This page provides general information about the development of nuclear weapons, disarmament and non-proliferation efforts.

What are nuclear weapons?

Nuclear weapons, like conventional bombs, are designed to cause damage through an explosion. In conventional bombs the explosion is created by a chemical reaction, which involves the rearrangement of atoms to form new molecules, whereas in nuclear weapons the explosion is created by changing the atoms themselves - they are either split or fused to create new atoms. The explosive power of a nuclear weapon is generated by the process of nuclear fission (an atomic bomb) or nuclear fusion (a hydrogen or thermonuclear bomb). They are classified as either "strategic weapons"—which are used to strike targets deep inside enemy territory—or "tactical weapons"—short-range weapons designed to destroy specific military, communications or infrastructure targets on the battlefield.

Mushroom Cloud (Photo: U.S. Army)
Mushroom Cloud (Photo: U.S. Army)

What happens when a nuclear weapon explodes?

A nuclear explosion produces several forms of damaging effects: blast, thermal radiation, electromagnetic pulse, direct nuclear radiation and fallout. Depending on the size of the nuclear weapon, the height at which it was detonated and the geography of the target, damage by the bomb will vary. In the case of the atomic bombs dropped on Hiroshima and Nagasaki, upon detonation, the explosion created a fireball of white heat. Intense heat and radiation was released in winds of around 1,500 kmph. Under these extreme conditions, human bodies were vaporized and those not in the immediate area of destruction suffered from non-survivable burns, were blinded and suffered terrible external and internal injuries. In addition, radiation from the radioactive material caused by the bomb has been linked to chromosomal damage and illnesses such as cancer that can continue to affect generations of family members. Since the end of World War II, over 280 nuclear weapons have been tested in the Pacific region alone, each possessing much higher yields than the bombs dropped on Hiroshima and Nagasaki.

Hibakusha (atomic bomb survivor) at quarantine station suffering from severe burns all over his body (Hiroshima Peace Memorial Museum)
Hibakusha (atomic bomb survivor) at quarantine station suffering from severe burns all over his body (Hiroshima Peace Memorial Museum)

Damage Caused by Nuclear Testing and General Nuclear-Related Damage

How many nuclear weapons exist today?

The Stockholm International Peace Research Institute (SIPRI) reports in its 2011 Yearbook that there are about 20,500 nuclear warheads, enough to destroy all life on Earth many times over. Currently, several thousand of these nuclear weapons are kept on high alert, ready to be launched within minutes. Once these weapons are launched they cannot be recalled. As long as these weapons continue to exist, human security remains at risk.

SIPRI report

For more information on the history of the development and usage of nuclear weapons, in addition to international efforts toward disarmament and non-proliferation, see

Timeline of the Nuclear Age

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