There are a whole range of options, if we have enough warning and invest in the technology[1]. My personal favourite is the gravity tractor:

> One more alternative to explosive deflection is to move the asteroid slowly over a time. Tiny constant thrust accumulates to deviate an object sufficiently from its predicted course. Edward T. Lu and Stanley G. Love have proposed using a large heavy unmanned spacecraft hovering over an asteroid to gravitationally pull the latter into a non-threatening orbit.

And the same technology could be used to actively "capture" asteroids for fun and profit

[1] https://en.wikipedia.org/wiki/Asteroid_impact_avoidance

An asteroid that size has a very small escape velocity, on the order of a few meters per second. I think a mass driver which broke off small chunks of asteroid and hurled them to escape would not take too much power and be able to disassemble the asteroid in less than one orbit. (Advanced detection would be a plus here.) If we aimed the ejecta, to get a momentum change in a given direction, we would not have to completely disassemble the asteroid, because its orbit would change and eventually miss Earth. Complete disassembly would be safer, because small chunks would burn up in Earth's atmosphere.

Thank god that Hollywood had the foresight to give us a playbook (and live action simulation) for this exact situation: http://www.imdb.com/title/tt0120591/

And http://www.imdb.com/title/tt1307068/ Seeking a Friend for the End of the World

And Deep Impact http://www.imdb.com/title/tt0120647/

ICBMs reach a velocity of about 5 km/sec., aren't reprogrammable in minutes to shoot at spsce rocks, and US ones at least carry weapons of less than 500 kt. This isn't going to do it. If we want to use nukes, which is questionable, the devices need to already be in high orbit to respond fast enough, have a radar guidance system, and be much more powerful. This is also a recipe to trigger WW 3.

I'm not suggesting it as a "minutes to go" safety measure. More of a "we have tons of rockets with nukes on them that can make it into space" just sitting around measure.

Making it to space isn't enough. They have to be able to escape completely and deliver a very large warhead to the asteroid.