The UK would "cease to exist" if a nuclear World War Three began and even the safest locations would suffer from a "nuclear winter", experts state.
Professor Andrew Futter, from the University of Leicester, said that the Russian president Vladamir Putin does not have much to gain from resorting to nuclear weapons but warned that a civil war may leave him desperate.
The specialist in international politics added that Russia using nuclear weapons remains a long way off. However, Professor Futter and a number of other leading experts have revealed what the world would look like if WW3 really did break out.
Professor Campbell Craig, of Cardiff University, states that hoping the USA would destroy Russian missiles in time is "optimistic" and that most Western cities would be powerless against being reduced to ruin, The Daily Star writes.
He said: "If a nuclear war broke out between NATO and Russia and escalated to a general war, most cities in Russia, Europe, and the US would be targeted and destroyed. The UK would basically cease to exist.
"Things can go wrong and the US might be able to intercept some missiles or destroy some of the Russian arsenal before it is launched, but that's optimistic."
His bleak outlook is echoed by Harvard Kennedy School's Professor Matthew Bunn who said even those in the most remote corners of the Earth could be impacted by nuclear warfare.
Prof Bunn whose research centres around nuclear arms and technology, said that "the capitals and major cities of the major nuclear-armed states" would be the first to go.
He continued: "But the effects could affect everyone – not only because our societies are so interconnected (as COVID has shown us) but because the smoke from burning cities could rise into the upper atmosphere, darken the sun, and create a 'nuclear winter' that could interfere with agriculture globally."
What makes the threat of nuclear weapons especially terrifying is how much technology has evolved since the "relatively small" explosions in Hiroshima and Nagasaki in Japan after World War Two.
Prof Futter agrees that the impact of a nuclear blast let alone several would reach far beyond the cities blown to pieces.
He said: "Even a small use of nuclear weapons would have significant global consequences. Two relatively small nuclear bombs killed approximately 200,000 people in Hiroshima and Nagasaki in 1945.
"Today’s nuclear weapons are much more powerful and Russia has several thousand nuclear weapons that can be used.
"It is not just the destruction and death caused by a nuclear blast, the fireball and over-pressure that it produces but the enormous amounts of radiation and fallout that would be produced that would likely impact the whole of Europe."
Compared to when Russia US hostility hit a fever pitch during the Cold War, Professor Craig explained a new player has emerged and now China would feature heavily in a projected map of WW3.
In response to a map illustrating the potential consequences of the Cuban missile crisis, he said: "Not really a whole lot different now, though things would change were China to get involved (it was not a nuclear power in 1962). Also back then the Soviet Union relied mainly on bombers rather than missiles so it's possible that damage to the US and maybe Western Europe wouldn't have been as bad."
For the time being, Prof Futter expects China and North Korea to stay out of the Ukraine crisis but admits the war might be used as a smokescreen for North Korea to continue developing or even testing its own capabilities.
Realistically the threat of nuclear war currently remains low particularly as radiation and fallout would very likely impact Russian and Belarusian towns and cities close to the Ukrainian border, according to Prof Futter.
He explained that Putin's bold announcement was probably designed to deter any Western/NATO direct military interference in the conflict, such as establishing a no-fly zone or sending troops.
"However, if President Putin finds himself bogged down in Ukraine, losing more troops and fighting what could become a bloody civil war, he may become desperate, Prof Futter warned.
"In this scenario it is not impossible that he might consider exploding a small nuclear device high in the air (i.e. not designed to kill to destroy) as a warning shot to NATO/the West to stop their support to Ukraine."
Prof Futter added: "The would be a massive gamble, and would be the first time a nuclear weapon has been exploded in wartime since 1945.
"It is unlikely that President Putin would use nuclear weapons in Ukraine - It is also difficult to see what military objective this would achieve given that the future of the conflict is likely to be close-combat if not guerrilla warfare."
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