World War III

From Wikipedia, the free encyclopedia

Nuclear warfare is a common theme of World War III scenarios. Such a conflict has been hypothesised to result in human extinction.

 

World War III (WWIII or WW3) and the Third World War are names given to a hypothetical third worldwide large-scale military conflict subsequent to World War I and World War II. The term has been in use since at least as early as 1941. Some have applied it loosely to refer to limited or smaller conflicts such as the Cold War or the War on Terror, while others assumed that such a conflict would surpass prior world wars both in its scope and in its destructive impact.

Due to the development and use of nuclear weapons near the end of World War II and their subsequent acquisition and deployment by many countries, the potential risk of a nuclear devastation of Earth's civilization and life is a common theme in speculations about a Third World War. Another major concern is that biological warfare could cause a very large number of casualties, either intentionally or inadvertently by an accidental release of a biological agent, the unexpected mutation of an agent, or its adaptation to other species after use. High-scale apocalyptic events like these, caused by advanced technology used for destruction, could potentially make the Earth's surface uninhabitable. 

Prior to the beginning of the Second World War, the First World War (1914–1918) was believed to have been "the war to end all wars," as it was popularly believed that never again could there possibly be a global conflict of such magnitude. During the interwar period, WWI was typically referred to simply as "The Great War." The outbreak of World War II in 1939 disproved the hope that mankind might have already "outgrown" the need for such widespread global wars.

With the advent of the Cold War in 1945 and with the spread of nuclear weapons technology to the Soviet Union, the possibility of a third global conflict became more plausible. During the Cold War years, the possibility of a Third World War was anticipated and planned for by military and civil authorities in many countries. Scenarios ranged from conventional warfare to limited or total nuclear warfare. At the height of the Cold War, a scenario referred to as Mutually Assured Destruction ("MAD") had been calculated which determined that an all-out nuclear confrontation would most certainly destroy all or nearly all human life on the planet. The potential absolute destruction of the human race may have contributed to the ability of both American and Soviet leaders to avoid such a scenario.

Coinage

Time magazine

Time magazine was an early adopter if not originator of the term "World War III". Perhaps the first usage appears in its 3 November 1941, issue (preceding the Japanese attack on Pearl Harbor on 7 December 1941) under its "National Affairs" section and entitled "World War III?" about Nazi refugee Dr. Hermann Rauschning, who had just arrived in the United States. In its 22 March 1943, issue under its "Foreign News" section, Time reused the same title "World War III?" with regard to statements by then-U.S. Vice President Henry A. Wallace: "We shall decide some time in 1943 or 1944 ... whether to plant the seeds of World War III." Time continued to entitle with or mention in stories the term "World War III" for the rest of the decade (and onwards): 1944, 1945, 1946 ("bacterial warfare"), 1947, and 1948. (Time persists in using this term, e.g., this 2015 book review, entitled "This Is What World War III Will Look Like.")

Military plans

Military planners have been war gaming various scenarios, preparing for the worst, since the early days of the Cold War. Some of those plans are now out of date and have been partially or fully declassified.

Operation Unthinkable

British Prime Minister Winston Churchill was concerned that, with the enormous size of Soviet forces deployed in Europe at the end of WWII and the unreliability of the Soviet leader Joseph Stalin, there was a serious threat to Western Europe. In April–May 1945, British Armed Forces developed Operation Unthinkable, thought to be the first scenario of the Third World War. Its primary goal was "to impose upon Russia the will of the United States and the British Empire". The plan was rejected by the British Chiefs of Staff Committee as militarily unfeasible.

Operation Dropshot

"Operation Dropshot" was the 1950s United States contingency plan for a possible nuclear and conventional war with the Soviet Union in the Western European and Asian theaters.

At the time the US nuclear arsenal was limited in size, based mostly in the United States, and depended on bombers for delivery. "Dropshot" included mission profiles that would have used 300 nuclear bombs and 29,000 high-explosive bombs on 200 targets in 100 cities and towns to wipe out 85% of the Soviet Union's industrial potential at a single stroke. Between 75 and 100 of the 300 nuclear weapons were targeted to destroy Soviet combat aircraft on the ground.

The scenario was devised prior to the development of intercontinental ballistic missiles. It was also devised before U.S. President John F. Kennedy and his Secretary of Defense Robert McNamara changed the US Nuclear War plan from the 'city killing' countervalue strike plan to a "counterforce" plan (targeted more at military forces). Nuclear weapons at this time were not accurate enough to hit a naval base without destroying the city adjacent to it, so the aim in using them was to destroy the enemy industrial capacity in an effort to cripple their war economy.

Exercises Grand Slam, Longstep, and Mainbrace

In January 1950, the North Atlantic Council approved NATO's military strategy of containment. NATO military planning took on a renewed urgency following the outbreak of the Korean War in the early 1950s, prompting NATO to establish a "force under a centralised command, adequate to deter aggression and to ensure the defence of Western Europe". Allied Command Europe was established under General of the Army Dwight D. Eisenhower, US Army, on 2 April 1951. The Western Union Defence Organization had previously carried out Exercise Verity, a 1949 multilateral exercise involving naval air strikes and submarine attacks.

Exercise Mainbrace brought together 200 ships and over 50,000 personnel to practice the defence of Denmark and Norway from Russian attack in 1952. It was the first major NATO exercise. The exercise was jointly commanded by Supreme Allied Commander Atlantic Admiral Lynde D. McCormick, USN, and Supreme Allied Commander Europe General Matthew B. Ridgeway, US Army, during the autumn of 1952.

The US, UK, Canada, France, Denmark, Norway, Portugal, Netherlands, and Belgium all participated. 

Exercises Grand Slam and Longstep were naval exercises held in the Mediterranean Sea during 1952 to practice dislodging an enemy occupying force and amphibious assault. It involved over 170 warships and 700 aircraft under the overall command of Admiral Carney. The overall exercise commander, Admiral Carney summarized the accomplishments of Exercise Grand Slam by stating: "We have demonstrated that the senior commanders of all four powers can successfully take charge of a mixed task force and handle it effectively as a working unit."

The USSR called the exercises "war-like acts" by NATO, with particular reference to the participation of Norway and Denmark, and prepared for its own military maneuvers in the Soviet Zone.

Operation Strikeback

This was a major NATO naval exercise held in 1957, simulating a response to an all-out Soviet attack on NATO. The exercise involved over 200 warships, 650 aircraft, and 75,000 personnel from the United States Navy, the United Kingdom's Royal Navy, the Royal Canadian Navy, the French Navy, the Royal Netherlands Navy, and the Royal Norwegian Navy. As the largest peacetime naval operation up to that time, Operation Strikeback was characterized by military analyst Hanson W. Baldwin of The New York Times as "constituting the strongest striking fleet assembled since World War II".

Exercise Reforger

If activated, Operation Reforger would have largely consisted of convoys like this one from Operation Earnest Will in 1987, although much larger. While troops could easily fly across the Atlantic, the heavy equipment and armor reinforcements would have to come by sea.

 

Exercise Reforger (from return of forces to Germany) was an annual exercise conducted, during the Cold War, by NATO. The exercise was intended to ensure that NATO had the ability to quickly deploy forces to West Germany in the event of a conflict with the Warsaw Pact. The Warsaw Pact outnumbered NATO throughout the Cold War in conventional forces, especially armor. Therefore, in the event of a Soviet invasion, in order not to resort to tactical nuclear strikes, NATO forces holding the line against a Warsaw Pact armored spearhead would have to be quickly resupplied and replaced. Most of this support would have come across the Atlantic from the US and Canada.

Reforger was not merely a show of force—in the event of a conflict, it would be the actual plan to strengthen the NATO presence in Europe. In that instance, it would have been referred to as Operation Reforger. Important components in Reforger included the Military Airlift Command, the Military Sealift Command, and the Civil Reserve Air Fleet.

Seven Days to the River Rhine

A Warsaw Pact invasion would have come via three main paths through West Germany.

 

Seven Days to the River Rhine was a top-secret military simulation exercise developed in 1979 by the Warsaw Pact. It started with the assumption that NATO would launch a nuclear attack on the Vistula river valley in a first-strike scenario, which would result in as many as two million Polish civilian casualties. In response, a Soviet counter-strike would be carried out against West Germany, Belgium, the Netherlands and Denmark, with Warsaw Pact forces invading West Germany and aiming to stop at the River Rhine by the seventh day. Other USSR plans stopped only upon reaching the French border on day nine. Individual Warsaw Pact states were only assigned their own subpart of the strategic picture; in this case, the Polish forces were only expected to go as far as Germany. The Seven Days to the Rhine plan envisioned that Poland and Germany would be largely destroyed by nuclear exchanges, and that large numbers of troops would die of radiation sickness. It was estimated that NATO would fire nuclear weapons behind the advancing Soviet lines to cut off their supply lines and thus blunt their advance. While this plan assumed that NATO would use nuclear weapons to push back any Warsaw Pact invasion, it did not include nuclear strikes on France or the United Kingdom. Newspapers speculated when this plan was declassified, that France and the UK were not to be hit in an effort to get them to withhold use of their own nuclear weapons.

Exercise Able Archer

President Ronald Reagan and Soviet double agent Oleg Gordievsky, who later told the west how close the Able Archer 83 exercise had brought the Soviets to ordering a First Strike.

 

Exercise Able Archer was an annual exercise by the United States military in Europe that practised command and control procedures, with emphasis on the transition from solely conventional operations to chemical, nuclear, and conventional operations during a time of war. 

"Able Archer 83" was a five-day North Atlantic Treaty Organization (NATO) command post exercise starting on 7 November 1983, that spanned Western Europe, centered on the Supreme Headquarters Allied Powers Europe (SHAPE) Headquarters in Casteau, north of the city of Mons. Able Archer exercises simulated a period of conflict escalation, culminating in a coordinated nuclear attack.

The realistic nature of the 1983 exercise, coupled with deteriorating relations between the United States and the Soviet Union and the anticipated arrival of strategic Pershing II nuclear missiles in Europe, led some members of the Soviet Politburo and military to believe that Able Archer 83 was a ruse of war, obscuring preparations for a genuine nuclear first strike. In response, the Soviets readied their nuclear forces and placed air units in East Germany and Poland on alert. This "1983 war scare" is considered by many historians to be the closest the world has come to nuclear war since the Cuban Missile Crisis of 1962. The threat of nuclear war ended with the conclusion of the exercise on 11 November, however.

Strategic Defense Initiative

The Strategic Defense Initiative (SDI) was proposed by U.S. President Ronald Reagan on 23 March 1983. In the latter part of his presidency, numerous factors (which included watching the 1983 movie The Day After and hearing through a Soviet defector that Able Archer 83 almost triggered a Russian first strike) had turned Ronald Reagan against the concept of winnable nuclear war, and he began to see nuclear weapons as more of a "wild card" than a strategic deterrent. Although he later believed in disarmament treaties slowly blunting the danger of nuclear weaponry by reducing their number and alert status, he also believed a technological solution might allow incoming ICBMs to be shot down, thus making the US invulnerable to a first strike. However, the USSR saw the SDI concept as a major threat, since a unilateral deployment of the system would allow the US to launch a massive first strike on the Soviet Union without any fear of retaliation. 

The SDI concept was to use ground-based and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic offense doctrine of Mutual Assured Destruction (MAD). The Strategic Defense Initiative Organization (SDIO) was set up in 1984 within the United States Department of Defense to oversee the Strategic Defense Initiative.

NATO nuclear sharing

NATO operational plans for a Third World War have involved NATO allies who do not have their own nuclear weapons, using nuclear weapons supplied by the United States as part of a general NATO war plan, under the direction of NATO's Supreme Allied Commander. 

Protest in Amsterdam against the nuclear arms race between the U.S./NATO and the Soviet Union, 1981

 

Of the three nuclear powers in NATO (France, the United Kingdom, and the United States) only the United States has provided weapons for nuclear sharing. As of November 2009, Belgium, Germany, Italy, the Netherlands and Turkey are still hosting US nuclear weapons as part of NATO's nuclear sharing policy. Canada hosted weapons until 1984, and Greece until 2001. The United Kingdom also received US tactical nuclear weapons such as nuclear artillery and Lance missiles until 1992, despite the UK being a nuclear weapons state in its own right; these were mainly deployed in Germany.

In peacetime, the nuclear weapons stored in non-nuclear countries are guarded by US airmen though previously some artillery and missile systems were guarded by US Army soldiers; the codes required for detonating them are under American control. In case of war, the weapons are to be mounted on the participating countries' warplanes. The weapons are under custody and control of USAF Munitions Support Squadrons co-located on NATO main operating bases who work together with the host nation forces.

As of 2005, 180 tactical B61 nuclear bombs of the 480 US nuclear weapons believed to be deployed in Europe fall under the nuclear sharing arrangement. The weapons are stored within a vault in hardened aircraft shelters, using the USAF WS3 Weapon Storage and Security System. The delivery warplanes used are F-16s and Panavia Tornados.

Historical close calls

With the initiation of the Cold War arms race in the 1950s, an apocalyptic war between the United States and the Soviet Union became a real possibility. During the Cold War era (1947–1991), a number of military events have been described as having come quite close to potentially triggering World War III.

Korean War: 25 June 1950 – 27 July 1953

The Korean War was a war between two coalitions fighting for control over the Korean Peninsula: a communist coalition including North Korea, China and the USSR, and a capitalist coalition including South Korea, the United States, and the UN. Many then believed that the conflict was likely to soon escalate into a full-scale war between the three countries, the US, the USSR, and China. CBS war correspondent Bill Downs wrote in 1951 that, "To my mind, the answer is: Yes, Korea is the beginning of World War III. The brilliant landings at Inchon and the cooperative efforts of the American armed forces with the United Nations Allies have won us a victory in Korea. But this is only the first battle in a major international struggle which now is engulfing the Far East and the entire world." Downs afterwards repeated this belief on ABC Evening News while reporting on the USS Pueblo incident in 1968.

Cuban Missile Crisis: 15–28 October 1962

A US Navy HSS-1 Seabat helicopter hovers over Soviet submarine B-59, forced to the surface by US Naval forces in the Caribbean near Cuba. B-59 had a nuclear torpedo on board, and three officer keys were required to use it. Only one dissent prevented the submarine from attacking the US fleet nearby, a spark that could have led to a Third World War ( 28–29 October 1962).

 

The Cuban Missile Crisis: a confrontation on the stationing of Soviet nuclear missiles in Cuba, in response to the failed Bay of Pigs Invasion, is considered as having been the closest to a nuclear exchange, which could have precipitated a Third World War. The crisis peaked on 27 October, with three separate major incidents occurring on the same day, all of these incidents having been initiated by the US military.

• The "Arkhipov save" incident occurred when a Soviet submarine nearly launched a nuclear-tipped torpedo in response to having been targeted by American naval depth charges in international waters, with the Soviet nuclear launch response only having being prevented by Soviet naval officer Vasily Arkhipov.
• The shooting down of a U-2 while violating Cuban airspace.
• The near interception of another U-2 that had somehow managed to stray into Soviet airspace over Siberia, which airspace violation nearly caused the Soviets to believe that this might be the vanguard of a US aerial bombardment.

Despite what many believe to be the closest the world has come to a nuclear conflict, throughout the entire standoff, the Doomsday Clock, which is run by the Bulletin of the Atomic Scientists to estimate how close the end of the world, or doomsday, is, with midnight being the apocalypse, stayed at a relatively stable seven minutes to midnight. This has been explained as being due to the brevity of the crisis, since the clock monitored more long term factors such as leadership of countries, conflicts, wars, and political upheavals, as well as societies reactions to said factors. 

The Bulletin of the Atomic Scientists now credits the political developments resulting from the Cuban Missile Crisis with having actually enhanced global stability. The Bulletin posits that future crises and occasions that might otherwise escalate, were rendered as more stable due to two major factors:

1. A Washington to Moscow direct telephone line, resulted from the communication trouble between the White House and the Kremlin during the crisis, giving the leaders of the two largest nuclear powers the ability to contact each other in real time, rather than sending written messages that needed to be translated and wired, which had dragged out conversations in which seconds could have potentially prevented a nuclear exchange.
2. The second factor was caused in part due to the worldwide reaction to how close the US and USSR had come to the brink of World War III during the standoff. As the public began to more closely monitor topics involving nuclear weapons, and therefore to rally support for the cause of non-proliferation, the 1963 test ban treaty was signed. To date this treaty has been signed by 126 total nations, with the most notable exceptions being France and China. Both of these countries were still in the relative beginning stages of their nuclear programs at the time of the original treaty signing, and both sought nuclear capabilities independent of their allies.

-This Test Ban Treaty prevented the testing of nuclear ordnance that detonated in the atmosphere, limiting testing to below ground and under water, decreasing fallout and effects on the environment, and subsequently caused the Doomsday Clock to decrease by five minutes, to arrive at a total of twelve minutes to midnight. Up until this point, over 1000 nuclear bombs had been detonated, and concerns over both long and short term affects to the planet became increasingly more worrisome to scientists.

Yom Kippur War super-power tensions: 6–25 October 1973

The Yom Kippur War, also known as the Ramadan War, or October War, began with Arab victories. Israel successfully counterattacked. Tensions grew between the US (which supported Israel) and the Soviet Union (which sided with the Arab states). American and Soviet naval forces came close to firing upon each other. Admiral Murphy of the US reckoned the chances of the Soviet squadron attempting a first strike against his fleet at 40 percent. The Pentagon moved Defcon status from 4 to 3. The superpowers had been pushed to the brink of war, but tensions eased with the ceasefire brought in under UNSC 339.

NORAD computer error of 1979: 9 November 1979

The United States made emergency retaliation preparations after NORAD saw on-screen indications that a full-scale Soviet attack had been launched. No attempt was made to use the "red telephone" hotline to clarify the situation with the USSR and it was not until early-warning radar systems confirmed no such launch had taken place that NORAD realized that a computer system test had caused the display errors. A senator inside the NORAD facility at the time described an atmosphere of absolute panic. A GAO investigation led to the construction of an off-site test facility to prevent similar mistakes.

"Petrov save" incident: 26 September 1983

A false alarm occurred on the Soviet nuclear early warning system, showing the launch of American Minuteman ICBMs from bases in the United States. A retaliatory attack was prevented by Stanislav Petrov, an officer of the Soviet Air Defence Forces, who realised the system had simply malfunctioned (which was borne out by later investigations).

Able Archer escalations: 2–11 November 1983

During Able Archer 83, a ten-day NATO exercise simulating a period of conflict escalation that culminated in a DEFCON 1 nuclear strike, some members of the Soviet Politburo and armed forces treated the events as a ruse of war concealing a genuine first strike. In response, the military prepared for a coordinated counter-attack by readying nuclear forces and placing air units stationed in the Warsaw Pact states of East Germany and Poland under high alert. However, the state of Soviet preparation for retaliation ceased upon completion of the Able Archer exercises.

Norwegian rocket incident: 25 January 1995

The Norwegian rocket incident is the only World War III close call to occur outside the Cold War. This incident occurred when Russia's Olenegorsk early warning station accidentally mistook the radar signature from a Black Brant XII research rocket (being jointly launched by Norwegian and US scientists from Andøya Rocket Range), as appearing to be the radar signature of the launch of a Trident SLBM missile. In response, Russian President Boris Yeltsin was summoned and the Cheget nuclear briefcase was activated for the first and only time. However, the high command was soon able to determine that the rocket was not entering Russian airspace, and promptly aborted plans for combat readiness and retaliation. It was retrospectively determined that, while the rocket scientists had informed thirty states including Russia about the test launch, the information had not reached Russian radar technicians.

Incident at Pristina airport: 12 June 1999

On 12 June 1999, the day following the end of the Kosovo War, some 250 of Russian peacekeeping troops occupied the Pristina International Airport ahead of the arrival of NATO troops and were to secure the arrival of reinforcements over the air. American NATO Supreme Allied Commander Europe General Wesley Clark ordered the use of force against the Russians. Mike Jackson, British Army general who contacted the Russians during the incident, refused to enforce Clark's orders, famously telling him "I'm not going to start the Third World War for you." Captain James Blunt, the lead officer at the front of the Nato column in the direct armed stand-off against the Russians, received the "Destroy!" orders from Clark over the radio, but he followed Jackson's orders to encircle the airfield instead and later told in an interview that even without Jackson's intervention he would have refused to follow Clark's order. 

Extended usage of the term

Large nuclear weapons stockpile with global range (dark blue), smaller stockpile with global range (medium blue)

Cold War

As Soviet-American relations grew more tense in the post-World War II period, the fear that it could escalate into World War III was ever-present. A Gallup poll in December 1950 found that more than half of Americans considered World War III to have already started.

In 2004, commentator Norman Podhoretz proposed that the Cold War, lasting from the surrender of Japan and Germany until the fall of the Berlin Wall, might rightly be called World War III. By Podhoretz's reckoning, "World War IV" would be the global campaign against Islamofascism.

Still the majority of historians would seem to hold that World War III would necessarily have to be a worldwide "war in which large forces from many countries fought" and a war that "involves most of the principal nations of the world." In his book Secret Weapons of the Cold War, Bill Yenne explains that the military standoff that occurred between the two 'Superpowers', namely the United States and the Soviet Union, from the 1940s through to 1991, was only the Cold War, which ultimately helped to enable mankind to avert the possibility of an all out nuclear confrontation, and that it certainly was not World War III.

War on Terror

September 11 attacks

 

The "War on Terror" that began with the September 11 attacks has been claimed by some to be World War III or sometimes as World War IV. Others have disparaged such claims as "distorting American history." While there is general agreement amongst historians regarding the definitions and extent of the first two world wars, namely due to the unmistakable global scale of aggression and self-destruction of these two wars, a few have claimed that a "World War" might now no longer require such worldwide and large scale aggression and carnage. Still, such claims of a new "lower threshold of aggression," that might now be sufficient to qualify a war as a "World War" have not gained such widespread acceptance and support as the definitions of the first two world wars have received amongst historians.

War on ISIL

On 1 February 2015, Iraqi Foreign Minister Ibrahim al-Jaafari declared that the War on ISIL was effectively "World War III", due to ISIL's declaration of a Worldwide Caliphate, its aims to conquer the world, and its success in spreading the conflict to multiple countries outside of the Levant region. In response to the November 2015 Paris attacks, King of Jordan Abdullah II said "We are facing a Third World War [within Islam]."

In his State of the Union Address on 12 January 2016, U.S. President Barack Obama warned that news reports granting ISIL the supposed ability to foment WW III might be excessive and irresponsible, stating that, "as we focus on destroying ISIL, over-the-top claims that this is World War III just play into their hands. Masses of fighters on the back of pickup trucks and twisted souls plotting in apartments or garages pose an enormous danger to civilians and must be stopped. But they do not threaten our national existence."

Multiple small wars as a "third war"

In multiple recorded interviews under somewhat casual circumstances, comparing the conflagrations of World War I and II to the ongoing lower intensity wars of the 21st century, Pope Francis has said, "The world is at war, because it has lost peace," and "perhaps one can speak of a third war, one fought piecemeal."

Views on the likely outcome and definition

In 1949, after the unleashing of nuclear weaponry at the end of WWII, physicist Albert Einstein suggested that any outcome of a possible WWIII would be so dire as to revert mankind back to the Stone Age. When asked by journalist Alfred Werner, what types of weapons Einstein believed World War III might be fought with, Einstein warned, "I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones".

In his book Destined for War, Graham Allison views the global rivalry between the established power, the US, and the rising power, China, as an example of the Thucydides Trap. Past examples have often led to war, and in this case World War Three is possible but not inevitable.

Nuclear holocaust

From Wikipedia, the free encyclopedia

 

Mushroom cloud from the explosion of Castle Romeo in 1954.

 

A nuclear holocaust, nuclear apocalypse or atomic holocaust is a theoretical scenario involving widespread destruction and radioactive fallout causing the collapse of civilization, through the use of nuclear weapons. Under such a scenario, some or all of the Earth is made uninhabitable by nuclear warfare in future world wars. 

Besides the immediate destruction of cities by nuclear blasts, the potential aftermath of a nuclear war could involve firestorms, a nuclear winter, widespread radiation sickness from fallout, and/or the temporary loss of much modern technology due to electromagnetic pulses. Some scientists, such as Alan Robock, have speculated that a thermonuclear war could result in the end of modern civilization on Earth, in part due to a long-lasting nuclear winter. In one model, the average temperature of Earth following a full thermonuclear war falls for several years by 7 to 8 degrees Celsius on average.

Nonetheless, early Cold War-era studies suggested that billions of humans would survive the immediate effects of nuclear blasts and radiation following a global thermonuclear war. Some scholars argue that nuclear war could indirectly contribute to human extinction via secondary effects, including environmental consequences, societal breakdown, and economic collapse. Additionally, it has been argued that even a relatively small-scale nuclear exchange between India and Pakistan involving 100 Hiroshima yield (15 kilotons) weapons, could cause a nuclear winter and kill more than a billion people.

Since 1947, the Doomsday Clock of the Bulletin of the Atomic Scientists has visualized how close the world is to a nuclear war. 

The threat of a nuclear holocaust plays an important role in the popular perception of nuclear weapons. It features in the security concept of mutually assured destruction (MAD) and is a common scenario in survivalism. Nuclear holocaust is a common feature in literature and film, especially in speculative genres such as science fiction, dystopian and post-apocalyptic fiction.

Etymology and usage

The English word "holocaust", derived from the Greek term "holokaustos" meaning "completely burnt", refers to great destruction and loss of life, especially by fire.

One early use of the word "holocaust" to describe an imagined nuclear destruction appears in Reginald Glossop's 1926 novel The Orphan of Space: "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." In the novel, an atomic weapon is planted in the office of the Soviet dictator, who, with German help and Chinese mercenaries, is preparing the takeover of Western Europe.

References to nuclear destruction often speak of "atomic holocaust" or "nuclear holocaust.” For instance, U.S. President Bush stated in August 2007: "Iran's active pursuit of technology that could lead to nuclear weapons threatens to put a region already known for instability and violence under the shadow of a nuclear holocaust".

Likelihood of nuclear war

As of 2016, humanity has about 15,000 nuclear weapons, thousands of which are on hair-trigger alert. While stockpiles have been on the decline following the end of the Cold War, every nuclear country is currently undergoing modernization of its nuclear arsenal. Some experts believe this modernization may increase the risk of nuclear proliferation, nuclear terrorism, and accidental nuclear war.

John F. Kennedy estimated the probability of the Cuban Missile Crisis escalating to nuclear conflict as between 33% and 50%.

In a poll of experts at the Global Catastrophic Risk Conference in Oxford (17‐20 July 2008), the Future of Humanity Institute estimated the probability of complete human extinction by nuclear weapons at 1% within the century, the probability of 1 billion dead at 10% and the probability of 1 million dead at 30%. These results reflect the median opinions of a group of experts, rather than a probabilistic model; the actual values may be much lower or higher.

Scientists have argued that even a small-scale nuclear war between two countries could have devastating global consequences and such local conflicts are more likely than full-scale nuclear war.

Moral importance of human extinction risk

In his book Reasons and Persons, philosopher Derek Parfit posed the following question:

Compare three outcomes:

1. Peace.
2. A nuclear war that kills 99% of the world’s existing population.
3. A nuclear war that kills 100%.

(2) would be worse than (1), and (3) would be worse than (2). Which is the greater of these two differences?

He continues that "Most people believe that the greater difference is between (1) and (2). I believe that the difference between (2) and (3) is very much greater." Thus, he argues, even if it would be bad if massive numbers of humans died, human extinction would itself be much worse because it prevents the existence of all future generations. And given the magnitude of the calamity were the human race to become extinct, Nick Bostrom argues that there is an overwhelming moral imperative to reduce even small risks of human extinction.

Likelihood of complete human extinction

The United States and Soviet Union/Russia nuclear stockpiles, in total number of nuclear bombs/warheads in existence throughout the Cold War and post-Cold War era.

 

Many scholars have posited that a global thermonuclear war with Cold War-era stockpiles, or even with the current smaller stockpiles, may lead to human extinction. This position was bolstered when nuclear winter was first conceptualized and modelled in 1983. However, models from the past decade consider total extinction very unlikely, and suggest parts of the world would remain habitable. Technically the risk may not be zero, as the climactic effects of nuclear war are uncertain and could theoretically be larger than current models suggest, just as they could theoretically be smaller than current models suggest. There could also be indirect risks, such as a societal collapse following nuclear war that can make humanity much more vulnerable to other existential threats.

A related area of inquiry is: if a future nuclear arms race someday leads to larger stockpiles or more dangerous nuclear weapons than existed at the height of the Cold War, at what point could a war with such weapons result in human extinction? Physicist Leo Szilard warned in the 1950s that a deliberate "doomsday device" could be constructed by surrounding powerful hydrogen bombs with a massive amount of cobalt. Cobalt has a half-life of five years, and its global fallout might, some physicists have posited, be able to clear out all human life via lethal radiation intensity. The main motivation for building a cobalt bomb in this scenario is its reduced expense compared with the arsenals possessed by superpowers; such a doomsday device does not need to be launched before detonation, and thus does not require expensive missile delivery systems, and the hydrogen bombs do not need to be miniaturized for delivery via missile. The system for triggering it might have to be completely automated, in order for the deterrent to be effective. A modern twist might be to also lace the bombs with aerosols designed to exacerbate nuclear winter. A major caveat is that nuclear fallout transfer between the northern and southern hemispheres is expected to be small; unless a bomb detonates in each hemisphere, the effect of a bomb detonated in one hemisphere on the other is diminished.

Effects of nuclear war

Historically, it has been difficult to estimate the total number of deaths resulting from a global nuclear exchange because scientists are continually discovering new effects of nuclear weapons, and also revising existing models.

Early reports considered direct effects from nuclear blast and radiation and indirect effects from economic, social, and political disruption. In a 1979 report for the U.S. Senate, the Office of Technology Assessment estimated casualties under different scenarios. For a full-scale countervalue/counterforce nuclear exchange between the U.S. and the Soviet Union, they predicted U.S. deaths from 35 to 77 percent (70 million to 160 million dead at the time), and Soviet deaths from 20 to 40 percent of the population.

Although this report was made when nuclear stockpiles were at much higher levels than they are today, it also was made before the risk of nuclear winter was first theorized in the early 1980s. Additionally, it did not consider other secondary effects, such electromagnetic pulses (EMP), and the ramifications they would have on modern technology and industry.

Nuclear winter

In the early 1980s, scientists began to consider the effects of smoke and soot arising from burning wood, plastics, and petroleum fuels in nuclear-devastated cities. It was speculated that the intense heat would carry these particulates to extremely high altitudes where they could drift for weeks and block out all but a fraction of the sun's light. A landmark 1983 study by the so-called TTAPS team (Richard P. Turco, Owen Toon, Thomas P. Ackerman, James B. Pollack and Carl Sagan) was the first to model these effects and coined the term "nuclear winter."

More recent studies make use of modern global circulation models and far greater computer power than was available for the 1980s studies. A 2007 study examined consequences of a global nuclear war involving moderate to large portions of the current global arsenal. The study found cooling by about 12–20 °C in much of the core farming regions of the US, Europe, Russia and China and as much as 35 °C in parts of Russia for the first two summer growing seasons. The changes they found were also much longer lasting than previously thought, because their new model better represented entry of soot aerosols in the upper stratosphere, where precipitation does not occur, and therefore clearance was on the order of 10 years. In addition, they found that global cooling caused a weakening of the global hydrological cycle, reducing global precipitation by about 45%. 

The authors did not discuss the implications for agriculture in depth, but noted that a 1986 study which assumed no food production for a year projected that "most of the people on the planet would run out of food and starve to death by then" and commented that their own results show that, "This period of no food production needs to be extended by many years, making the impacts of nuclear winter even worse than previously thought."

In contrast to the above investigations of global nuclear conflicts, studies have shown that even small-scale, regional nuclear conflicts could disrupt the global climate for a decade or more. In a regional nuclear conflict scenario where two opposing nations in the subtropics would each use 50 Hiroshima-sized nuclear weapons (about 15 kiloton each) on major populated centres, the researchers estimated as much as five million tons of soot would be released, which would produce a cooling of several degrees over large areas of North America and Eurasia, including most of the grain-growing regions. The cooling would last for years, and according to the research, could be "catastrophic". Additionally, the analysis showed a 10% drop in average global precipitation, with the largest losses in the low latitudes due to failure of the monsoons.

Regional nuclear conflicts could also inflict significant damage to the ozone layer. A 2008 study found that a regional nuclear weapons exchange could create a near-global ozone hole, triggering human health problems and impacting agriculture for at least a decade. This effect on the ozone would result from heat absorption by soot in the upper stratosphere, which would modify wind currents and draw in ozone-destroying nitrogen oxides. These high temperatures and nitrogen oxides would reduce ozone to the same dangerous levels we now experience below the ozone hole above Antarctica every spring.

Nuclear famine

It is difficult to estimate the number of casualties that would result from nuclear winter, but it is likely that the primary effect would be global famine (known as Nuclear Famine), wherein mass starvation occurs due to disrupted agricultural production and distribution. In a 2013 report, the International Physicians for the Prevention of Nuclear War (IPPNW) concluded that more than two billion people, about a third of the world's population, would be at risk of starvation in the event of a regional nuclear exchange between India and Pakistan, or by the use of even a small proportion of nuclear arms held by the U.S. and Russia. Several independent studies show corroborated conclusions that agricultural outputs will be significantly reduced for years by climatic changes driven by nuclear wars. Reduction of food supply will be further exacerbated by rising food prices, affecting hundreds of millions of vulnerable people, especially in the poorest nations of the world.

Electromagnetic pulse

An electromagnetic pulse (EMP) is a burst of electromagnetic radiation. Nuclear explosions create a pulse of electromagnetic radiation called a nuclear EMP or NEMP. Such EMP interference is known to be generally disruptive or damaging to electronic equipment. If a single nuclear weapon "designed to emit EMP were detonated 250 to 300 miles up over the middle of the country it would disable the electronics in the entire United States."

Given that many of the comforts and necessities we enjoy in the 21st century are predicated on electronics and their functioning, an EMP would disable hospitals, water treatment facilities, food storage facilities, and all electronic forms of communication. An EMP blast threatens the foundation which supports the existence of the modern human condition. Certain EMP attacks could lead to large loss of power for months or years. Currently, failures of the power grid are dealt with using support from the outside. In the event of an EMP attack, such support would not exist and all damaged components, devices, and electronics would need to be completely replaced.

In 2013, the US House of Representatives considered the "Secure High-voltage Infrastructure for Electricity from Lethal Damage Act" that would provide surge protection for some 300 large transformers around the country. The problem of protecting civilian infrastructure from electromagnetic pulse has also been intensively studied throughout the European Union, and in particular by the United Kingdom. While precautions have been taken, James Woolsey and the EMP Commission suggested that an EMP is the most significant threat to the U.S. The greatest threat to human survival in the aftermath of an EMP blast would be the inability to access clean drinking water. For comparison, in the aftermath of the 2010 Haitian earthquake, the water infrastructure had been devastated and led to at least 3,333 deaths from cholera in the first few months after the earthquake. Other countries would similarly see the resurgence of previously non-existent diseases as clean water becomes increasingly scarce.

The risk of an EMP, either through solar or atmospheric activity or enemy attack, while not dismissed, was suggested to be overblown by the news media in a commentary in Physics Today. Instead, the weapons from rogue states were still too small and uncoordinated to cause a massive EMP, underground infrastructure is sufficiently protected, and there will be enough warning time from continuous solar observatories like SOHO to protect surface transformers should a devastating solar storm be detected.

Nuclear fallout

Nuclear fallout is the residual radioactive dust and ash propelled into the upper atmosphere following a nuclear explosion. Fallout is usually limited to the immediate area, and can only spread for hundreds of miles from the explosion site if the explosion is high enough in the atmosphere. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain (rain darkened by soot and other particulates). 

This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron activated by exposure, is a highly dangerous kind of radioactive contamination. The main radiation hazard from fallout is due to short-lived radionuclides external to the body. While most of the particles carried by nuclear fallout decay rapidly, some radioactive particles will have half-lives of seconds to a few months. Some radioactive isotopes, like strontium 90 and cesium 137, are very long lived and will create radioactive hot spots for up to 5 years after the initial explosion. Fallout and black rain may contaminate waterways, agriculture, and soil. Contact with radioactive materials can lead to radiation poisoning through external exposure or accidental consumption. In acute doses over a short amount of time radiation will lead to prodromal syndrome, bone marrow death, central nervous system death and gastrointestinal death. Over longer periods of exposure to radiation, cancer becomes the main health risk. Long term radiation exposure can also lead to in utero effects on human development and transgenerational genetic damage.

Origins and analysis of extinction hypotheses

As a result of the extensive nuclear fallout of the 1954 Castle Bravo nuclear detonation, author Nevil Shute wrote the popular novel On the Beach which was released in 1957, in this novel so much fallout is generated in a nuclear war that all human life is extinguished. However the premise that all of humanity would die following a nuclear war and only the "cockroaches would survive" is critically dealt with in the 1988 book Would the Insects Inherit the Earth and Other Subjects of Concern to Those Who Worry About Nuclear War by nuclear weapons expert Philip J. Dolan.

In 1982 nuclear disarmament activist Jonathan Schell published The Fate of the Earth, which is regarded by many to be the first carefully argued presentation that concluded that extinction is a significant possibility from nuclear war. However, the assumptions made in this book have been thoroughly analyzed and determined to be "quite dubious". The impetus for Schell's work, according to physicist Brian Martin, was to argue that "if the thought of 500 million people dying in a nuclear war is not enough to stimulate action, then the thought of extinction will. Indeed, Schell explicitly advocates use of the fear of extinction as the basis for inspiring the "complete rearrangement of world politics".

The belief in "overkill" is also commonly encountered, with an example being the following statement made by nuclear disarmament activist Philip Noel-Baker in 1971 – "Both the US and the Soviet Union now possess nuclear stockpiles large enough to exterminate mankind three or four – some say ten – times over". Brian Martin suggested that the origin of this belief was from "crude linear extrapolations", and when analyzed it has no basis in reality. Similarly, it is common to see stated that the combined explosive energy released in the entirety of World War II was about 3 megatons, while a nuclear war with warhead stockpiles at Cold War highs would release 6000 WWII's of explosive energy. An estimate for the necessary amount of fallout to begin to have the potential of causing human extinction is regarded by physicist and disarmament activist Joseph Rotblat to be 10 to 100 times the megatonnage in nuclear arsenals as they stood in 1976; however, with the world megatonnage decreasing since the Cold War ended this possibility remains hypothetical.

According to the 1980 United Nations report General and Complete Disarmament: Comprehensive Study on Nuclear Weapons: Report of the Secretary-General, it was estimated that there were a total of about 40,000 nuclear warheads in existence at that time, with a potential combined explosive yield of approximately 13,000 megatons. 

By comparison, in the Timeline of volcanism on Earth when the volcano Mount Tambora erupted in 1815 – turning 1816 into the Year Without A Summer due to the levels of global dimming sulfate aerosols and ash expelled – it exploded with a force of roughly 800 to 1,000 megatons, and ejected 160 km³ (38 cu mi) of mostly rock/tephra, which included 120 million tonnes of sulfur dioxide as an upper estimate. A larger eruption, approximately 74,000 years ago, in Mount Toba produced 2,800 km³ (670 cu mi) of tephra, forming lake Toba, and produced an estimated 6,000 million tonnes (6.6×10⁹ short tons) of sulfur dioxide. The explosive energy of the eruption may have been as high as equivalent to 20,000,000 megatons (Mt) of TNT, while the Chicxulub impact, connected with the extinction of the dinosaurs, corresponds to at least 70,000,000 Mt of energy, which is roughly 7000 times the maximum arsenal of the US and Soviet Union.

However, it must be noted that comparisons with supervolcanos are more misleading than helpful due to the different aerosols released, the likely air burst fuzing height of nuclear weapons and the globally scattered location of these potential nuclear detonations all being in contrast to the singular and subterranean nature of a supervolcanic eruption. Moreover, assuming the entire world stockpile of weapons were grouped together, it would be difficult due to the nuclear fratricide effect to ensure the individual weapons would detonate all at once. Nonetheless, many people believe that a full-scale nuclear war would result, through the nuclear winter effect, in the extinction of the human species, though not all analysts agree on the assumptions inputted into these nuclear winter models.