Nuclear Winter
Nuclear winter is a theory estimating the global climatic consequences of a nuclear war: prolonged and worldwide cooling and darkening caused by sunlight-blocking smoke and soot entering the atmosphere. During the Cold War after World War II, the concern about nuclear weapons was increasing all over the world. Initially, only the danger of radioactive fallout was recognized, but later also the possible environmental effects of a nuclear war became the subject of several studies. The term nuclear winter was first defined and used by American astronomer Carl Sagan (1934–1996) and his group of colleagues in their 1983 article (later referred to as the TTAPS-article, from the initials of the authors' family names). This article was the first one to take into consideration not only the direct damage, but also the indirect effects of a nuclear war.
The basic assumption during a nuclear war is that the exploding nuclear warheads would create huge fires, resulting in smoke and soot from burning cities and forests being emitted into the troposphere in vast amounts. This would block the sun's incoming radiation from reaching the surface of Earth, causing cooling of the surface temperatures. The smoke and soot soon would rise because of their high temperature, allowing them to drift at high altitudes for weeks without being washed out. Finally, the particles would settle in the Northern Hemisphere mid-latitudes as a black particle cloud belt, blocking sunshine for several weeks. The darkness and cold, combined with nuclear fallout radiation, would kill most of Earth's vegetation and animal life, which would lead to starvation and diseases for the human population surviving the nuclear war itself. At the same time, the upper troposphere temperatures would rise because the smoke would absorb sunlight and warm it up, creating a temperature inversion, which would keep smog at the lower levels. Another possible consequence is that nuclear explosions would produce nitrogen oxides, which would damage the protective ozone layer in the stratosphere, thus allowing more ultraviolet radiation to reach the earth's surface.
Although the basic findings of the original TTAPS-article have been confirmed by later reports, some later studies report a lesser degree of cooling would occur, only around 25 degrees of temperature drop and only for weeks instead of the initially estimated months. According to different scenarios, depending on the number of nuclear explosions, their spatial distribution, targets, and many other factors, this cloud of soot and dust could remain for many months, reducing sunlight almost entirely, and decrease average temperatures to as low as −40°C in the Northern Hemisphere continents. There are other studies, that mention the possibility of a not so severe nuclear winter as originally estimated, hence it is named a nuclear fall. Other researchers even talk about nuclear summer, stating that a worldwide warming would follow a nuclear war because of the many small contributions to the greenhouse effect from carbon dioxide, water vapor, ozone, and various aerosols entering the troposphere and stratosphere. What all scenarios agree on is that a nuclear war would have a significant effect on the atmosphere and climate of the earth and, consequently, many aspects of life such as food production or energy consumption would be drastically effected.
Opponents of the nuclear winter theory argue that there are many problems with the hypothesized scenarios either because of the model's incorrect assumptions (e.g., the results would be right only if exactly the assumed amount of dust would enter the atmosphere, or the model assumes uniformly distributed, constantly injected particles), or because important effects, processes and/or feedback mechanisms are not taken into consideration (e.g., the moderating effects of the oceans, or small-scale processes are not included, or the biological effects are not addressed), or simply because there are many uncertainties involved in the estimates. The topic even at present day remains controversial, because the exact level of damage, along with the extent and duration of the effects, cannot be agreed upon with full confidence.
Atmospheric Circulation; Atmospheric Composition and Structure; Atmospheric Inversion Layers; Atmospheric Lapse Rate; Atmospheric Pollution
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