There have been 26 asteroid impacts recorded from 2000 to 20013 by the Nuclear Test Ban Treaty Organisation's infrasound detection network. Our friend Félix Pharand-Deschênes sent us this graphic showing the atmospheric impact points. It demonstrates that they're more common, and dangerous, than we would like to believe.
All these asteroids exploded too high in the atmosphere to cause major damage on the surface. The meteor in Chelyabinsk Oblast, Russia, was the only one big and close enough to a population centre to cause material damages and injuries. In this case the atmosphere absorbed about 500 kilotonnes (or 1.8 petajoules). For comparison, Little Boy unleashed 15 kilotonnes over Hiroshima.
The worse thing, however, is that these impacts weren't predicted. They caught us by surprise. Had they entered at the right angle, they could have taken out a city like New York.
According to the B612 Foundation—an organisation working to protect Earth from asteroid strikes—the 26 explosions ranged from 1 to 600 kilotonnes. This video explains it all: