The sudden release of Energy isn't what would cause extinction from nuclear weapons, it's the persistent fallout which would make the entire surface of the plan

The sudden release of Energy isn't what would cause extinction from nuclear weapons, it's the persistent fallout which would make the entire surface of the planet uninhabitable for many years. http://en.wikipedia.org/wiki/Nuclear_winter http://en.wikipedia.org/wiki/Nuclear_winter "Based on new work published in 2007 and 2008 by some of the authors of the original studies, several new hypotheses have been put forth.[16][17] A minor nuclear war with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas could produce climate change unprecedented in recorded human history. A nuclear war between the United States and Russia today could produce nuclear winter, with temperatures plunging below freezing in the summer in major agricultural regions, threatening the food supply for most of the planet. The climatic effects of the smoke from burning cities and industrial areas would last for several years, much longer than previously thought. New climate model simulations, which are said to have the capability of including the entire atmosphere and oceans, show that the smoke would be lofted by solar heating to the upper stratosphere, where it would remain for years. Compared to climate change for the past millennium, even the smallest exchange modeled would plunge the planet into temperatures colder than the Little Ice Age (the period of history between approximately A.D. 1600 and A.D. 1850). This would take effect instantly, and agriculture would be severely threatened. Larger amounts of smoke would produce larger climate changes, and for the 150 teragrams (Tg) case produce a true nuclear winter (1 Tg is 1012 grams), making agriculture impossible for years. In both cases, new climate model simulations show that the effects would last for more than a decade."