The consequences of nuclear war would be devastating. Much more should—and can—be done to reduce the risk that humanity will ever fight such a war.

The shockwave and heat that the detonation of a single nuclear weapon creates can end the lives of millions of people immediately. 

But even larger is the devastation that would follow a nuclear war. 

The first reason for this is nuclear fallout. Radioactive dust from the detonating bombs rises up into the atmosphere and spreads out over large areas of the world from where it falls down and causes deadly levels of radiation.

The second reason is less widely known. But this consequence – ‘nuclear winter’ and the worldwide famine that would follow – is now believed to be the most serious consequence of nuclear war.

Cities that are attacked by nuclear missiles burn at such an intensity that they create their own wind system, a firestorm: hot air above the burning city ascends and is replaced by air that rushes in from all directions. The storm-force winds fan the flames and create immense heat. 

From this firestorm large columns of smoke and soot rise up above the burning cities and travel all the way up to the stratosphere. There it spreads around the planet and blocks the sun’s light. At that great height – far above the clouds – it cannot be rained out, meaning that it will remain there for years, darkening the sky and thereby drying and chilling the planet.

The nuclear winter that would follow a large-scale nuclear war is expected to lead to temperature declines of 20 or even 30 degrees Celsius (60–86° F) in many of the world’s agricultural regions – including much of Eurasia and North America. Nuclear winter would cause a ‘nuclear famine’. The world’s food production would fail and billions of people would starve.¹

These consequences – nuclear fallout and nuclear winter leading to famine – mean that the destruction caused by nuclear weapons is not contained to the battlefield. It would not just harm the attacked country. Nuclear war would devastate all countries, including the attacker. 

The possibility of global devastation is what makes the prospect of nuclear war so very terrifying. And it is also why nuclear weapons are so unattractive for warfare. A weapon that can lead to self-destruction is not a weapon that can be used strategically. 

US President Reagan put it in clear words at the height of the Cold War: “A nuclear war cannot be won and must never be fought. The only value in our two nations possessing nuclear weapons is to make sure they will never be used. But then would it not be better to do away with them entirely?”²

But the chart also shows that there are still almost ten thousand nuclear weapons distributed among nine countries on our planet, at least.³ Each of these weapons can cause enormous destruction; many are much larger than the ones that the US dropped on Hiroshima and Nagasaki.⁴ 

Collectively these weapons are immensely destructive. The nuclear winter scenario outlined above would kill billions of people—billions—in the years that follow a large-scale nuclear war, even if it was fought “only” with today’s reduced stockpiles.⁵ 

It is unclear whether humanity as a species could possibly survive a full-scale nuclear war with the current stockpiles.⁶ A nuclear war might well be humanity’s final war.

Close Calls: Instances that threatened to push the ‘balance of terror’ out of balance and into war

The ‘balance of terror’ is the idea that all involved political leaders are so scared of nuclear war that they never launch a nuclear attack.

If this is achievable at all, it can only be achieved if all nuclear powers keep their weapons in check. This is because the balance is vulnerable to accidents: a nuclear bomb that detonates accidentally – or even just a false alarm, with no weapons even involved – can trigger nuclear retaliation because several countries keep their nuclear weapons on ‘launch on warning’; in response to a warning, their leaders can decide within minutes whether they want to launch a retaliatory strike. 

For the balance of terror to be a balance, all parties need to be in control at all times. This however is not the case. 

In the timeline, you can read through some of the close calls during the past decades.

The risk of nuclear war might well be low – because neither side would want to fight such a war that would have such awful consequences for everyone on the planet. But there is a risk that the kinds of technical errors and accidents listed here could lead accidentally to the use of nuclear weapons, as a nuclear power can incorrectly come to believe that they are under attack.

This is why false alarms, errors, and close calls are so crucial to monitor: they are the incidents that can push the ‘balance of terror’ out of balance and into war. 

Accidents and errors are of course not the only possible path that could lead to the use of nuclear weapons. There is the risk of a terribly irresponsible person leading a country possessing nuclear weapons. There is the risk of nuclear terrorism, possibly after a terrorist organization steals weapons. There is the possibility that hackers can take control of the nuclear chain of command. And there is the possibility that several of these factors play a role at the same time.

A timeline of nuclear weapons ‘close calls’⁷

Below this post, you find additional lists of close calls, where you find much more information on each of these incidents.

How to reduce the risk of nuclear war?

An escalating conflict between nuclear powers – but also an accident, a hacker, a terrorist, or an irresponsible leader – could lead to the detonation of nuclear weapons. 

Those risks only go to zero if all nuclear weapons are removed from the world. I believe this is what humanity should work towards, but it is exceedingly hard to achieve, at least in the short term. It is therefore important to see that there are additional ways that can reduce the chance of the world suffering the horrors of nuclear war.⁸

A more peaceful world: Many world regions in which our ancestors fought merciless wars over countless generations are extraordinarily peaceful in our times. The rise of democracy, international trade, diplomacy, and a cultural attitude shift against the glorification of war are some of the drivers credited for this development.⁹

Making the world a more peaceful place will reduce the risk of nuclear confrontation. Efforts that reduce the chance of any war reduce the chance of nuclear war.

Nuclear treaties: Several non-proliferation treaties have been key in achieving the large reduction of nuclear stockpiles. However, key treaties – like the Intermediate-Range Nuclear Forces (INF) Treaty between the US and Russia – have been suspended and additional agreements could be reached.

The UN Treaty on the Prohibition of Nuclear Weapons, which became effective in 2021, is a recent development in this direction.

Smaller nuclear stockpiles: Reducing the stockpiles further is seen as an important and achievable goal by experts. 

It is considered achievable because smaller stockpiles would still provide the deterrence benefits from nuclear weapons. And it is important as it reduces the risk of accidents and the chance that a possible nuclear war would end civilization.

Better monitoring, better control: The risk can be further reduced by efforts to better control nuclear weapons – so that close calls occur less frequently. Similarly better monitoring systems would reduce the chance of false alarms. 

Taking nuclear weapons off ‘hair-trigger alert’ would reduce the risk that any accident that does occur can rapidly spiral out of control. And a well-resourced International Atomic Energy Agency can verify that the agreements in the treaties are met.

Better public understanding, global relations, and culture: Finally I also believe that it will help to see clearly that billions of us share the same goal. None of us wants to live through a nuclear war, none of us wants to die in one. As Reagan said, a nuclear war cannot be won and it would be better to do away with these weapons entirely. 

A generation ago a broad and highly visible societal movement pursued the goal of nuclear disarmament. These efforts were to a good extent successful. But since then, this goal has unfortunately lost much of the attention it once received – and this is despite the fact that things have not fundamentally changed: the world still possesses weapons that could kill billions.¹⁰ I wish it was a more prominent concern in our generation so that more young people would set themselves the goal to make the world safe from nuclear weapons.

Below this post you find resources on where you can get engaged or donate, to help reduce the danger from nuclear weapons.

For eight decades people have been producing nuclear weapons. Several countries have dedicated vast sums of money to their construction. And now we live in a world in which these weapons endanger our entire civilization and our future.

These destructive weapons are perhaps the clearest example that technology and innovation are not only forces for good, they can also enable catastrophic destruction. 

Without the Second World War and the Cold War, the world might have never developed these weapons and we might find the idea that anyone could possibly build such weapons unimaginable. But this is not the world we live in. We live in a world with weapons of enormous destructiveness and we have to see the risks that they pose to all of us and find ways to reduce them.

I hope that there are many in the world today who take on the challenge to make the world more peaceful and to reduce the risk from nuclear weapons. The goal has to be that humanity never ends up using this most destructive technology that we ever developed.

Resources to continue reading and finding ways to reduce the risk of nuclear weapons:

• Hiroshima: John Hersey’s report for the New Yorker about the bombing of Hiroshima, published in August 1946.
• ’80,000 Hours’ profile on Nuclear Security: an article focusing on the question of how to choose a career that makes the world safer from nuclear weapons.
• The ‘Future of Life Institute’ on Nuclear Weapons: this page includes an extensive list of additional references – including videos, research papers, and many organisations that are dedicated to reducing the risk from nuclear weapons.

Acknowledgments: I would like to thank Charlie Giattino, Hannah Ritchie, and Edouard Mathieu for reading drafts of this and for their very helpful comments and ideas.

Additional lists of close calls with nuclear weapons:

• Future of Life Institute – Accidental nuclear war: A timeline of close calls. 
• Alan F. Philips, M.D. – 20 Mishaps That Might Have Started Accidental Nuclear War, published on Nuclear Files
• Josh Harkinson (2014) – That Time We Almost Nuked North Carolina
• Union of Concerned Scientists (2015) – Close Calls with Nuclear Weapons
• Chatham House Report (2014) – Too Close for Comfort: Cases of Near Nuclear Use and Options for Policy authored by Patricia Lewis, Heather Williams, Benoît Pelopidas, and Sasan Aghlani

Wikipedia – List of Nuclear Close Calls

Our World in Data presents the data and research to make progress against the world’s largest problems.
This article draws on data and research discussed in our entry on Nuclear Weapons.

Endnotes

1. On Nuclear Winter see:
   • Jägermeyr, Jonas, Alan Robock, Joshua Elliott, Christoph Müller, Lili Xia, Nikolay Khabarov, Christian Folberth, et al. (2020) – ‘A Regional Nuclear Conflict Would Compromise Global Food Security’. Proceedings of the National Academy of Sciences 117, no. 13 (31 March 2020): 7071–81.
   • Robock, A., L. Oman, and G. L. Stenchikov (2007) – Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences, J. Geophys. Res., 112, D13107, doi:10.1029/2006JD008235.
   • Alan Robock & Owen Brian Toon (2012) – Self-assured destruction: The climate impacts of nuclear war. In Bulletin of the Atomic Scientists, 68, 66–74.
   • Alan Robock & Owen Brian Toon (2016) – Let’s End the Peril of a Nuclear Winter, In the New York Times, Feb. 11, 2016.
2. Some additional points:
   • The risk of nuclear winter (initially termed ‘nuclear twilight’) was only discovered in the early 1980s, more than 3 decades after the bombs were first used.
   • The main mechanism by which a nuclear winter is expected to cause a decline in global food production is by reducing the growing season, the days in a row without frost. See Robock, Oman, and Stenchikov (2007).
   • Robock estimates that the smoke and soot would rise as high as 40 kilometers (25 miles) into the atmosphere. See Robock and Toon (2016).
   • Before the nuclear famine kills people from hunger, many will die from hypothermia.
   • In addition to the impact on the climate, the ozone layer is expected to get depleted in such a scenario. This would allow more ultraviolet radiation to reach our planet’s surface, harming plant and animal life.
   • In general there is only relatively little scientific work that focuses on nuclear winter and additional, good research could be useful to provide a better understanding. Due to the lack of research there remains uncertainty about how devastating a nuclear winter would be. In particular there is disagreement on how likely it is that all of humanity would die in a nuclear winter.
   • The paper by Jägermeyr et al (2020) shows that among the countries with the largest food production losses would be the US and Russia, those countries that have the largest stockpiles of nuclear weapons.
3. For anyone who interested in the impact of nuclear winter on food production and famine, Ord (2020) cites the following:
   • Cropper, W. P., and Harwell, M. A. (1986) – “Food Availability after Nuclear War,” in M. A. Harwell and T. C. Hutchinson (eds.), The Environmental Consequences of Nuclear War (SCOPE 28), vol. 2: Ecological, Agricultural, and Human Effects. John Wiley and Sons.
   • Helfand, I. (2013) – Nuclear Famine: Two Billion People at Risk? Physicians for Social Responsibility.
   • Xia, L., Robock, A., Mills, M., Stenke, A., and Helfand, I. (2015) – Decadal Reduction of Chinese Agriculture after a Regional Nuclear War. Earth’s Future, 3(2), 37–48.
   • Reagan in his State of the Union address in 1984, quoted in the New York Times: Bernard Gwertzman (1984) – Reagan reassures Russians on war. In the New York Times January 26, 1984.
   • There are nine countries that are known to possess nuclear weapons: Russia, United States, France, China, United Kingdom, Israel, Pakistan, India, and North Korea. South Africa once possessed nuclear weapons and is the first state to voluntarily give up nuclear weapons.
   • The explosive power of a nuclear weapon is called the yield of a nuclear weapon. It is the amount of energy released when that weapon is detonated. It is usually measured in ‘TNT equivalents’.
     
     The bomb that the US dropped on Hiroshima had a yield of 13–18 kilotons of TNT. (one kiloton are 1000 tonnes)
     
     The largest bomb that was ever detonated is the ‘Tsar Bomba’ built by the USSR and detonated in October 1961. Its yield was about 50 megatons of TNT. That’s 50,000 kilotons of TNT or about 3,333-times the yield of the bomb in Hiroshima.
   • The scenario in Robock, Oman, and Stenchikov (2007) is based on the nuclear stockpiles after the large reduction that was achieved after the end of the Cold War. It shows that the world still retains enough weapons to produce “a large, long-lasting, unprecedented global climate change,” as the authors put it. Since the publication of this study, the stockpiles have been reduced further, as the chart shows, but not very strongly so.
   • For a recent discussion of this question see Ord (2020) – The Precipice.
   • This list is largely based on Toby Ord’s 2020 book The Precipice. His list can be found in Chapter 4 and Appendix C of his book.
     
     Ord in turn relies mostly on a document from the US Department of Defense from 1981: Narrative Summaries of Accidents Involving US Nuclear Weapons (1950–1980).
   • This list is mostly based on the ’80,000 Hours’ profile on Nuclear Security and Toby Ord (2020) – The Precipice.
   • For big overviews of this literature see the forthcoming book Christopher Blattman (2022) – Why We Fight: The Roots of War and the Paths to Peace and Steven Pinker (2011) – The Better Angels of our Nature for a big overview
   • Lawrence S. Wittner – Confronting the Bomb: A Short History of the World Nuclear Disarmament Movement. Stanford University Press.
     
     One indication for the declining interest in the last generation: Mentions of “nuclear war” in books and newspapers peaked in 1985 and declined strongly since then (see Google Ngram for ‘nuclear war’).