Scientists claim that the Tanguska explosion was a comet hitting the earth. Many claim it was actually a UFO since they say the craft made a turn before exploding. But if it actually was a comet, we know the destructive power of comets. The next time around, a comet could wipe out life on earth, if it's large enough.
Comets are often faster than meteors, so the explosion after impact would be greater. If one can be detected and determined to have earth as the target, there are various things that could be done to either moderate the destructiveness or prevent the comet from hitting this planet. Using nuclear warheads to destroy the comet is an option. If enough brute force is used, a comet the size of Central Park might be reduced to rubble that will burn up harmlessly in the atmosphere.
If it is determined that a comet will hit earth within a year, a robotic rocket could be sent to it to latch onto it and push it out of a trajectory with earth. That's why in the future there will be stations in the Kuiper Belt to keep an eye on objects that will be heading toward the inner planets of the solar system. A little nudge in the Belt will mean a huge push won't be needed later.
Particle beam weapons will be able to carve up a comet into manageable chunks if given enough time. By using particle beams and nuclear explosives, a comet the size of Central Park could be reduced to harmless rubble within a few days. If President Nixon had taken the advice of a person from Indiana in 1970 to build a satellite defense system which relied on charged particle beams that were nuclear powered to destroy incoming missiles and warheads, maybe such a system could have been in place well over a decade ago. Since the weapons could be turned to hit targets out in space, a comet out as far as Mars could be hit by the beams and chipped away at long enough that by the time it reached earth, it might be a shower of debris with chunks no larger than refrigerators. They would be dangerous. But they wouldn't be large enough when they struck earth to destroy it.
Further in the future, once we start building repulsion-drive engines, we could send "space tugs" to a comet that is as little as three hours from hitting earth and push it away from hitting the planet and send it to the sun. If the energy mass expelled by the engines is 10% of the mass of the comet, it should be redirected enough to avoid earth. Just as long as it doesn't hit the moon which could send it toward the earth which would be the end of all life on this planet, a comet the size of Manhattan Island could be safely turned from earth and sent toward the sun.
By the next century, if we can't prevent the destruction of this planet by comets, it will mean we haven't progressed enough technically. That should not be the case because the survival of life on earth depends on our ability to prevent such a disaster.