While many a great invention and discovery happened in 20th century, there was a bleak side also. The use of nuclear energy for devastation will remain the biggest bane. The advent of nuclear weapons has transformed the conventional concept of warfare. In a nuclear war there are no victors, only the dead, while survivors will die a slow death. Indeed, technological advances in lethal nuclear bombs might not leave any survivor alive. Detonation of nuclear devices over just a few modern cities is likely to result in millions of deaths within the first few hours. And this could well be the least of the deadly afflictions. Several million more are likely to perish in the long-term damage that would result from the radioactivity unleashed by a nuclear explosion. It must be remembered that there is no civil defence to take care of the victims of nuclear explosion.

So far the only precedent of atomic devastation known to the mankind is the dropping of atom bombs over Hiroshima and Nagasaki. Compared to the highly lethal potential packed in today’s nuclear bombs these bombs seem harmful military toys. The atom bomb over Japan vitually atomised one lakh people. Today's "improved and researched" nuclear bombs, on an understated average, are 30 times more deadly.

The two Japanese towns, Hiroshima and Nagasaki, were sparsely populated with mostly single-storeyed structures. Today’s cities are thickly populated with multi-storeyed skyscrapers. This renders the post-nuclear scenario horribly frightening. According to a former scientific adviser to the British Prime Minister, even if a single nuclear device were to be exploded over a modern city, the blast would rip through skyscrapers turning vast panels and chunks of concrete and steel into high velocity secondary missiles that would smash their way for hundreds of yards in all directions.

The worst aftermath of a limited nuclear exchange would be the long-term collateral damage. Nuclear scientists in the West carried out experimental nuclear studies on about 1,600 acres of dead woodland. The smoke was propelled 6 km up into the atmosphere and the downwind carried the radioactive cloud over 100 km. A nuclear explosion over a city today would affect several thousand acres directly, reducting it instantly to smoking crater. The debris fireball would be propelled several miles right up to the stratosphere. This could blot out the sun for several days over vast stretches of land in the subcontinent.

God forbid, were this to happen, the average day temperature would fall by several degrees. This is called the nuclear winter. Studies by nuclear scientists in the southern hemisphere show that an extended average drop in temperature by 3-4 degree Celsius could destroy the wheat crop of the fertile eastern Indus plains and the Indo-Gangetic plains of the subcontinent. The radioactive fallout would result in several million slow and agonising deaths as the scientists put it. The only precedent of radioactive leak was the Chernobyl nuclear plant accident in the erstwhile USSR. It was a thousandth fraction of the radioactive fallout over Chernobyl that drifted all the way to Europe and reached right up to the coast of the US. A nuclear war is an altogether different genre from conventional wars.

The conventional planning of war, where civil defence is organised to mitigate the aftermath of bombing, would not work. The Chernobyl accident overstretched the entire civil defence and emergency resources of the Soviet Russia. The Soviet scientist in-charge of the clean-up admitted that it cost their country billions. One can only shudder to imagine the radioactive fallout from several thousand Chernobyls exploding at the same time. The London civic authorities were asked to prepare civil defence plans for a limited nuclear exchange at the height of the Cold War. The authorities came to the conclusion that to talk of civil defence plans in such a scenario would be a cruel deception on the civilian population.

All the long-term damaging effects of nuclear radiation have not been definitively studied, even in the West. Scientists confirm that genetic mutation is a frightful prospect and the human immune system would be damaged. A detonation over a nuclear power reactor could poison the soil and the underground aquifers for hundreds or thousands of years, leading US nuclear scientist Carl Sagan warns us. A deadly fallout of a nuclear explosion over a crowded modern city is likely to result in inadvertent chemical mass murder. Most modern buildings today use large quantities of synthetic material and plastic. A nuclear explosion would set off pyrotoxins, particularly the deadly gamma ray. This is an invisible pyrotoxin capable of penetrating one-foot thick concrete. It is capable of frying the human flesh instantly. The explosion would simultaneously generate a pall of deadly asbestos fibres from high-rise building insulated with it. The fine asbestos fibre would drift over large areas exposing multitudes to the long-term prospect of a deadly form of cancer, says Carl Sagan.