If Mt of asteroid impact roughly equates to a nuclear weapon, then this is pretty bad for a metropolitan area but not enough to put a big dent in humanity.
There's a 3 in 4 chance an asteroid hitting the earth will hit water, and of the remaining change about 50/50 it hits a desert or ice sheet (Antarctica, Greenland).
Depending on the amount, if landing on solid earth, the effect of dust ejected into the atmosphere might be critically significant in terms of energy dynamics and solar energy production.
I think it if it's far enough out you only need to change it's trajectory only very slightly to reduce to the probably of impact to something much less
