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 18–65°F (10–35°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 (1934–1996). 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 25–75% 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 4–12°F (2–6°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 anomalies—possible leading to more human casualties globally than the direct effects of nuclear war—would 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): 271–274.

Overbye, D. "Prophet of the Cold and Dark." Discover (January 1985): 24–32.

Seitz, Russell. "An Incomplete Obituary." Forbes (February 10, 1997): 123–124.

Sinberg, Stan. "Springtime for Nuclear Winter." Omni (April 1992): 98–99.

Turco, R. P., et al. "Climate and Smoke: An Appraisal of Nuclear Winter." Science (January 12, 1990): 166–167.

ORGANIZATIONS

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