Nuclear holocaust refers to the possibility of nearly complete annihilation of human civilization by 

nuclear warfare. Under such a scenario, all or most of the Earth is made uninhabitable by nuclear weapons in future world wars.

A common definition of the word "holocaust": "great destruction resulting in the extensive loss of life, 

especially by fire."^[1] The word is derived from theGreek term "holokaustos" meaning "completely burnt." Po

ssibly the first printed use of the word "holocaust" to describe an imagined nuclear destruction is Regi

nald Glossop's 1926: "Moscow ... beneath them ... a crash like a crack of Doom! The echoes of this Holocaust rumbled and rolled ... a distinct 

smell of sulphur ... atomic destruction."

^[2] In the 1960s the principal referent of the unmodified "holocaust" was nuclear destruction.^[3] Since the mid 1970s the capitalized term "Holocaust" has been closely associated with the Nazi mass slaughter of Jews (see Holocaust) and "holocaust" in its nuclear destruction sense is almost always preceded by "atomic" or "nuclear".^[4]

Nuclear physicists and authors have speculated that nuclear holocaust could result in an end to human life, or at

 least to modern civilization on Earth due to the immediate effects of nuclear fallout, the loss of much modern technology due to electromagnetic pulses, or nuclear winter and resulting extinctions.

Nuclear warfare, or atomic warfare, is a military conflict or political strategy in which nuclear weapons are

 used. Compared to conventional warfare, nuclear warfare is vastly more destructive in range and extent of damage. A major nuclear exchange could have severe long-term effects, primarily from radiation release but also

 from possible atmospheric pollution leading to nuclear winter, that could last for decades, centuries, or even millennia after th

e initial attack.^[1][2] Nuclear war is considered to

 bear existential risk for civilization on Earth.^[3][4]

The first, and to date only, nuclear war was the atomic bombings of Hiroshima and Nagasaki, Japan by the United States shortly before the end of World War II.^[5][6]At the time of those bombings, the United

 States was the only country to possess atomic weapons. After World War II, nuclear weapons were also developed by theUnited Kingdom, France, the Soviet Union, and the People's Republic of China, which contributed to the state of conflict and tension that became known as theCold War. In the 1970s, India and 1990s, Pakistan, countries openly hostile to each other, developed nuclear weapons.

After the collapse of the Soviet Union in 1991 and the resultant end of the Cold War, the threat of a major nuclear wa

r between the superpowers was generally thought to have receded. Since then, concern over nuclear weapons has

 shifted to the prevention of localized nuclear conflicts resulting from nuclear proliferation, and the threat of 

nuclear terrorism.

The Doomsday Clock is a symbolic clock face, maintained since 1947 by the board of directors of the

 

Bulletin of the Atomic Scientists at the University of Chicago, that uses the analogy of the human species being at a 

time that is "minutes to midnight", wherein midnight represents "catastrophic destruction". Originally, the analogy represented the threat of global nuclear war, but since includes climate-

changing technologies and "new developments in the life sciences and nanotechnology tha

t could inflict irrevocable harm".^[1] The closer the clock is to midnight, the closer the world is estimated to be to global disaster.

Since its inception, the clock has appeared on every cover of the Bulletin of the Atomic Scientists. Its first representation was in 1947, when magazine co-founder Hyman Goldsmith asked artist Martyl Langsdorf (wife of 

Manhattan Project physicist Alexander Langsdorf, Jr.) to design a cover for the magazine's June 1947 issue.

The number of minutes before midnight – measuring the degree of nuclear, environmental, and technological threats to mankind – is periodically corrected; currently, the clock reads five minutes to midnight, having advanced two minutes on 17 January 2007.