What would happen if an asteroid the size of Mt. Everest hits earth?

Question: What would happen if an asteroid the size of Mt. Everest hits earth?
- Keywords:
  end of the world,
  natural disaster,
  space
Asked by smiddleton to Alan on 10 Mar 2014.
- Alan Fitzsimmons answered on 10 Mar 2014:
  
  It would be a bad day. The fireball from the resulting explosion would destroy a small country. There would be tidal waves and earthquakes all over our planet. And there would be so much pulverised rock thrown up into the atmosphere it would stay there for years, dimming the sun. This would lower temperatures so much it would stop crops growing, leading to famine throughout the world.
  
  Something like this happened 65 million years ago, when a slightly bigger asteroid hit the Earth and helped kill off the dinosaurs and many other types of animal. It left a crater over 100 miles across, which is now buried under the sea near Mexico.
  
  Luckily, asteroids this big are easy to spot with todays telescopes. We have found and tracked them all, and none will be coming near us in the next few hundred years.

Question: What would happen if an asteroid the size of Mt. Everest hits earth?