Answer:
Nuclear Winter is a term that describes the after effects of a nuclear war. It is similar to a supervolcanic eruption in that the bomb will eject huge amounts of ash into the earth's stratosphere(were there clouds are and the planes fly) which would absorb the sunlight and get heated up, lifting it higher where it would persist for years. As sunlight would not be able to penetrate through, tempreatures on the surface would drop drastically.