Nuclear winter (also known as atomic winter) is a hypothesized global climatic effect most often considered a potential threat following a countervalue (or city-targeted), nuclear war, as a result 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 in the air for years, or even decades, and during this time it causes massive planet-wide temperature drops ("winters"). The climate models in the public domain suggest that the ignition of 100 firestorms, comparable in intensity to that observed in Hiroshima in 1945, would produce a "small" nuclear winter. The burning of these firestorms would result in the injection of soot (specifically black carbon) into the Earth's stratosphere, producing an anti-greenhouse effect that lowers the Earth's surface temperature. The models conclude that the cumulative products of 100 of these firestorms would unmistakably cool the global climate by approximately 1 °C (1.8 °F), largely eliminating the magnitude of anthropogenic global warming for two to three years. The authors speculate, but do not model, that this would have global agricultural losses as a consequence. A much larger number of firestorms, however, was the initial assumption of the computer modelers that coined the term in the 1980s. These were speculated to be a result of any large scale employment of countervalue city-airbursting nuclear weapon use during an American-Soviet total war. This larger number of firestorms, which are not, in of themselves modeled, are presented as causing nuclear winter conditions as a result of the smoke inputted into various climate models, with the depths of severe cooling lasting for as long as a decade, summer drops in average temperature by about 20 °C (36 °F) in core agricultural regions of the US, Europe, and China, and by as much as 35 °C (63 °F) in Russia. This cooling was produced due to a 99% reduction in the natural solar radiation reaching the surface of the planet in the first few years, gradually clearing over several decades. 1. \n* REDIRECT As nuclear devices need not be involved in the ignition of a firestorm, the term is a common misnomer. This is due to, in greatest part, the vast majority of published papers stating, without qualitative justification, that nuclear explosions are the cause of the modeled firestorm effects. The only phenomenon that is scrutinized and computer modeled in the nuclear winter papers is the climate forcing agent of firestorm-soot, a product which can be ignited and formed by a myriad of other, more common, means. On the fundamental level, it is known that firestorms can inject soot smoke/aerosols into the stratosphere, as each natural occurrence of a wildfire firestorm has been found to "surprisingly frequently" produce minor "nuclear winter" effects, with short-lived, almost immeasurable drops in surface temperatures, confined to the global hemisphere that they burned in. This is somewhat analogous to the frequent volcanic eruptions that inject sulfates into the stratosphere and thereby produce minor, even negligible, volcanic winter effects. A suite of satellite and aircraft-based firestorm-soot-monitoring instruments are at the forefront of attempts to accurately determine the lifespan, quantity, injection height, and optical properties of this smoke. Information regarding all of these properties is necessary to truly ascertain the length and depth of the cooling effect of firestorms, independent of the nuclear winter computer model projections. Presently, from satellite tracking data, stratospheric smoke aerosols are removed in a time span under approximately two months. The existence of any hint of a tipping point into a new stratospheric condition where the aerosols would not be removed within this time frame remains to be determined.

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