Researchers from the University of Southampton (UK) have just released a report on a modeling program they created which details the likelihood and consequences of a small asteroid (< 1km) hitting Earth. According to Science Daily, a collision with a small asteroid would be devastating:
Initial investigations have examined how the consequences of an impact change with increasing impact energy. Taking a spherical stony asteroid travelling at 12,000 miles per second and varying the diameter to increase kinetic energy, the results indicate that a 100 metre diameter asteroid will predominantly cause localised casualties and damage across a few countries when impacting on either land or ocean. However, the consequences of a 200 metre diameter asteroid hitting the ocean increase significantly, with the generated tsunamis reaching a global scale. At 500 metres in diameter, almost any ocean impact will generate significant casualties and economic cost across the world.
Interestingly, the report specifies which countries are most at risk for a direct impact. Those countries are China, Indonesia, India, Japan, the United States, the Philippines, Italy, the United Kingdom, Brazil and Nigeria. I'm pretty surprised not to see Russia on there...it's huge!
To see what a BIG asteroid would do to Earth, watch this ridiculous video: