There are many theories out there about the destruction of the world. There is one claim that there will be nuclear war, but the more important claim is one used by Christians. Many Christians believe that one day the world may be hit by a large meteor because of certain verses in the book of Revelation that claim a large rock with destroy a third of men. Both events would lead to a 'nuclear winter.' A nuclear winter would be caused if something like smoke or dust blocked out the sun long enough for the whole earth to cool down, there would be no plant life and all of the earth would be sent into turmoil and death. But there is one problem, the Bible claims that as long as this planet exists there will always be summer and winter. Therefore there cannot be a world wide nuclear winter or anything close to it.

"While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease." (Genesis 8:22)

That's the Bible's opinion on the subject.