re: the extinction of mankind
Cometary impact appears to be chaotically regular on a 26 million year basis. Where exactly we are in this cycle is currently unknown. NASA has not spent enough money.
Further, we have no idea whether the recent Earth impacts of fragments of Comet Encke are unusual or an indication of the current cometary flux. NASA has not spent enough money.
Not only that, we have no idea whether any of those fragments remain. NASA has not spent enough money.
As a possible indication of a current cometary flux higher than the average flux, we do have the example before us of Shoemaker-Levy 9 impacting Jupiter a few years back.
Now, exactly what kind of warning do you expect to be given?
ep