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Nuclear Winter

Nuclear Winter. Although there had been earlier antecedents, the widespread public debate about nuclear winter began in 1982 with the suggestion by Paul Crutzen, at the University of Colorado, and John Birks, at the Max Planck Institute, that a large‐scale nuclear war could produce such conflagrations of forests that a smoke pall covering perhaps half the northern hemisphere would develop. This would absorb enough of the light from the Sun that there could be serious and prolonged reductions in photosynthesis and in temperatures over that part of the planet, resulting in catastrophic agricultural failure. The work was quickly picked up by R. P. Turco, O. B. Toon, T. P. Ackerman, J. B. Pollack, and Carl Sagan, who, on the basis of quantitative modeling, concluded that a large‐scale nuclear war could be expected, mainly as a result of the burning of cities rather than forests, to cause temperatures to drop by 36° C. (65° F.) and to remain below freezing for several months. Their work, commonly referred to as the TTAPS study, provided the basis for a number of other publications that appeared in the next three years bearing Sagan's name and the appellation “nuclear winter,” which he and Turco coined to describe the phenomenon.

Not surprisingly, these publications caused a considerable stir, given their wide circulation and some of the apocalyptic visions presented: that a major nuclear exchange would produce “the greatest biological and physical disruption of the planet in its last 65 million years” (a period that included the four great ice ages) and that the number of survivors would be reduced to prehistoric levels (presumably a fraction of 1% of those now alive). All of this was buttressed by claims that the TTAPS results were insensitive to wide variations in assumptions about parameters used in modeling. In fact, the results were anything but robust, as subsequent studies would make clear.

There were basically two kinds of problems. First, TTAPS was based on the simplifying assumption that the burning of cities would produce an instantaneous homogeneous distribution of smoke over the entire northern hemisphere, when in reality it would take some days for such spreading to occur, during which time much of the smoke would likely be removed by natural processes. Moreover, the modeling took no account of the warming effects of the infusion of relatively warm air from oceanic and tropical areas to continental interiors. More refined later modeling that did take account of these phenomena, and used comparable assumptions about amounts and characteristics of the smoke from fires, led to radically smaller temperature effects.

Second, there were a number of uncertainties in key areas which, if resolved, could plausibly lead at one extreme to no significant climatic effects, or at the other, to effects as dire as those discussed in 1983, a range of outcomes largely conceded by Turco and Sagan in a characterization of five different classes of nuclear winter by 1989.

The nuclear winter controversy was perhaps as much about policy as about geophysics. Advocates of enlarged programs for deterrence of nuclear attacks and for defense against them seized on the possibility of nuclear winter to buttress their case for such programs. In contrast, the most vocal proponents of the nuclear winter theory generally argued that it strengthened the case for reducing nuclear stockpiles and foregoing the development and acquisition of new nuclear weapons; and some argued that even if there were doubts about the phenomenon, it would be wise to base policy on “worst‐case analysis.” Others argued that war involving enough nuclear explosions to trigger nuclear winter would likely have consequences so catastrophic, at least for the nuclear weapons states, as to overshadow the possibility of nuclear winter in concerns about policy. (And some of those skeptical about the more dire prognostications warned particularly against worst‐case analysis being used as a basis for mitigative actions by countries not likely to be directly attacked, noting that such actions could well involve the use of scarce resources sorely needed for other purposes.)

By the early 1990s, nuclear winter was no longer a salient issue in geophysics or from a policy perspective, very likely because the geophysical case for it seemed so questionable; because the initiation of massive oil fires in Kuwait during the Persian Gulf War did not lead to significant climatic effects, as some had predicted; and probably most important, because concern about large‐scale nuclear attacks had largely dissipated with the end of the Cold War.
[See also War Plans.]

Bibliography

Paul J. Crutzen and and John W. Birks , The Atmosphere After a Nuclear War: Twilight at Noon, Ambio, Vol. II, no. 2–3 (1982), p. 114.
Paul R. Ehrlich,, Carl Sagan,, Donald Kennedy,, and and Walter Orr Roberts , The Cold and the Dark: The World After Nuclear War, 1984.
National Academy of Sciences , The Effects on the Atmosphere of a Major Nuclear Exchange, 1985.
Nuclear Winter, Vol. 1, no. 2 (1985), p. 112.
A. Barrie Pittock, et al. , The Environmental Consequences of Nuclear War, Vol. I; and Mark A. Harwell and Thomas Hutchinson, Vol. II, 1985.
Stanley L. Thompson and and Stephen H. Schneider , Nuclear Winter Reappraised, Foreign Affairs, Vol. 64, no. 5 (Summer 1986), p. 981.

George W. Rathjens

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Nuclear Winter

Nuclear Winter

AGNES GALAMBOSI

Nuclear winter is a meteorological theory estimating the global climatic consequences of a nuclear waror a natural disaster such as a major asteroid impactthat injects large amounts or dust or water vapor into the atmosphere. Nuclear winter models predict prolonged and worldwide cooling and darkening caused by the blockage of sunlight.

During the Cold War, concern about the use of nuclear weapons initially concentrated on initial blast damage and the dangers of radioactive fallout. Subsequently, researchers began to explore the possible environmental effects of nuclear war. The term nuclear winter was first defined and used by American astronomer Carl Sagan (19341996) 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.

During a nuclear war, 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. According to nuclear winter theory, 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 to high altitude because of their high temperature and drift there 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 ensuing 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, because the smoke would absorb sunlight, the upper troposphere temperatures would rise and create a temperature inversion causing further retention of smog at the lower levels. Another predicted consequence is that nuclear explosions would produce nitrogen oxides that would damage the protective ozone layer in the stratosphere and allow more ultraviolet radiation to reach Earth's surface.

Although the basic findings of the original TTAPS-article have been confirmed by later reports and sophisticated computer modeling, some later studies report a lesser degree of cooling that would last for weeks instead of the initially estimated months. In the extreme, however, depending on the number of nuclear explosions, their spatial distribution, targets, and many other factors, a cloud of soot and dust could remain for many months, reducing sunlight almost entirely and decreasing average temperatures to well below freezing over a majority of the densely inhabited areas of the Northern Hemisphere.

The nuclear winter scenario remains scientifically controversial because the exact level of atmospheric damage, along with the extent and duration of subsequent processes cannot be agreed upon with full confidence. 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 because the model assumes uniformly distributed, constantly injected particles). Other critics of the nuclear winter scenario point out that the models used often do not include processes and/or feedback mechanisms that may moderate or mitigate the initial effects of nuclear blasts on the atmosphere (e.g., the moderating effects of the oceans). In contrast to nuclear winter models, some climate models actually postulate a "nuclear summer," resulting from a worldwide warming caused by many small contributions to the greenhouse effect from carbon dioxide, water vapor, ozone, and various aerosols entering the troposphere and stratosphere.

What all scenarios and models forecast, however, is that a nuclear war would have a significant effect on the atmosphere and climate of Earth. This in turn would drastically and negatively affect many aspects of life such as food production and energy consumption.

FURTHER READING:

BOOKS:

International Seminar on Nuclear War and Planetary Emergencies, 20th Session: The Role of Science in the Third Millennium, Man-Made & Natural Disasters, Post-Berlin-Wall Problems-Nuclear Proliferation in the Multipolar World. Singapore: World Scientific Publishing, 1997.

Weinberger, Casper. "The Potential Effects of Nuclear War on the Climate." Nuclear Winter, Joint Hearing before the Committee on Science and Technology and the Committee on Interior and Insular Affairs, U.S. House of Representatives. Washington, D.C.: Government Printing Office, 1985.

PERIODICALS:

Ehrlich, Paul, et al., "Long-Term Biological Consequences of Nuclear War." Science 222, 4630 (1983).

Turco, R. P., O. B. Toon, T. P. Ackerman, J. B. Pollack, and Carl Sagan. "Nuclear Winter: Global Consequences of Multiple Nuclear Explosions." Science 222, 4630 (1983).

White Paper. "Nuclear Winter: Scientists in the Political Arena." Physics in Perspective 3:1 (2001):76105.

SEE ALSO

Nuclear Detection Devices
Nuclear Emergency Support Team, United States
Radiation, Biological Damage
Radiological Emergency Response Plan, United States Federal

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Nuclear Winter

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 (19341996) 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.

See also Atmospheric circulation; Atmospheric composition and structure; Atmospheric inversion layers; Atmospheric lapse rate; Atmospheric pollution

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nuclear winter

nuclear winter, theory holding that the smoke and dust produced by a large nuclear war would result in a prolonged period of cold on the earth. The earliest version of the theory, which was put forward in the early 1980s in the so-called TTAPS report (named for last initials of its authors, Richard P. Turco, Owen B. Toon, Thomas P. Ackerman, James B. Pollack, and Carl Sagan), held that the ensuing low temperatures and prolonged periods of darkness would obliterate plant life and seriously threaten the existence of the human species. Later models, which took into account additional variables, confirmed the basic conclusions of the TTAPS report and suggested that the detonation of 100 megatons (the explosive power of 100 million tons of TNT) over 100 cities could produce temperature drops ranging from 5 to 15 degrees.

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Nuclear Winter

Nuclear winter


Nuclear winter is a term given to what would happen to Earth's environment following a large-scale nuclear war. In effect, the entire planet would be plunged into a very bitter winter that would last months or years. The most severe consequence would be that Earth's climate would become too cold to grow vital food crops, including rice, wheat, and corn. It would likely lead to the starvation of hundreds of millions of people who survived the initial nuclear blasts. In effect, it would likely be the end of civilization.

However, with the end of the Cold War and the breakup of the Soviet Union, the threat of a full-scale nuclear exchange between the United States and Russia has greatly diminished. Today, the term nuclear winter is also used to describe the aftermath of any event that sends huge amounts of particulate matter into the atmosphere , blocking the sun and drastically cooling Earth's atmosphere. Such events could include the simultaneous eruption of a number of large volcanoes, or the impact upon the planet of a large comet or asteroid.

Although eight countries are known to possess nuclear weapons as of 2002, it was the thousands of warheads held by the United States and Russia that most worried scientists during the Cold War. A nuclear exchange between other countries, such as India and Pakistan, would not create a nuclear winter because most of the world's croplands would be spared.

Many of the horrible consequences of a global nuclear conflict have been well known for nearly half a century. Though much research has been conducted in this area, there is still much to be learned. Many scientists believe that the smoke produced as a result of a nuclear conflict would reduce the transmission of sunlight to Earth's surface over a significant portion of the planet. According to the theory, this reduction in sunlight would then cause a cooling on land surfaces of anywhere from 1865°F (1035°C). Interior parts of a continent would experience greater cooling than would coastal regions. Some parts of the planet that now experience a temperate climate might be plunged into winter-like conditions.

The idea of nuclear winter has been controversial ever since it was first proposed in 1983 by famed astronomer Carl Sagan (19341996). The U.S. National Academy of Sciences , the U.S. Office of Science and Technology Policy, the World Meteorological Organization, the International Council of Scientific Unions, and the Scientific Committee on Problems of the Environment , as well as dozens of individual scientists, have analyzed the potential for a nuclear winter and the problems that it might engender. These studies have not resolved the many issues surrounding a possible nuclear winter effect, but they have clarified a number of factors involved in that effect.

First, the fundamental logic behind a possible nuclear winter effect has been considerably strengthened. Experts estimate that about 9,000 teragrams (9 trillion grams) of finished lumber exist in the world. A large portion of that is found in urban areas that are likely to be the focus of a nuclear attack. By one estimate, anywhere from 2575% of the wood in an urban area would be ignited in a nuclear attack. A second resource vulnerable to nuclear attack is the world's petroleum reserves. Most experts agree that oil refineries, oil storage centers, and other concentrations of oil deposits would be likely targets in a nuclear attack. These materials would also serve as fuel in a widespread fire storm.

The main product of concern in the combustion of wood, petroleum, and other materials (plastics , tar, asphalt, vegetation, etc.) would be sooty smoke. This smoke would decrease solar radiation by as much as 50%. In addition, it would not easily be washed out of the atmosphere by rain, snow, and other forms of precipitation. Computer models have also shown that soot in the atmosphere may be more stable than first imagined. Studies also suggest that a nuclear winter effect could produce serious consequences for the ozone layer. One effect would be the dislocation of the ozone layer over the Northern Hemisphere towards the Southern Hemisphere. Another effect would involve actual destruction of the ozone layer by nitrogen oxide molecules carried aloft by smoke.

Scientists have studied a number of natural phenomena with nuclear winter-like effects. Volcanic eruptions, massive forest fires, natural dust clouds, urban fires, and extensive wild fires all produce massive amounts of smoke similar to what would be expected in a nuclear conflict. For example, massive wildfires in China during May of 1987 were found to reduce daytime temperatures in Alaska by 412°F (26°C) in ensuing months. Possible climatic effects from the enormous oil well fires during the Persian Gulf War , as well as recent volcanic eruptions, are also being studied. One scientist studying this phenomenon has said, however, that "severe environmental anomaliespossible leading to more human casualties globally than the direct effects of nuclear warwould be not just a remote possibility, but a likely outcome."

A number of scientists have challenged Sagan's findings, saying he overestimated the devastation that would result from a large-scale nuclear war. Several scientists suggested the result of such a war would be a "nuclear fall" rather than nuclear winter. While this would also be a disaster, the scientists suggested that it would not mean the end of civilization as Sagan predicted. The scientists explained that this is because Sagan greatly overestimated both the amount of smoke and dust that would be created and its duration in the atmosphere.

[Ken R. Wells ]


RESOURCES

BOOKS

Sagan, Carl, and Richard Turco. A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race. New York: Random House, 1990.

PERIODICALS

Marshall, Eliot. "Nuclear Winter Debate Heats Up." Science (January 16, 1987): 271274.

Overbye, D. "Prophet of the Cold and Dark." Discover (January 1985): 2432.

Seitz, Russell. "An Incomplete Obituary." Forbes (February 10, 1997): 123124.

Sinberg, Stan. "Springtime for Nuclear Winter." Omni (April 1992): 9899.

Turco, R. P., et al. "Climate and Smoke: An Appraisal of Nuclear Winter." Science (January 12, 1990): 166167.

ORGANIZATIONS

Manchester University Computing Society, Oxford Road, Room G33, Manchester, Great Britain M13 9PL 44(0)161-275-7329, Email: [email protected] compsoc.man.ac.uk, <http://www.compsoc.man.ac.uk/~samp/nuclearage/effect.html>

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Nuclear Winter

Nuclear Winter

Resources

Nuclear winter is a global climate event predicted in the 1980s by some scientists: after a nuclear war (the theory goes), prolonged, worldwide cooling and darkening would be caused by sunlightblocking smoke and soot entering the atmosphere. The term nuclear winter was coined by American astronomer Carl Sagan (19341996) and his colleagues in their 1983 article (later referred to as the TTAPS study, from the authors initials). This article was the first one to take into consideration not only the direct damage, but also the indirect effects of a nuclear war.

During the Cold War concern about the use of nuclear weapons initially concentrated on initial blast damage and the dangers of radioactive fallout. Subsequently, researchers began to explore the possible environmental effects of 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 suns 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 midlatitudes as a black particle cloud belt, blocking sunshine for several weeks.

The ensuing darkness and cold, combined with nuclear fallout radiation, would kill most of Earths 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 predicted 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 Earths surface.

Although the basic findings of the original TTAPS study have been confirmed by later reports, some later studies report a lesser degree of cooling would occur, 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 well below freezing over a majority of the densely inhabited areas of the Northern Hemisphere.

In contrast, some climate models posit a nuclear summer, predicting 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.

Opponents of the nuclear winter theory argue that there are many problems with the hypothesized scenarios either because of the models incorrect assumptions (e.g., the results would be right only if exactly the assumed amount of dust would enter the atmosphere, or because the model assumes uniformly distributed, constantly injected particles). Other critics of the nuclear winter scenario point out that the models used often to not include processes and/or feedback mechanisms that may moderate or mitigate the initial effects of nuclear blasts on the atmosphere (e.g., the moderating effects of the oceans).

The nuclear winter scenario remains scientifically controversial because the exact level of atmospheric damage, along with the extent and duration of subsequent processes cannot be agreed upon with full confidence.

What all scenarios and models forecast is that a nuclear war would have a significant effect on the atmosphere and climate of Earth, and consequently, would drastically and negatively affect many aspects of life such as food production and energy consumption. In any case, a global thermonuclear war would already have killed most human beings through the direct explosive effects of the weapons and the destruction of the foodproduction and distribution industries.

See also Atmospheric circulation.

Resources

PERIODICALS

Ehrlich, Paul, et al., LongTerm Biological Consequences of Nuclear War, Science 222, 4630 (1983).

Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, Carl Sagan, Nuclear Winter: Global Consequences of Multiple Nuclear Explosions, Science, 222, 4630 (1983).

Weinberger, Casper. The Potential Effects of Nuclear War on the Climate, Nuclear Winter, Joint Hearing before the Committee on Science and Technology and the Committee on Interior and Insular Affairs, U.S. House of Representatives. GPO 1985):274277.

White Paper. Nuclear Winter: Scientists in the Political Arena. Physics in Perspective. 3:1 (2001):76105.

Agnes Galambosi

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Nuclear Winter

Nuclear Winter

Introduction

Nuclear winter is a global climate event that could result from the prolonged use of nuclear weapons. The scenario was proposed in 1990 by several scientists, including the late American astronomer Carl Sagan (1934– 1996), who coined the term.

Nuclear winter refers to the cooling of Earth's climate that would be caused by the entry of smoke and soot into the atmosphere from the explosive power of many nuclear bombs during a conflict.

Although Sagan and the other original proponents of the nuclear winter scenario were initially motivated by an opposition to nuclear war, it has since been suggested that a similar sort of global climate change may have occurred in Earth's history because of the impact of large meteorites. In two known cases, the resulting climate change may have been so severe that many plant species and dinosaurs became extinct.

Historical Background and Scientific Foundations

During the 1950s and 1960s, political differences between the United States and the Union of Soviet Socialist Republics (now Russia) were so extreme that

both nations, while not actively warring with each other, were in a state of preparation for war. Part of this “Cold War” included the manufacture of nuclear weapons and the arming of long-distance missiles with nuclear pay-loads. Concern about the use of nuclear weapons originally concentrated on initial blast damage and the health dangers of radioactive fallout. Subsequently, researchers began to explore the possible environmental effects of nuclear war.

The concern with the possible environmental devastation of nuclear weapons had two origins. The first was the damage inflicted on the Japanese cities of Hiroshima and Nagasaki during World War II (1939–1945) with the detonation of two atomic bombs by the United States. By the 1950s and 1960s, the explosive power of atomic weapons had increased from those that leveled the Japanese cities, which were the equivalent of approximately 15,000 tons of dynamite, to about one million tons of dynamite (although some types of hydrogen bombs could generate an explosive force equivalent to 60 million tons of dynamite). Thus, the potential for damage had increased enormously, as had the stockpiles of nuclear weapons.

Secondly, scientists were aware of the climate influence of massive volcanic eruptions. In August 1883, for example, a series of huge eruptions of the Krakatoa volcano in Indonesia sent ash 50 mi (80 km) into the atmosphere. When ash was subsequently dispersed, the penetration of sunlight to Earth's surface was restricted. The average global temperature the year after the eruption was more than a degree Celsius below normal.

In the nuclear winter scenario, the explosion of dozens to hundreds of nuclear warheads would create huge fires in cities and forests. The resulting huge amounts of smoke and soot from burning cities and forests would drift up into the troposphere. This would block the sun's incoming radiation from reaching the surface of Earth, causing cooling of the surface temperatures. The smoke and soot 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 mid-latitudes of the Northern Hemisphere as a black particle cloud belt, blocking sunshine for several weeks.

The ensuing 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 tropo-sphere temperatures would rise because the smoke would absorb sunlight. The result would be a temperature inversion—a condition where the decrease in atmospheric temperature that occurs with increasing altitude is less than normal, or even increases with altitude. The inversion would trap smog close to the ground.

WORDS TO KNOW

AEROSOL: Particles of liquid or solid dispersed as a suspension in gas.

ATMOSPHERE: The air surrounding Earth, described as a series of shells or layers of different characteristics. The atmosphere— composed mainly of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases—acts as a buffer between Earth and the sun. The layers—troposphere, stratosphere, mesosphere, thermosphere, and the exosphere—vary around the globe and in response to seasonal changes.

OZONE LAYER: The layer of ozone that begins approximately 9.3 mi (15 km) above Earth and thins to an almost negligible amount at about 31 mi (50 km) and shields Earth from harmful ultra-violet radiation from the sun. The highest natural concentration of ozone (approximately 10 parts per million by volume) occurs in the stratosphere at approximately 15.5 mi (25 km) above Earth. The stratospheric ozone concentration changes throughout the year as stratospheric circulation changes with the seasons. Natural events such as volcanoes and solar flares can produce changes in ozone concentration, but man-made changes are of the greatest concern.

TROPOSPHERE: The lowest layer of Earth's atmosphere, ranging to an altitude of about 9 mi (15 km) above Earth's surface.

ULTRAVIOLET RADIATION: The energy range just beyond the violet end of the visible spectrum. Although ultraviolet radiation constitutes only about 5% of the total energy emitted from the sun, it is the major energy source for the stratosphere and mesosphere, playing a dominant role in both energy balance and chemical composition.

WATER VAPOR: The most abundant greenhouse gas, it is the water present in the atmosphere in gaseous form. Water vapor is an important part of the natural greenhouse effect. Although humans are not significantly increasing its concentration, it contributes to the enhanced greenhouse effect because the warming influence of greenhouse gases leads to a positive water vapor feedback. In addition to its role as a natural greenhouse gas, water vapor plays an important role in regulating the temperature of the planet because clouds form when excess water vapor in the atmosphere condenses to form ice and water droplets and precipitation.

Another predicted consequence is that nuclear explosions would produce nitrogen oxides, which are known to damage the protective ozone layer in the stratosphere. As a result of the depleted ozone, more ultraviolet radiation would reach Earth's surface. As ultraviolet radiation can damage genetic material, the number of cell changes (mutations) would increase. Although some mutations are harmless, others are not. For example, mutations that affect the ability of cells to control growth and division can result in the uncontrolled growth of the cells that is the basis of cancer.

Impacts and Issues

The original nuclear winter scenario of Sagan and his colleagues was vigorously debated at the time. Although the basic findings of the original study were confirmed by later modeling studies, other models indicated that the rate of surface cooling would be much less and would occur for only weeks, which would not be enough time to produce mass extinction of plants and animals.

Still other climate models indicate that rather than a post-nuclear war atmospheric cooling, Earth could experience a “nuclear summer,” predicting 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.

However, bolstering the concept of nuclear winter is the finding that on at least two occasions in Earth's history, the impact of huge meteorites (one was estimated to be about 6 mi [9.6 km] in diameter) may have caused mass extinctions in a nuclear winter-like fashion. Instead of smoke and soot, the meteorites caused impact debris to be circulated in the atmosphere. Indeed, one theory for the extinction of the dinosaurs is that atmospheric cooling after a meteorite impact changed the climate so abruptly that dinosaurs were unable to adapt.

Despite the controversy over nuclear winter, the various scenarios and models agree that a nuclear war would have a significant effect on the atmosphere and climate of Earth, and consequently, would drastically and negatively affect many aspects of life such as food production and energy consumption.

See Also Abrupt Climate Change; Aerosols; Atmospheric Pollution; Global Dimming.

BIBLIOGRAPHY

Books

DiMento, Joseph F. C., and Pamela M. Doughman. Climate Change: What It Means for Us, Our Children, and Our Grandchildren. Boston: MIT Press, 2007.

Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. New York: Rodale Books, 2006.

Periodicals

Basu, A. R., M. I. Petaev, R. J. Poreda, et al. “Chondritic Meteorite Fragments Association with the Permian-Triassic Boundary in Antarctica.” Science 302 (2003): 1388–1392.

Toon, O. B., A. Robock, R. P. Turco, et al. “Nuclear War: Consequences of Regional-Scale Nuclear Conflicts.” Science 315 (2007): 1224–1225.

Turco, R. P., O. B. Toon, T. P. Ackerman, et al. “Climate and Smoke: An Appraisal of Nuclear Winter.” Science 247 (1990): 166–176.

Web Sites

“Newton: Ask a Scientist. Global Warming/Nuclear Winter.” U.S. Department of Energy. <http://www.newton.dep.anl.gov/newton/askasci/1993/environ/ENV033.HTM> (accessed December 2, 2007).

Agnes Galambosi

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Nuclear Winter

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. 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.

During the Cold War concern about the use of nuclear weapons initially concentrated on initial blast damage and the dangers of radioactive fallout . Subsequently, researchers began to explore the possible environmental effects of 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 ensuing 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 predcited 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 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, 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 well below freezing over a majority of the densely inhabited areas of the Northern Hemisphere.

In contrast, some climate models postulate a '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.

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 because the model assumes uniformly distributed, constantly injected particles). Other critics of the nuclear winter scenario point out that the models used often to not include processes and/or feedback mechanisms that may moderate or mitigate the initial effects of nuclear blasts on the atmosphere (e.g., the moderating effects of the oceans).

The nuclear winter scenario remains scientifically controversial because the exact level of atmospheric damage, along with the extent and duration of subsequent processes cannot be agreed upon with full confidence.

What all scenarios and models forecast is that a nuclear war would have a significant effect on the atmosphere and climate of Earth, and consequently, would drastically and negatively affect many aspects of life such as food production and energy consumption.

See also Atmospheric circulation.

Resources

periodicals

Ehrlich, Paul, et al., "Long-Term Biological Consequences of Nuclear War." Science 222, 4630 (1983).

Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, Carl Sagan, "Nuclear Winter: Global Consequences of Multiple Nuclear Explosions," Science, 222,4630 (1983).

Weinberger, Casper. "The Potential Effects of Nuclear War on the Climate," Nuclear Winter, Joint Hearing before the Committee on Science and Technology and the Committee on Interior and Insular Affairs, U.S. House of Representatives. GPO 1985): 274-277.

White Paper. "Nuclear Winter: Scientists in the Political Arena." Physics in Perspective. 3:1 (2001):76-105.


Agnes Galambosi

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