What is nuclear winter?

Question

What is nuclear winter?

Answer 1

Though not in the public's consciousness as much since the Cold War came to a close around 1989 and the break up of the Soviet Union in 1991, the possibility of nuclear war exists as long as the weapons themselves do.

The effects of a nuclear exchange are well known: many films and books are devoted to elucidating the damage done to people, buildings, and the environment by a nuclear blast. But researchers focusing on climate have theorized the dire effects of such a war upon the climate may be just as bad or worse.

Carl Sagan, and other authors introduced the idea of "Nuclear Winter" in a 1983 scientific journal article (Science, Dec. 1983, pg. 1283). In the theory of Nuclear Winter, after the explosions of a nuclear exchange have died down--the spread of smoke in the atmosphere from nuclear-started fires, could absorb sunlight, darken the sky and ultimately lower the temperature of the Earth from 1 to 5 degrees Centigrade within a few months.

The models in this study further show that a change in the temperature of even one (1) degree Centigrade (which may not sound like much) could unbalance the ecosystem and affect the survival of many species on Earth, including mankind.

The idea of the effects of too much smoke in the sky are not just an idle theory either--something similar may have already happened in the Earth's past, at the end of the Cretaceous period some 65 million years ago.

In 1979, a researcher named Walter Alvarez was sifting through sediments from Gubbio, Italy when he discovered a surplus of a radio-active element--called iridium--in sediments dating back to the boundary between the Cretaceous and Tertiary periods (called the K-T boundary). This iridium did not have an easy terrestrial explanation.

Alvarez’s research gave support to an already proposed asteroid theory of dinosaur extinction that figures in many films, including Disney's "Dinosaur." This theory suggests that a large meteorite hit the Earth around 65 million years ago, causing fires. This meteor would explain the iridium deposits and the fires would explain a surplus of carbon that has also been discovered at the K-T boundary layer. Scientists know that iridium is much more common in asteroids and meteors than it is on Earth.

Other researchers studying carbon deposits in sedimentary layers have documented a period in Earth’s past when ancient wildfires were widespread. Did these “ancient wildfires” lead to the extinction of the Dinosaurs? Fossils in the sediments in the K-T boundary also show a strange disappearance of about 50 percent of the genera in this period of time.

These ancient fires may provide evidence from Earth's past that give us an idea of how a nuclear war climate might affect the climate. It would be hard to prepare for the striking of an asteroid, though in Hollywood films mankind always gets together to defeat even such a random event.

But we can all hope that nuclear war, depending as it does on the hatreds and fears of mankind, will never be quite so random.

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Answer 2

Nuclear winter is a hypothetical global climate condition that is predicted to be a possible outcome of a large-scale nuclear war. It is thought that severely cold weather can be caused by detonating large numbers of nuclear weapons, especially over flammable targets such as cities, where large amounts of smoke and soot would be injected into the Earth's stratosphere. The term has also been applied to one of the after-effects of a comet or asteroid impact[1][2], also sometimes termed an impact winter, or of a supervolcano eruption.[3]

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Answer 3

The nuclear winter scenario predicts that the huge fires caused by nuclear explosions (particularly from burning urban areas) would deliver large quantities of aerosol particles into the stratosphere, where they could remain for months or years, and which would significantly reduce the amount of sunlight that reached the surface. The ash and dust would be carried by the midlatitude west-to-east winds, forming a uniform belt of particles encircling the northern hemisphere from 30°N to 60°N latitudes (assuming most targets in a nuclear exchange are located between these latitudes). The dust clouds would then block out much of the sun's light, causing surface temperatures to drop drastically.