I would say that is very hopeful thinking. The biggest threat does not actually come from the explosion itself (okay, yes, the explosion is also bad), but from the nuclear fallout that occurs after.
Nuclear fallout can affect HUGE areas of the world. When a nuclear device is detonated, radioactive particles get launched into the atmosphere that can travel across the globe.
I also see comments below about the bombs dropped on Japan - people need to keep in mind that was 65 years ago AND the bomb types were nuclear FISSION, not nuclear fusion. There's a distinct difference. I'm not exactly sure what types of bombs Pakistan and India have, but it's probably bad either way.