Oddly, there is excellent evidence that giant meteors and comments have struck the Earth in the past, and we have actually observed them striking other planets.The risk is infinite, with the possibility of total destruction of civilization quite high in such an event. We have, or could quickly develop, the technology to detect and deflect these threats, at much less cost than anything that would be effective against global warming. Yet we do nothing.
Someone please point out to me why a genuine, if statistically small, risk should receive no attention as compared to a purely theoretical risk.
If you were to do some actual calculations of the type of detection and analysis capability, and the power required to effect a lessening of a comet or meteor event, and then the cost-effectiveness to construct and maintain a "planetary defense" against such a rare event, you might not make such a sweeping comment. This problem is not trivial, and the cost of acquiring and maintaining such a system right now is simply out of reach. I wish that were not the case, but that is the truth.
The energy of a such a mass rushing toward Earth in some such event is equivalent to billions or even trillions of H-bombs. It might well require the power of thousands of such engines to sufficiently deflect such a moving body. NASA gets flak for contemplating the launch of extremely small reactors for powering experiments, yet you wish to propose launching the equivalent of hundreds or many thousands of H-Bombs with some of the most powerful and untested rocketry, and maintaining that in pristine condition for hundreds of years or even millenia?!
God/Nature is much more powerful than most humans imagine.
Even a simple thunderstorm moves millions of tons of mass... we, though we are so proud of our "high-technology", are not even in the same league.
Because building rockets creates high paying jobs for mostly smart male American engineers, intensifying world-wide envy. That will never do. Global warming on the other hand appears to be useful to the envious to destroy American prosperity. Unfortunately for them the rocket engineers instead will be hard at work developing climate management technologies such as cloud, snow, and saltwater algae making.