The Danger to the Human Race and the Earth
As long as nuclear weapons exist, the possibility of nuclear war remains. If nuclear weapons are used again, there can be no doubt that the damage will be dozens or hundreds of times greater than that inflicted on Hiroshima. Radioactive substances will be spread over vast areas, and millions of people will suffer radiation aftereffects far into the future. It is very likely that whole cities and surrounding forests will be set on fire. The soot and smoke from those fires will envelop the Earth, causing the Earth's climate to change. Some experts have predicted that nuclear war would lead to a "nuclear winter." Nuclear weapons continue to cast a dark shadow over the future of the human race.

Simulated temperature changes for 40 days after a nuclear war