Potentially lethal and destructive effects such as fire and blast may extend over ten miles in radius from the centre (ground-zero) of a nuclear explosion, while lethal levels of radio-active fallout dust would be deposited as far as 50 to 100 miles down-wind depending upon wind speed and local precipitation. The highly destructive nature of the nuclear weapons means that it is extremely difficult, and in most cases impossible to hit military targets without also devastating civilian habitations and environments nearby or down-wind. Evidence from Hiroshima and Nagasaki in Japan and from US atomic bomb tests established that long-term (20 to 30 years later) effects include eye cataracts, cancers of various types and impaired reproductive ability.
Thus the detonation of just one weapon in the megaton range over or near to a civilian centre of population would be a breach of the law on the following counts, inter alia: indiscriminate, unnecessary suffering, disproportionate force and lack of protection to civilians or injured non-combatants.
The detonation of up to 200 nuclear weapons in the 10 to 100 kiloton range on purely military targets in central Europe would result in 5-14 million deaths, primarily of civilians. Civilian casualties would exceed military casualties by a factor of 16 to 1. It was noted that in areas such as the Middle East or most of Europe, the use of even relatively few nuclear weapons - less than 0.1% of the current nuclear arsenals - would result in very high casualties. This is because in such areas military and civilian targets are highly interspersed. The legal provisions to protect property, buildings and undefended cities could not be kept. The possible erection of a so-called Star Wars or SDI (Strategic Defence Initiative) shield as envisaged at present would also not achieve the aim of separating civil and military targets. In the final or 'terminal' phase of such a putative shield, nuclear weapons would have to be destroyed in the atmosphere above cities and military bases. If these weapons were 'salvage fused', that is if they detonated with a nuclear explosion if hit, a most likely response to SDI, these low endo-atmospheric explosions would still cause severe blast and heat damage to cities. Weapons intercepted in the mid-course or this final phase would still deposit large quantities of highly radio-active elements and isotopes upon their intended targets.
Thus a 'limited' nuclear exchange would lead to a breach of the law on all the counts above, with the addition of the following: devastation of the environment and violation of neutrality (by fallout and blast). Countries such as Switzerland, Sweden and Hungary would suffer casualties to their populations, disruption of trade and imports and the poisoning of tracts of land making movement hazardous for many weeks and farming for up to a year.
Once nuclear weapons are used in larger quantities, that is up to 1-2% of the current arsenals, or even possibly at the 'tactical' level, a further effect of nuclear weapons becomes important. The heat of the nuclear fire-balls will start many fires creating huge clouds of smoke. These smoke clouds will merge and reduce the levels of light and heat from the sun and furthermore create a 'greenhouse' effect as with normal water vapour clouds. The result will be a general reduction of local and northern hemispheric average temperatures. If sufficient weapons are detonated, the resultant smoke particles could lead to the so-called 'nuclear winter' , in which light levels and land temperatures would be severely reduced for up to many months.
Causation of the nuclear winter would be an extreme violation of all the categories of the laws of war on every count. Countries very far removed from the theatres of war would suffer the most severe effects, leading to the starvation of estimated billions in the Third World as a result of crop and rains failure and world climatic catastrophe.