text: Possibly, if they're in the 500k yield range, that would be 15,000 kilotons detonating or 15 million tons of TNT.   Would that be enough to trigger a nuclear winter?  ....depends.\n\nA Nuclear Winter threshold level of nuclear use is around 100 - 500 warheads, particularly if they are targetted at high carbon targets such as oil installations or coal storage areas.  Prolonged period of cold and dark after nuclear war due to large amounts of carbon particulate aerosols being injected high into the atmosphere would kill most of the earth, i suspect there will be some survivors. ...those in deep shelters with 1-2 yrs of provision or isolated settlements that are self-sustaining.\n\nConsider Tasmania. As an island in the southern hemisphere, nuclear winter effects would be minimised. It has large hydropower capacity for providing heat and power, and the large sheep population could help tide the modest human population through a failed harvest.