Well written and informative article @dommaraju .
One other thing worth mentioning though is that the global threat of a Nuclear War actually has very little to do with the energy of the blast, nor the radiation left behind. From a global perspective, and looking at the possible trheat of extinction, the main threat is the burning cities and the resulting "Nuclear Winter" caused by the smoke released into the atmosphere. I think it would only take the destruction of about 100 medium-sized cities to cause a decade+ long winter, which would be enough to mess up the seasonal cycles and air quality to the point where Human life could not exist without the aid of tehcnology.
It's quite interesting how we came to understand this by studying dust storms on the planet Mars. :)