But if the entire asteroid is to crash into the planet, the impact will be as hard as in the Tunguska blast, which in 1908 knocked down trees over a total area of 2,150 sq km (830 sq miles) in Siberia.
It could do a lot of damage if it landed in the right place, but it's a bit of a stretch to call it an existential risk.
I don't believe anyone was calling it an existential risk - rather using it as a reminder to people that such existential risks do exist and are not that far beyond what we see here. And, of course, that we can take active measures to oppose such risks and that we are not, in general, taking sufficient measures.
http://neo.jpl.nasa.gov/risk/2012da14.html
http://rt.com/news/paint-asteroid-earth-nasa-767/
Seems like a good opportunity to bring up existential risks. And A friendly reminder that NASA is in fact pretty damned important.
Thoughts?