What I am more concerned about is the Asteroids that could level a city and cause tens-of-thousands of deaths. These can happen with more regularity that we would think. However it is fully within or power to be able to deflect or destory a asteroid of this size. The Karakul impact in Tajikstan was around 5 million years ago and left a 52km diameter crater. Could you imagine something like this impacting in populated area?