The tangible impact of the atomic explosions in Hiroshima and Nagasaki on the survivors from these two historical explosions was limited. They receive medical treatment and other assistance from out side. But the intangible impact was more severe: A serious negative impact on the environment that caused famine, diseases, pollution everywhere and climate changes.

What may happen if a nuclear war broke down now anywhere in the Earth will be mire serious than it may be expected.
Eventually, in a try to prevent any nuclear war to break down again in the future, many scientists tried to picture some of what may happen if this nuclear war really took place:
In the aftermath of a large-scale war in which nuclear weapons were exploded in major cities, darkened skies would cover large areas of the Earth for perhaps weeks or several months, because sunlight was blocked by the massive clouds of smoke formed by the act of widespread fires. A radical change would happen in the entire Earth’s climate especially in the Northern Hemisphere. Average temperature might fall some tens of degrees below zero because all the sun heat is blocked by the smoke clouds. Climatic disturbance might persist for several years, even in countries that are not directly involved in the nuclear war.

As a normal consequence for these radical climatic changes, crops would be destroyed. The whole world would face a fatal famine. World agriculture and major ecosystem, forests, grasslands and marine system, would be ruined. Other impacts could include severe disruptions of communications and power systems; reductions in the ozone layer in the upper atmosphere which protects life on Earth from harmful sun radiation; intense local and long-term global fallout; and severe regional episodes of air and water pollution caused by the release of large amounts of toxic gases and chemicals.
In short; in the aftermath of a real nuclear war the global environment and the human social and economic systems could collapse to a real extent.

Click here to watch video clip about the atomic bomb that was dropped by the United States during World War II on Hiroshima, Japan, August 6, 1945.