"The prospect of nuclear conflict, once unthinkable, is now back within the realm of possibility."

This is the judgment of Antonio Guterres, Secretary-General of the United NationsAn international organisation focused on keeping peace. Its refugee agency, the UNHCR, aims to assist refugees around the world.: Russia's invasion of Ukraine has brought the world closer to nuclear catastrophe than we have been since the Cold WarA period of diplomatic conflict between blocs led by the USA and the USSR that lasted from 1947 until 1991, when the USSR collapsed..

Russia has fired a hypersonicTravelling at speeds of more than five times the speed of sound (Mach 5). ballistic missile. Known as the Kinzhal, or Dagger, the weapon can hit a target up to 1,240 miles away and can fly up to 6,000mph. It is also capable of carrying nuclear warheadsThe device containing nuclear materials, fitted onto a missile, torpedo or bomb..

Observers point out the attack proves Putin's willingness to use nuclear capabilities. "It's a signal to the West", says Dominika Kunertova of the Center for Security Studies in Zurich.

Russia has more nuclear weaponsA bomb or other weapon that uses nuclear energy to cause a big explosion. than any other country: an estimated 5,977 warheads, many of which have the ability to destroy cities.

If Russia and the USA unleashed the full potential of their arsenals, hundreds of thousands could be killed in a day. This could be followed by radiation, firestorms and a "nuclear winter".

Is Putin ready to go down this apocalyptic route? Most experts think not. "His objective is not to bring the world to nuclear war," says Paul Hare, an academic and former diplomat.

This does not mean he would not use nuclear weapons. According to intelligence reports, Russia is prepared to respond to perceived threatsRussia watchers say that Putin believes that the USA and European powers are seeking to remove him from power and that he interprets economic sanctions as preparations for war. by firing a smaller weapon into foreign territory as a warning: a so-called "tactical" nuclear strike. The more cornered Putin feels, the more likely he is to resort to this option.

Even a smaller strike that didn't target a populated area would have terrible consequences. It would cause severe damage and break the "nuclear taboo" that has held world leaders back since 1946The year when the USA dropped atom bombs on the Japanese cities of Hiroshima and Nagasaki, killing an estimated 200,000 people. This is the only use of nuclear weapons to date..

If Russia were to use a single nuclear bomb as a deterrentSomething that prevents people from doing something by making them afraid of what will happen to them if they do it., it is unclear whether the USA and its allies would respond. The US Defense Department has role-played this scenario. One ended in retaliation, the other did not. 

How likely is this? Most experts think the possibility is not unthinkable. "The chance for nuclear weapons employment is extremely low," says Ulrich Kuhn of Hamburg University. "But it's not zero. It's real, and it might even increase."

Yes: Putin clearly has no concern for human life. Now he is isolated, humiliated and embattled. For such a man in such a situation, the nuclear button must be difficult to resist.

No: Putin is rash and aggressive, but not insane: he is not prepared to sacrifice Russia or himself. For all his posturing, he knows that there can be no victors in a nuclear war.

Or... The main threat is not the temperament of one individual but the fact that nuclear weapons exist at all. As long as these agents of apocalypse befoul our planet, we are only a misstep away from annihilation. We must disarm at all costs.