So, as part of a fictional setting, I sent asteroid 1999 FN53 (which is 900 metres in diameter) on a collision course with Earth as part of a terrorist attack, at a speed of 150 km/s, at an angle of 57 degrees. It crashes 2 km west off the coast of Guam. If 3.04 teratonnes worth of TNT are released and Earth has 13 billion humans by the time this happens, is it extinction-level?
EDIT: Actually, regarding the situation on population sustainability, I went with the recent version of the UN medium estimate of 11.2 billion by 2100 and assumed a growth rate of 0.04% over 300 years. So....there. :/ Also, that asteroid was accerated to that speed at the approach upon Earth, and the initial acceleration aftr it was moved was 30 km/s, with its pre-change speed being 14 km/s. So, there. A few gpod explanations, and the method was to construct 5 large mass drivers and use the asteroid itself as propellant.:/