They were talking about hiding in caves as if the dust to be caused by incoming comet was poisonous. Now, the resulting dust would block sunlight and kill plants and be lethal in that regard. But, I don't think the dust itself would be any worse than the dust in coal mines which caused black lung or the dust in textile mills which caused brown lung.
So, maybe the strategy is to put resources into dust masks and grow lights, and keep the power plants running.
And better yet might be multiple strategies to deflect the comet.
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I did like many scenes in the movie.
For example, President Tom Beck talking: We have a choice, right now. . . . I wish [pause] No, that's not the right word. That's not what I mean. What I mean is, I believe in God. I know many of you don't. . . .