With arms control agreements collapsing and arsenals expanding, the risk of nuclear war – deliberate or accidental – is rising in a fragile global environment.

It is widely thought that the 5 February expiration of New START – the last arms control agreement capping US and Russian nuclear weapons – could usher in a dangerous and highly destabilising new nuclear arms race. Since the Cold War peak of over 70,000 nuclear weapons in 1986, arms control treaties have reduced the number to approximately 12,200 today – still equivalent, however, to 145,000 Hiroshimas. Many of these decommissioned weapons remain in storage where they can be readily redeployed, making it possible to double Russian and US arsenals in one to two years.

If a new nuclear arms race begins between the US and Russia, the US could “upload” 800 bombs and cruise missiles stored at military bases back onto B-2 and B-52 bombers in a matter of weeks. The number of warheads on submarines could be increased by 400 to 500 by placing additional warheads on each missile and reusing the launch tubes that were closed under New START. Finally, by placing additional warheads on half of its ICBMs and reloading silos on standby, it could double its ICBM warheads from 400 to 800. Similarly, hundreds of decommissioned Russian warheads could be uploaded onto its bombers, ICBMs and submarines.

Moreover, both the US and Russia are modernising their nuclear weapons and new, terrifying systems are being developed. Although their arsenals are much smaller, the other seven nuclear weapon states are also modernising, and China is rapidly expanding its arsenal. France has also just announced it will also increase the size of its arsenal. Several non-nuclear states are considering acquiring nuclear weapons, which would further proliferation and greatly complicate the global situation.

The development of nuclear weapons in space and dual-use technology add to the unpredictability and the loss of verification and information-exchange provided by arms control agreements contribute to greater uncertainty, misunderstanding and worst-case thinking.

So, will a new nuclear arms race make us more secure?

Given the current very tense and fragile geopolitical environment and questions about the stability of the leaders involved, it is entirely possible that a conventional conflict could escalate into nuclear war. Indeed, the Russians have threatened to use nuclear weapons in the context of their war in Ukraine and they have also lowered their “nuclear doctrine” threshold for using nuclear weapons.

The book _Nuclear War: A Scenario_ and the film _A House of Dynamite_ both offer chilling but realistic scenarios whereby incoming ICBMs would be responded to by massive second-strike retaliation. In just over an hour, life as we know it would be shattered worldwide.

The other grave concern is accidental nuclear war; published accounts offer multiple examples. Warnings of a nuclear attack have been triggered by a faulty 46-cent computer chip; the mistaken insertion of a training tape into a computer; moon-rise; nuclear submarine collisions; the launch of a weather rocket; and many others.

There are also cyberthreats that barely existed during the Cold War. Equally worrying is the slippery slope of AI which could lead to its integration into US, Russian and Chinese nuclear weapon systems, stimulated by competition, mutual insecurity and the extremely short decision-making time-frame.

As Gareth Evans, Co-chair of the International Commission on Nuclear Non-proliferation and Disarmament, warns: “The fact that we have survived for eight decades without a nuclear weapons catastrophe . . . is just sheer, dumb luck.”

A nuclear war would be utterly catastrophic. Scientific evidence has shown that a nuclear war would cause a “nuclear winter” where smoke and soot from hundreds of burning cities would loft into the upper atmosphere, blocking sunlight, darkening the sky, chilling the Earth, creating massive crop failures and extreme famine for every country in the world for up to 10 years after an all-out nuclear war. Millions of deaths from the explosions and radiation would be followed by billions of deaths from starvation.

It would also significantly deplete the ozone layer, threatening animal and plant life. Recently, it has been shown that even a “limited” war between India and Pakistan could cause a nuclear winter that could kill over two billion people.

As Jonathan Schell writes in _The Fate of the Earth_: “The machinery of destruction is complete, poised on a hair trigger, waiting for the ‘button’ to be ‘pushed’ by some misguided or deranged human being or for some faulty computer ship to send out the instructions to fire. That so much should be balanced on so fine a point – that the fruit of four and a half billion years can be undone in a careless moment – is a fact against which belief rebels.”

Indeed, in January, the Doomsday Clock set annually by The Bulletin of the Atomic Scientists was moved to its closest point to midnight in its history – 85 seconds. The Bulletin’s president/CEO, Alexandra Bell, said: “The Doomsday Clock’s message cannot be clearer. Catastrophic risks are on the rise, cooperation is on the decline, and we are running out of time. Change is both necessary and possible, but the global community must demand swift action from their leaders.”

Unfortunately, little remains of the broad-based anti-nuclear activism that was prevalent during the Cold War. Nevertheless, there is considerable public concern. A YouGov poll from May 2025 conducted in the US and five European countries shows that 41 to 55 per cent of respondents think another world war is likely within the next five to 10 years and 68 to 76 per cent believe that, if one occurs, it would involve nuclear weapons. Furthermore, 25 to 44 per cent believe that it would result in the deaths of most of the world’s population.

If those who are worried about nuclear war were to become involved in a vigorous public debate to educate and activate those who aren’t aware of the magnitude of the threat (including those in power) to urge leaders to re-engage in significant, new arms control negotiations and agreements, they could surely make a difference, as they did during the Cold War, for this most existential of all threats.

As Schell notes: “Every person is the right person to act. Every minute is the right moment to begin.”