Nuclear Winter and Omnicide

Sometimes people wonder why understanding the Cold War is important. Given the large numbers of nuclear weapons that still exist, this 1983 comment from Carl Sagan probably explains it better that anything:

“Imagine a room awash in gasoline, and there are two implacable enemies in that room: One of them has 9,000 matches, the other has 7,000 matches. Each of them is concerned about who’s ahead; who’s stronger. Well, that’s the kind of situation we are actually in.”

– Carl Sagan talking about the Cold War nuclear balance between the US and USSR on ABC in 1983 (1).

Can We Survive Nuclear War? In all but some limited cases, the answer to this question rapidly becomes ‘no’.

This truth is not openly discussed by the governments of nuclear-armed States with their general populations, for the simple reason that it would likely lead to demands for nuclear disarmament. Whilst many people outside of the blast and flash zones of a nuclear explosion could survive the immediate effects of a nuclear attack, as soon as a so-called ‘nuclear exchange’ involves more than a small number of these weapons being used, most of those survivors then become at risk of a protracted death during the nuclear winter that would follow.

So… What is a Nuclear Winter?
What could come after the flames had died down would be far worse than the fire itself.

Sagan decided to spread news of the discovery of the possibility of a nuclear winter occurring via the media, rather than relying on academic reporting and politicians to take the discovery seriously by themselves. He was very clear about what the results of the research into nuclear winter were showing:

“… If Nation A makes a massive attack, for whatever reason, on Nation B… Nation B doesn’t do anything to defend itself or to retaliate… nevertheless the smoke that gets raised over Nation B circulates around the world, covers Nation A.

“Nation A gets cold and dark, and the agriculture fails and Nation A has destroyed itself by launching a nuclear war on Nation B.

“The main consequence of nuclear winter is massive agricultural failures… the net result in mass starvation can account for many billions of lives…

“So it now appears that nuclear war certainly will destroy the nation’s involved, almost certainly will destroy the global civilization and might just possibly destroy the human species… nuclear war has put us in a position to do utter devastation to our species.” (2)

The ‘TTAPS study’
Earlier modelling of the effects of nuclear explosions had focussed on the direct blast, heat, radiation and fallout. The indirect and longer-term effects on the environment were ignored. In part this is because the computer power required for those models was not yet available, but including them would have significantly reduced “… the number of USAF warheads and vehicles required to achieve the designated damage levels.”(3)

Casualty estimates from US war plans developed by SAC and the Joint Chiefs were a ‘fantastic underestimate’ and deliberately ignored the effects of fire, even though “… the firestorms caused by thermonuclear weapons were known to be predictably the largest producers of fatalities in a nuclear war.”

The phrase ‘nuclear winter’ was first used in a 1983 report from the ‘TTAPS study’ (named after authors’ surnames: R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, and Carl Sagan) (4).

It showed how burning petroleum fuels and plastics in nuclear-devastated cities would inject soot into the stratosphere in sufficient volumes to block most direct sunlight from reaching the surface, causing global cooling, widespread crop failures and famine.

Sagan’s decision to publicise the TTAPS results in the 30th October 1983 issue of ‘Parade’ magazine placed the concept of ‘Nuclear Winter’ into the public consciousness (5). Suddenly people were hearing how even a small, ‘limited nuclear exchange’, could be enough to kill most things living on the surface of the planet.

The new ‘nuclear winter’ computer models used information gathered from natural, widespread wildfire-firestorms, as well as the Allies’ non-nuclear bombing of Hamburg in 1943, and the nuclear bombing of Hiroshima in 1945. In those 2 latter cases it was possible that soot may have been injected into the stratosphere, making them good research examples.

The scenario for triggering a nuclear winter looked like this (6):

  • 100 or more city firestorms are ignited by nuclear explosions,
  • Large volumes of sooty smoke are lifted into the upper troposphere and lower stratosphere,
  • Absorption of sunlight in the lower stratosphere further heats this soot, lifting some or all of it higher into the stratosphere, where it could persist for years before being rained out,
  • These suspended sooty particles cause ambient light levels to fall to “… a few percent of ambient”, and “… land temperatures can reach -15 ° to -25 °C”.

As a result “… long-term exposure to cold, dark, and radioactivity could pose a serious threat to human survivors and to other species.”

That sounds rather clinically understated.

Even during the Little Ice Age global temperatures were only around 0.5°C colder than normal (7).

Given the huge nuclear arsenals held by both Russia and the United States, if a nuclear war were to occur and “high value” metropolitan areas were targeted, it is more than likely that absolutely everything would burn and be destroyed. Joshua Coupe, an atmospheric science doctoral candidate at Rutgers University said that “even asphalt can burn at the temperatures these bombs get to” (8).  The sooty smoke produced in those fires would be very buoyant, rising high into the atmosphere where it could absorb solar insolation very effectively, driving the environment into a nuclear winter.

New Scientist magazine expressed the impact on the UK in very direct terms in their 13th Sept 1984 issue: “… we would be reduced to a hunter-gather life style, with nothing to hunt and precious little to gather.” (9)

When the news broke to the public, the US government and military scientists were already downplaying it, arguing that the effects would not be nearly as devastating, and even described the possibility of it as being more like a ‘nuclear autumn’. (10)

Sagan and Turco followed up the publication of their study with a book in 1990 called ‘The Path Where No Man Thought’. Their aim was to make people aware of the facts about a nuclear winter, describing how the severity depends on the number of warheads used and what was targeted. Once again the nuclear winter scenario made front-page headlines for a while, and it recently had a further resurgence in 2019, with new information coming to light. (11)

The apocalyptic nuclear winter hypothesis was quickly embraced by the disarmament movement, causing a problem for the military-industrial complex in nuclear-armed states and the preservation of their nuclear stockpiles.

Other Studies & How Cold Is A Nuclear Winter?
In 1986, Robert Malone (a scientist at the Los Alamos National Laboratory) and his colleagues created the ‘General Circulation Model’, which is widely considered to be the most sophisticated available. They said that:

“…for a summertime war that results in a large injection of smoke…our model predicts temperature changes of between 10 to 15 degrees C. below normal in the interiors of large continents in the northern hemisphere”.

That effect is “substantially less” along the coasts of countries and in the southern hemisphere. The effects are also less if the war happened in the winter, as the weaker insolation would be insufficient to lift the soot into the upper troposphere (see “‘Nuclear Winter’ Comes In From The Cold”).

In 1989, Alan Robock and Brian Toon used a NASA computer model to show that even if less than 1% of the global nuclear arsenal was used on the other side of the world, global food production would decrease by around 30% for five years, and then by around 15% for a further five years. (12) 

Throughout the 1990s, following the failed predictions of the effects of the Kuwait oil fires in 1991, no new papers were published on the topic. Recently, however, the same team of computer modellers from the 1980s began to publish the outputs from new computer models, producing the same general findings as the older ones. They still find that the ignition of 100 firestorms, each one comparable to that experienced in Hiroshima, could lead to a ‘small’ nuclear winter.

A paper from Mills et al. in 2014 (13) showed that even a regional nuclear war involving the detonation of 100 x 15Kt weapons over cities resulted in:

  • the coldest average surface temperatures in the last 1000 years,
  • growing seasons reduced by 10-40 days per year for five years, and
  • surface temperatures would be reduced for over 25 years.

Pollution from PCBs, asbestos, dioxins and other chemicals would make the air so contaminated it would be hard to breathe, whilst these harsh conditions would leave no biodiversity to turn to in the oceans (14). Would survivors have the psychological strength left to even want to exist at this point?

A slight chance of avoiding omnicide?
It was once considered that a nuclear war and subsequent winter could have the potential to wipe out the entire human race, in essence omnicide bya doomsday weapon.

However, despite apocalyptical tales like ‘On the Beach’ (Nevil Shute, 1957), scientists now somewhat lean in favour of certain isolated countries like Australia and New Zealand as being possible places of survival. Scientists also believe that the Earth would not experience another ice age as a direct result of a nuclear winter. 18,000 years ago North America was covered with sheets of ice, up to 3 km thick, which took thousands of years to build up from annual snow layers. The climate disruptions arising from a nuclear war would not last long enough to produce similar ice sheets.

A number of approaches have been explored for reducing the severity of a nuclear winter or mitigating its risk to human survival. Perhaps I am being somewhat negative to feel that these range from the downright insane, through the pointless, to our species stumbling in the ‘Last Gasp Saloon’.

The ‘downright insane’ includes a 1967 plan to create firebreaks in order to “… minimize casualties and property damage from urban mass fires” – so far, so good. Then comes the idea of making the firebreaks with ‘subsurface nuclear explosives’ (section 4, 4.1.3), including the possibility of detonating these nuclear explosives “… in a row of holes drilled before attack” – oh dear (15).  Having destroyed much of the populated world with nuclear weapons, the US Naval Radiological Defense Laboratory’s answer was to fix the problem with yet more nukes!

Given that the prevailing US war plan was to pre-emptively launch the entire nuclear arsenal at Russia and China if a nuclear attack from them (principally Russia) looked imminent – who would be drilling the holes and laying what remaining nuclear explosives?

There is perhaps more merit in exploring ways to maintain a food and water supply for the shorter durations of nuclear winter that are now being modelled. This includes options for eating fungi, the edible inner bark of trees, seaweeds or cold-weather crops shifted to grow near the equator (16). Other plans involve increased levels of food stockpiling. But with years of food being needed, are these ideas really practical?

Closing thoughts: In the early years of the Cold War only 2 countries had nuclear weapons (USA and Russia), now nine countries do (17).  Unless there is a major global shift to nuclear disarmament, the threat of a nuclear winter will not go away.

Ellsberg writes that “… U.S. plans for thermonuclear war in the early sixties… would have killed many times more than the six hundred million people predicted by the JCS. They would have starved to death nearly everyone then living: at that time three billion people.

The numbers of warheads in the possession of the U.S. and Russia have since declined. Yet according to the most recent scientific calculations, even a fraction of the existing arsenals would be enough to cause nuclear winter today.”

He suggests that it is the vulnerability of land-based silos, with their missiles kept in a state of ‘launch on warning’ (ie ready to go, every hours, of every day of the year)  that creates the greatest risk of a catastrophic error and nuclear winter.

Eliminating land-based missiles would greatly reduce the risk of omnicide. However, as I write this article in 2020, the superpowers seem to be heading in the opposite direction, creating new classes of weapons and withdrawing from arms control treaties. It would only take one accident or misinterpretation of events to start a ‘nuclear exchange’ that could ultimately destroy most life on Earth.


1 – “Carl Sagan on the Nuclear Arms Race (1983)” –

2 – “Carl Sagan explains consequences of a nuclear winter” – TV interview –

3 – “The Doomsday Machine” – Ellsberg, Daniel. (p. 140-141) – Bloomsbury Publishing. Kindle Edition

4 – “Nuclear winter” – Encyclopedia Britannica – and “Nuclear Winter: Global Consequences of Multiple Nuclear Explosions” – Science –

5 – “When Carl Sagan Warned the World About Nuclear Winter” – Smithsonian Magazine –

6 – “Nuclear Winter” –’s_Tale_page_242-244-16

7 – “Little Ice Age” – 

8 – “Nuclear Winter May Bring a Decade of Destruction” –

9 – “Not with a bang but a winter” – Mick Kelly – New Scientist Magazine – 13th September 1984

10 – “Does anybody remember the Nuclear Winter?” –

11 – “‘Nuclear Winter’ Comes In From The Cold” –

12 – “Nuclear Winter with Alan Robock and Brian Toon” –

13 – “Multidecadal global cooling and unprecedented ozone loss following a regional nuclear conflict” – Mills, Toon, Lee-Taylor and Robock – Earth’s Future, AGU Publications, 1st April 2014

14 – “Nuclear Winter” –

15 –  “Countermeasure Concepts for Use Against Urban Mass Fires From Nuclear Weapon Attack” –  W. E. Shelberg and E. T. Tracy. U.S. Naval Radiological Defense Laboratory, San Francisco, California 1967 –

16 – See links at

17 – “Nuclear Weapons: Who Has What at a Glance” – Arms Control Association –

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