What would nuclear winter be like?

Debating the End of the World

London London
The notion of a nuclear winter wasteland may be terrifying, but is it realistic? Roland Shainidze Photography/Getty Images

­In many ways, the nuclear wint­er debate is similar to global warming debate. In both cases, it's easy to classify one side as alarmist and accuse the other of being in denial. It's also easy to attribute political motivations to either side.­

The atmosphere is an incredibly complicated system. When you have 5.5 quadrillion tons (4.99 quadrillion metric tons) of gas and countless local, global, terrestrial and extraterrestrial factors stirring it into motion, it's difficult to understand how it all works. Even advanced computer models lose effectiveness when forecasting weather more than a few days. The use of these models gave birth to the notion of chaos theory and the butterfly effect. The smallest change can have enormous consequences, and there's at least a hint of the unpredictable to everything.

During the 1970s, the National Academy of Sciences and the U.S. Office of Technology Assessment deliberated the possible environmental effects of nuclear war, and in 1982, the Swedish Academy of Sciences published "The Atmosphere after a Nuclear War: Twilight at Noon." This report predicted that smoke from burning cities and forests might diminish sunlight -- with dangerous consequences. In 1983, atmospheric scientist Richard Turco and astrochemist Carl Sagan joined three other scientists in publishing "Global Atmospheric Consequences of Nuclear Explosions." This article, known as the TTAPS report (short for the authors' names: Turco, Toon, Ackerman, Pollack and Sagan), generated a great deal of press. The United States and the Soviet Union gave the findings real consideration -- which some attribute to calming trigger fingers during the Cold War.

The TTAPS findings depend on 1980s computer weather models. But today, such technology is far from infallible. While most scientists agree that nuclear war would have some effect on the atmosphere, not everyone agrees on the severity. Author Michael Crichton accused the TTAPS authors of practicing "consensus science," in which speculation, public opinion and politics empower imperfect theories. Crichton argued that while consensus science may sell us something beneficial today, it sets a dangerous precedent for the future.

In 1990, the TTAPS authors published revised findings based on new data. The more moderate results appeased some critics, but there were -- and are -- still dissenting voices. These disagreements come down to four factors, each presenting its share of unknowns or unknowables:

  1. How much material is there to burn following a nuclear exchange?
  2. How much would remain in the atmosphere, and how much would fall back to the Earth's surface?
  3. How much sunlight would such smoke clouds deflect?
  4. During which season would the attack occur? If an attack occurred during the actual winter, might the results be far less severe?

As our understanding of the atmosphere improves, scientists continue to apply the data to the prospect of nuclear war. While it's easy to look at Cold War nuclear scenarios and discount nuclear winter as a threat in the 21st century, recent findings suggest we may be far from safe.

Using modern climate models, scientists Brian Toon and Alan Robock theorize that even a regional nuclear war could cause a marginal nuclear winter for everyone. According to their 2007 findings, if India and Pakistan were to each launch 50 nuclear weapons at each other, the entire globe could experience 10 years of smoke clouds and a three-year temperature drop of approximately 2.25 degrees F (1.25 degrees C) [source: Perkins]. Due in part to this report, the Bulletin of the Atomic Scientists advanced the Doomsday Clock two minutes closer to midnight.

­We're not a full century into the nuclear age, but so far we've avoided even regional nuclear war. Will this stalemate hold out? Or will humans eventually get to test nuclear winter theories firsthand?

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