Nuclear winter is a hypothetical cold spell that could happen to a planet after a nuclear war on a larger scale. Catastrophic effects of climate change are particles in the atmosphere prevents the sun's rays from reaching the surface. Temperature reductions to several tens of degrees to occur with subsequent mass extinction of plants and animals of extreme cold weather.
Dr. Lisa Park thought that planet Novus had suffered a nuclear winter after hearing the two nations on Novus were in the cold war with each other. Lt. Matthew Scott's shuttle analyzed the surface. He determined that the surface of Novus had colder temperatures but there was no nuclear winter just volcanic winter. (SGU: "Epilogue")