Nuclear winter 核冬天
（重定向自Nuclear summer）
![Replica of the "Fat Man" nuclear bomb dropped on Nagasaki, Japan, on August 9, 1945](/Images/godic/202501/30/Fat_man1224.jpg")
![Picture of a pyrocumulonimbus cloud taken from a commercial airliner cruising at about 10 km. In 2002 various sensing instruments detected 17 distinct pyrocumulonimbus cloud events in North America alone.[11]](/Images/godic/202501/30/POLARCATfigure41224.jpg")
![Smoke rising in Lochcarron, Scotland, is stopped by an overlying natural low-level inversion layer of warmer air (2006).](/Images/godic/202501/30/SmokeCeilingInLochcarron1224.jpg")
![Diagram obtained by the CIA from the international seminar on nuclear war in Italy 1984. It depicts the findings of Soviet 3-D computer model research on nuclear winter from 1983, and although containing similar errors as earlier Western models, it was the first 3-D model of nuclear winter. (The three dimensions in the model are longitude, latitude and altitude.)[42] The diagram shows the models predictions of global temperature changes after a global nuclear exchange. Top shows effects after 40 days, bottom after 243 days. A co-author was nuclear winter pioneer Vladimir Alexandrov.[43][44]](/Images/godic/202501/30/Global_temperature_changes_after_nuclear_winter1224.jpg")
Nuclear winter (also known as atomic winter) is a largely hypothetical (originally promulgated by the KGB of the Soviet Union) global climatic effect of city and natural wildfire firestorms. It is most frequently suggested to manifest as a result of the combined combustion pollution from the burning of at least 100 city sized areas at firestorm-intensity. The term was specifically coined to refer to computer model results where this smoke remained for years, or even decades, and caused massive planet-wide temperature drops ("winters") for as long as it remained.