well if something like that happens we are all dead anyways, so i wonder why they even try to forcast it
not to mention they say there are astroids out there that would only give us about 2 years notice if they came into our path. That is not enough time to redirect the rock, by means of powerful lasers and redirected sunlight to slowly push the astroid off course.
Nuclear weapons are pretty much ruled ineffective due to the size of these deadly meteors, and even if we could blow them apart, all that mass is still headed towards us just in a few more peices.
the only chance the human race has at survival is expansion to other planets. If not in our society, maybe future ones thousands of years from now will be able to conquer the universe, cause after all we now know the earth is not the only habitable place, there are millions of destinations out there- the technolgy just has to catch up