But there was a 15 megaton event over Siberia in 1908 that would have flattened the whole of London if the circumstances had been only slightly different. And Chinese records tell us of a meteorite explosion killing tens of thousands in the 15th century. Statistics can be misleading. Take air crashes. I'm a member of the Qantas frequent flyer club, an airline that has never had an accident.
Circumstances can change quickly.
Until recently Concorde was regarded as a paragon of air safety. Two decades ago virtually everyone, weather forecasters included, thought that hurricanes never hit England. The only nation spending any sensible amount on asteroid defence is the United States. In effect we too, need to declare war on the heavens. Duncan Steel is reader in space technology at the University of Salford.