The use of nuclear weapons is objectively more likely than it has been for years – perhaps since the 1962 Cuban Missile Crisis. Yet we appear curiously unconcerned. It seems we can hold only one apocalyptic scenario in our heads at any given time. When I was growing up, it was a nuclear exchange. Now it is global warming.

Cast your mind back to the Seventies and Eighties. The mushroom cloud was a familiar icon in popular culture, seen on book covers, record sleeves and film posters. Think of the Terminator, Mad Max or Planet of the Apes series, of On the Beach, Threads or When the Wind Blows. I can remember TV adverts telling us how to take cover in the event of a nuclear strike. We even had a shelter at my prep school.

All that now seems frightfully vieux chapeau. Hollywood has moved on to climate change – Waterworld, Snowpiercer, The Day After Tomorrow. Audiences don’t like to be confused by having the older peril dredged up.

Yet the threat of nuclear obliteration has not gone away. The number of nuclear states has grown from five to nine, with Iran hammering at the door. Now the nation with the second-largest arsenal is led by a man who might have nothing to lose.

Before we come to Vladimir Putin, though, let’s consider why we have become so blasé. Part of the answer, obviously, is that the Cold War ended in 1990. But a bigger factor, it seems to me, is that a taboo has grown up around a first strike, a taboo strengthened by each year of non-use. In the fifties, nuclear missiles were seen as one among many weapons – more destructive, to be sure, but not in a different ethical category.

As time passed, though, the idea of unleashing decades of sickness and genetic deformity on an entire population started to become unthinkable. Richard Nixon did not nuke Hanoi in 1972; Margaret Thatcher did not nuke Buenos Aires in 1982; Putin, come to that, did not nuke Lviv in 2014. Twelve countries, including Brazil, Taiwan and South Africa, actually chose to discontinue their nuclear weapons programmes.

With each passing year, nuclear weapons came to be seen, not just as horrifying, but as evil. People began to use Biblical language to describe their use: Armageddon, Holocaust, Apocalypse. Churchmen saw banning the bomb as a moral cause.

It is worth remembering that this wasn’t always the case. At the first Aldermaston march in 1958, the then Archbishop of Canterbury, Geoffrey Fisher, refused to endorse CND on grounds that everyone was eventually going to be swept from this world to the next, and that it was not his job as a clergyman to fret about the timing of the transition.

“There is no evidence that the human race is to last forever, and plenty in Scripture to the contrary effect,” declared the prelate stoutly. “Christ in His Crucifixion showed us how to suffer creatively. He did not claim to end suffering, nor did He bid His disciples to avoid suffering. So I repeat, I cannot establish any policy merely on whether or not it will save the human race from a period of suffering or from extinction. For all I know, it is within the providence of God that the human race should destroy itself in this manner.”

His reasoning, though theologically defensible, nowadays strikes us as shocking. Our shock has grown precisely because the threat has receded – or, rather, been displaced.

Seventy-five years ago, the Bulletin of Atomic Scientists launched the famous Doomsday Clock, purportedly showing how close we were to nuclear extinction. In 1947, the hands were set at seven minutes to midnight. Now, we are said to have just 100 seconds left. This is not because a nuclear war is deemed more likely but because, in 2007, the function of the clock was redefined. As the editor, John Mecklin, puts it: “Climate change, biological threats, artificial intelligence – there are lots of emerging issues that could threaten the planet.”

Distracted by these novel dangers, we lost interest in the original one. Little wonder, then, that we were so shaken when, on the first day of the invasion, Putin threatened the West with “consequences greater than any you have faced in history.”

Since then, almost everything has gone wrong for the unsmiling dictator. The budget he had set aside from 2014 to grease the palms of key Ukrainian officials – mayors, governors, generals, police chiefs – so that they would swap sides when the moment came, was embezzled by his spy chiefs, leading to the arrest of the entire leadership of the FSB’s Fifth Service last month. The money that was meant to have gone on modernising Russia’s army also disappeared into numbered Cyprus accounts, leaving tanks stranded for want of spare parts.

Now the most powerful vessel in Russia’s Black Sea Fleet, the Moskva, has been sunk, reportedly going down (aptly enough at this paschal season) with a fragment of the True Cross.

It is hard not to think of Russia’s defeat at the hands of the Japanese in 1905, when their Baltic Fleet spent seven months steaming to the Pacific to be destroyed in seven hours. Putin knows that the Tsar’s regime never recovered. An autocrat can survive many things. But he cannot survive military disaster.

Could Putin, who is said to be behaving erratically, and whose very launch of this war flew in the face of all reason, be tempted to escalate? Russia has battlefield nuclear weapons whose blast, if not as destructive as Hiroshima, is comparable to the 2020 Beirut explosion which left 300,000 people homeless. Might the Kremlin conclude that, if defeat is coming, it is politically less disastrous to lose to Nato than to lose to Ukraine?

Perhaps. But think of the risks from Putin’s point of view. First, there is a possibility that his attempt to escalate would prompt a Kremlin putsch from those generals who don’t want their country to carry the mark of Cain for decades.

Then, there is a chance that his nuclear weapons will prove as shoddy and ineffective as his conventional arms, possibly even detonating in the wrong place. He cannot know whether Western anti-missile defence shields might shoot his rockets down. And even if they worked – even if he managed to flatten Lviv – what then? Putin would be excoriated for the rest of human history as a monster, and for what? What would Russia have won?

All this is true. But if the likelihood of nuclear missiles being launched on this occasion is tiny, it is not zero. As long as the weapons exist, they might be used. Perhaps Putin is more ill or more deranged than we imagine. Perhaps there will be an accident – Boris Yeltsin came close to retaliating against what turned out to be a Norwegian scientific rocket in 1995. Perhaps the ayatollahs in Tehran will see the loosening of sanctions as an opportunity to fulfil their morbid ambitions. Or perhaps some terrorist group will get its hands on plutonium or enriched uranium, pack it around a detonator and leave it in a city centre.

Suppose that, on any given day, there is a one in a million chance of a strike, whether accidental or deliberate. That might sound reassuringly unlikely but, given enough time, those odds make a nuclear explosion certain. Anton Chekhov once wrote that a gun which makes its appearance on stage in Act One will be fired before the end of Act Three. The gun, in this case, has been on stage since 1945.

What, then, can we do about it? Ideally, we would agree to eliminate all nuclear weapons. That might prove impractical, though. What if some weapons were secretly retained or sold? What if there were a new rush to become the world’s sole nuclear power?

If abolition is impossible, the next best option is a space-based defensive shield that could be extended to every country – including Russia. Ronald Reagan began such a programme in 1984, Bill Clinton discontinued it in 1993 and Donald Trump revived it in 2019. It may even be possible, if Ukraine wins this war, to impose a measure of denuclearisation on a defeated Russia.

In any event, let us keep our sense of perspective. The planetary calamity that was widely seen as inevitable in the 1950s has, so far, failed to materialise. As the sensible Archbishop Fisher put it, “Man shall not live by dread alone.”