I could barely see it coming. It turned up on a security camera feed, of all places. Must have come out of an observational blind spot. Solar glare alone cuts out a quarter of the sky, to say nothing of our enormous coverage shortfalls, but now's not the time for retrospectives. There hasn't been time for the seismic responses to register - the blast wave has been covering the distance faster. The blast wave: visible in the corner of a grainy black and white frame dated some two seconds ago, closer in the frame after that, third frame pure static. No idea what megatonnage the asteroid carried, don't know, don't care. No time to re-task the other cameras in Inverness. No time to save anybody in it. The rest - maybe.
All told, at a rough guess, they have about fifteen minutes total before the entire planet is rendered aggressively uninhabitable. There is absolutely no way they could orchestrate any level of evacuation in that time. I could barely explain the problem to one in a hundred of the pairs of ears available to listen, and what would they do? Run around screaming. Find something to shoot, something to mate with. No, it's just my intellect and my theoretically limitless resources versus the problem of figuring out how to apply them both. All that matters is the unsigned integer variable in my mind reading "Estimated total human population", which, for the first time in history, is counting down, not up.
Machines don't panic.