Pardon the glibness but I feel humanity will survive longer without an asteroid-deflecting technology than if we own 1Gt nuclear devices.
If that's the scale required, I propose ignoring the possibility.
If that's the scale required, I propose ignoring the possibility.
The most dangerous nukes are actually the smallest, since politicians may convince themselves that just a few small nukes is permissible, resulting in a rapid escalation that sees every major city showered with megaton h-bombs, destroying civilization and sending humanity into a poisoned dark age.
If it seems implausible that politicians might use tactical nukes, ask what those nukes were created for. The US made many thousands of them to be used against a conventional Soviet ground invasion of West Germany; lobbing small nukes at tank columns. Escalation from a conventional war to a nuclear war was a common assumption in the military planning of the late cold war. But sides anticipated it and were prepared to perform that escalation themselves.
In fact I believe that anything over the low tens of Mt is considered impractical for military use.
Agreed, a big device doesn't really alter the balance of power, which is why both the Americans and Soviets abandoned the path of bigger and bigger devices by 1962, leaving lots of engineering possibilities on the table to instead focus on miniaturization.
It's not easy, but it's something like a 3-4 order of magnitude multiplier if you figure out how to do it.