The Cold War ended in 1989. But still both the U.S. and Russia have 3,000 nuclear missiles each on hair-trigger alert, pointed at 240 major metropolitan areas in the northern hemisphere. According to scientific analysis if 1,000 bombs are dropped on 100 cities, such a pall of black, radioactive, oily smoke will be created that it will cover the earth for a year, block out the sun, and produce nuclear winter and bring life on earth to an end. The fact is we are continually on the brink of nuclear war and annihilation.
 What is Nuclear Winter
Nuclear winter is a hypothetical set of circumstances on a likely global climate condition that would follow a large-scale nuclear war. Carl Sagan and other authors introduced the idea of "Nuclear Winter" in a 1983 scientific journal article (Science, Dec. 1983, pg. 1283) where they predicted that following a war, the smoke from the nuclear-exchanged fire would spread and absorb sunlight, darken the sky and ultimately lower the temperature of the earth within a few months. Large quantities of aerosol particles dispersed into the atmosphere could potentially remain in the stratosphere for months or even years.
A large nuclear bomb bursting at ground level would throw up about a million tonnes of dust and block out a large fraction of the sunlight and the sun's heat from the earth's surface. The earth would quickly become dark and cold. Temperatures would drop by something in the region of 10-20ºC. It would take months for the sunlight to get back to near normal. The drop in light and temperature would quickly kill crops and other plant and animal life while humans would be affected by very large-scale malnutrition and disease.
Bombs bursting over cities and surface installations, like factories or oil stores and refineries, would cause huge fires and fire-storms that would send huge amounts of smoke into the air.
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 Huge Temperature Inversion
While the nuclear exchanges would lower the temperature at the surface, the upper part of the troposphere (5-11 km) would see a rise in temperature because of sunlight absorbed by the smoke. This would cause a huge temperature inversion and keep many other pollutants produced by widespread fires (e.g. dioxins, PCBs, sulfurous gases) down at the levels people breathe.
The high levels of nitrogen oxides would also cause widespread destruction of the ozone layer. The average loss of ozone could be as much as 70%. As a result increased UV radiation would reach the earth's surface, causing immense harm to humans and other living things, notably sensitive plankton, which is at the bottom layer of the whole marine food chain.
 Hiroshima and Nagasaki
It has been pointed out that even a fall in temperature by 1 degree Centigrade could unbalance the ecosystem and threaten the existence of many species, including man. As they were air bursts, the full implications of the radioactive fallout of the explosions at Hiroshima and Nagasaki were not realized till the atmospheric testing of hydrogen bombs in the 1950s. It was realized only in the 1970s that nuclear explosions could inject large amounts of nitrogen oxides into the stratosphere, acting as a catalyst to reduce ozone levels and thereby allow increased amounts of ultraviolet light to penetrate to the earth's surface
Nuclear winter would cause an ecological disaster of a magnitude similar to the major extinctions of the past, such as what happened at the end of the Cretaceous period 65 million years ago when 75% of all species died out, including the dinosaurs. An added factor after a nuclear war would be radioactive contamination giving worldwide background radiation doses many times larger than what has ever happened during the 3 billion years of evolution.
 New Thoughts on Nuclear Winter
As small-scale nuclear exchanges are today more likely than the massive US-Soviet exchanges feared during the Cold War, a recent study has revealed that even such exchanges of nuclear weapons could result in a decade-long "nuclear winter", and destroy agriculture and millions of lives.
Using modern and vastly improved climate models and taking small-scale nuclear wars into account, Brian Toon, head of atmospheric and oceanic sciences at the University of Colorado at Boulder, and Alan Robock of Rutgers University in New Jersey, both in the US, predict less but longer cooling than previously anticipated, but with potentially more devastating consequences.
It is also said that about 40 countries possess enough plutonium or uranium to construct substantial nuclear arsenals. Setting off a Hiroshima-size weapon could cause as many direct fatalities as all of World War II. The impact of such an encounter would be global, probably plunging the planet into a "nuclear winter" and blanketing wide areas of the world with radioactive fallout.
 How We Can Survive a Nuclear Winter
Dealing with UV radiation
Ozone depletion will bring in abundance of UV radiation into our atmosphere which can cause eye damage and skin cancer
Here are some things to consider
• Protect against UV exposure by covering yourself from head to toe. This will provide protection to your skin.
• Put on a hat and remain as long as possible in the shade.
• Use a high UV protection factor sunscreen
• Protect your eyes with sunglasses or lab safety glasses
• As children are more susceptible to UV radiation give them added protection
Dealing with the cold
Here are some ways of dealing with a longstanding cold spell
• Keep emergency heating supplies ready - Remember that in the event of a nuclear war the first things to go off would be electric, gas and oil. It is, therefore, advisable to have a stove and a surplus of firewood at your home.
• Keep all the necessary clothing on hand – Instead of wearing one thick layer, put on several layers of light clothing as the extra layers allow easier movement. Moreover, dispersion of perspiration is easier with more layers.
• Keep ready boots, gloves, and sunglasses / goggles - Though northerners would obviously do this, a nuclear winter could also reach those in warmer climates and not accustomed to such weather.
• Produce your own food
A longstanding nuclear would definitely adversely affect our ability to grow food.
It will, therefore, become vital to find ways of producing our own food. For the initial period it is advisable to store a large amount of non perishable food and water on hand which would come in handy during any emergency. Refer to this site for details WHAT TO DO IF A NUCLEAR DISASTER IS IMMINENT! 
See video on You Tube Nuclear Winter