A purely pragmatic response (sneakily ducking your point):
A. Taken together, items 1 & 3 imply a lack of scientific consensus, hence
in the political world nothing probably could happen regardless of items 3
B. If there was a scientific consensus of sorts (recognizing that all
scientists will seldom agree on issues of substance), and if item 2 becomes
a salient point, then our pluralistic national mindset would force us to
cover our eyes and await our doom in order not to give preference to a
particular religious perspective.
A Christian response might depend upon one's eschatalogical viewpoint. If
such a catastrophe should actually be God's global method of ushering in
the new heaven and new earth, who are we to intervene? A sort of
Christianized dualism like the "think globally, act locally" ecomindset,
Lots of room for equivocation.
BTW, why not just name your scenario the threat of a major meteor impact
with the earth?