlety and gross exaggeration. I rather take Scotty's "captain, there be whales here" over "the world will end and you are all gonna die".