Human civilisation had a good run — for about 6,500 years, actually — and now we will perish in fire, famine, drought, never-ending winters, disease and chaos. A single megaton nuclear weapon dropped on the House of Commons would kill more than a million people outright. Nearly 2.5 million would be burned, maimed and injured. The fireball radius — the area that represents total annihilation — would stretch for nearly a kilometre.

That’s just one bomb, of course. What if 100 nuclear warheads with a much lower yield — 15 kilotons, say, the size of the bomb dropped on Hiroshima — were exchanged on the Indian subcontinent? Well, scientists have modelled this scenario, and the calamity extends far beyond the borders of India and Pakistan. As five megatons of black carbon instantly enter the atmosphere, temperatures will suddenly fall, rainfall will decline, the ozone layer will thin dramatically and the frost-free growing period for crops will shorten by between 10 and 40 days. According to the International Physicians for the Prevention of Nuclear War, 2 billion people could starve in the aftermath. In a full East-West exchange billions would also die. Infrastructure would collapse. The survivors would, it is often said, envy the dead. They would suffer torturous protracted deaths from radiation; they would scrabble for food in irradiated soil; as health-care systems implode, their illnesses and cancers would be untreated. For the diminishing minority who remained alive, it would be everyone for themselves in a struggle for survival in a ravaged hellscape.

Why inflict this horror on your imagination? It seems so abstract and distant, and yet, according to the Doomsday Clock of the Bulletin of the Atomic Scientists, so near. The US and Russia combined have around 2,000 nuclear weapons on a hair trigger, meaning they could be launched in minutes, leaving my scenarios just hours away.

There have been many close calls. In 1979, Zbigniew Brzezinski — former US president Jimmy Carter’s national security adviser — was woken up at 3am to be told that 250 Soviet nuclear missiles were heading to the US. If the president were to retaliate, he would have between three and seven minutes to decide. An updated report came through: There were 2,200 missiles. Armageddon beckoned. But the reports were wrong. “Someone had mistakenly put military exercise tapes into the computer system,” as the former defence secretary Robert Gates put it. Consider today, with US President Donald Trump in the White House facing off against North Korea’s Kim Jong-un. A nuclear arsenal on a hair trigger under the control of a man whose Twitter feed is a never-ending temper tantrum is not exactly reassuring. Millions could perish in a nuclear conflagration in a matter of hours.

Which brings me to the noble but marginalised cause of nuclear disarmament. Tomorrow marks 60 years since the first march to Aldermaston — where Britain’s nuclear bombs are produced — which spawned the Campaign for Nuclear Disarmament (CND).

Listen to former United Kingdom prime minister Tony Blair’s defence secretary Des Browne, who suggested that cyber attacks against Trident could render it obsolete. Blair himself said he could see “the common sense and practical argument” against Trident, that “the expense is huge, and the utility in a post-cold war world is less in terms of deterrent, and nonexistent in terms of military use”. We fail to adequately tackle the actual threats facing Britain, for instance, and leave our conventional forces under-resourced because of the Trident obsession. Nearly a decade ago, Field Marshall Lord Bramall — former head of the armed forces — and two senior generals described nukes as “completely useless as a deterrent to the threats and scale of violence we currently face or are likely to face”. Take terrorism, take cyber-attacks, take climate change: All pose grave, demonstrable threats to our security. Yet, we are failing to invest in tackling them, while billions are thrown at weapons of mass destruction that do not keep us safe. There are many steps that can be taken like running a campaign that asks Russia and the US to cease putting their arsenal on hair-trigger alert. We should exert moral pressure on nations to sign up to the comprehensive test ban treaty. Britain cannot disarm the world, but it can set an example. The nightmare of nuclear apocalypse hangs over humanity. It will one day become a reality, unless we stop it.

— Guardian News & Media Ltd

Owen Jones is an English columnist, author, commentator and political activist.