A nuclear bomb has certain special characteristics that distinguish it from a conventional weapon and make the effects of this weapon particularly devastating in terms of immediate casualties and longer-term health and environmental impact.
These unique characteristics are:
The explosion of a nuclear bomb over a target such as a populated city would lead to immense and severe damage. The degree of damage would depend upon the distance from the centre of the bomb blast, which is called the hypocentre or ground zero. The closer one is to the hypocentre, the more severe the damage.
Although the exact number of dead and injured will never be known, the estimated death toll is staggering. It ranges between 100,000 and 180,000 for Hiroshima, and between 50,000 and 100,000 for Nagasaki.
Causes of death were numerous and these included burning, being crushed by falling debris and radiation.
The Hiroshima health department estimated the proportion of deaths from burns to be 60%, deaths from falling debris to be 30% and deaths from other injuries such as radiation to be 10%.
Immediately after the detonation the temperature at the centre of the fireball is several million degrees Celsius.
Survivors in the two cities stated that people who were in the open directly under the explosion of the bomb were so severely burned that the skin was charred dark brown or black and that they died within a few minutes or hours.
In Hiroshima the atomic bomb exploded close to the centre of the city and 90% of buildings collapsed or burned. Thousands of people were pinned beneath the debris. Many were able to escape or received aid in escaping, but large numbers succumbed either to their injuries or to fire before they could escape
Our understanding of radiation casualties is not complete. In the words of Dr. Robert Stone of the Manhattan Project, "The fundamental mechanism of the action of radiation on living tissues has not been understood.”
Radiation victims who were near the hypocentre but escaped heat burns or secondary injuries became ill within two or three days with symptoms such as nausea, vomiting, bloody diarrhoea and hair loss. Most died within a week.
Radiation victims who were further away from the explosion did not show severe symptoms until later (one to four weeks after the explosion). The first signs were loss of appetite, lassitude and general discomfort. Inflammation of the gums, mouth, and pharynx as well as fever appeared next.
Radiation caused a wide range of disorders for decades. Even today, after more than fifty years, the full range of effects of radiation taken into the body has yet to be clarified. Many survivors continue to suffer from those effects.
The atomic bomb had serious effects on foetuses. Many were stillborn, and exposed foetuses born alive had higher infant mortality rates than other children. Children who were born also suffered an increased incidence of a syndrome characterized by an abnormally small skull, accompanied in severe cases by mental disabilities.
Beginning around 1960, the incidence of cancer began to increase. The main cancers included thyroid, breast, lung, and salivary gland. The role of radiation in cancer is significant. Some researchers reported a direct correspondence between distance from hypocenter, probable exposure dose, and malignancy rates.
Nuclear weapons cause severe damage to the environment and it is suspected that no other weapon is capable of causing environmental damage on a similar scale.
In 1987 the World Commission on the Environment and Development described the likely consequences of nuclear war as:
"making other threats to the environment pale into insignificance. One thermo-nuclear bomb [hydrogen bomb] can have an explosive power greater than all the explosives used in wars since the invention of gunpowder. In addition to the destructive effects of blast and heat, immensely magnified by these weapons, they introduce a new lethal agent -ionising radiation- that extends lethal effects over both space and time." (Tri-Denting It Handbook, p.94)
A certain effect of the massive exchange of nuclear weapons is the nuclear winter. A nuclear winter would arise as a result of hundreds of millions of tons of soot in the atmosphere from fires in cities, in forests and in the countryside, caused by nuclear weapons. The smoke cloud and debris from multiple explosions could blot out sunlight, leading to crop failures throughout the world and starvation.