Nuclear Winter

What is it?

A period of abnormally cold and darkness predicted to follow a nuclear war, caused by a layer of smoke and dust in the atmosphere blocking the sun's rays.

What would happen?

In the aftermath of a 5,000 MT nuclear exchange, survivors would face extreme cold, water shortages, lack of food and fuel, heavy burdens of radiation and pollutants, diseases, and severe psychological stress – all in twilight or darkness. It is clear that the ecosystem effects alone resulting from a large-scale thermo-nuclear war would be enough to destroy civilisation as we know it in at least the Northern Hemisphere. These long-term effects, when combined with the direct casualties from the blast, suggest that eventually there might be no human survivors in the Northern Hemisphere. Human beings, other animals, and plants in the Southern Hemisphere would also suffer profound consequences.
Timeline of International Nuclear Weapons Testing
How to survive nuclear winter long term?
Some scientists predict that nuclear winter would be followed by an even harsher spring. They theorize that the sunlight bounced back up from the smoke clouds would heat up nitrogen oxides in the stratosphere. At high temperatures, the nitrogen oxides, which formed due to blast-burned oxygen, would deplete the ozone layer at much higher than normal rates.
On the 8th Day - Nuclear Winter Documentary (1984)
Scientists at the conference estimated that just eight days after a nuclear attack, world temperatures would have collapsed with even sub-Saharan Africa and the Amazon Basin experiencing daytime temperatures that would hover around the zero degrees Celsius mark.