Surface air temperature changes following a full-scale nuclear war averaged for June, July, and August of the year following the conflict. Effects are largest over land, but there is substantial cooling over oceans, too. The warming over Antarctica in year 0 is for a small area, is part of normal winter interannual variability, and is not significant.
Global temperatures 1 year after 150,000,000 tons of smoke enter stratosphere. Source: Alan Robock, Luke Oman, and Georgiy L. Stenchikov, Nuclear winter revisited with a modern climate model and current nuclear arsenals(2007). Journal of Geophysical Research.