By full-scale war, I mean an exchange of nuclear strikes between the world's largest powers - the United States, Russia and China - each of which will spend its entire arsenal. The total number of warheads today (14,000) is significantly less than at the height of the Cold War (70,000). Although extinction is unlikely today, that likelihood could change if a significant number of new warheads are deployed or the design of weapons changes dramatically.
Three potential mechanisms for the extinction of people after a nuclear war are:
- Kinetic destruction.
- Radiation.
- Changing of the climate.
With existing weapons, only the third point is plausible, but let's look at each of them.
1. Kinetic destruction
There are not enough nuclear warheads to destroy all humans with kinetic effects, and it is unlikely that they will ever exist. There are 14,000 nuclear weapons in the world. Let's say, on average, their capacity will be 1 megaton. And this is a conservative estimate - in reality, the average will be closer to 100 kilotons. A megaton warhead can create a ball of fire covering 3 km2 and a shockwave of medium force that blows away private homes in an area of 155 km2. The ball kills almost everyone, and the wave kills a fairly large percentage of people, but not 100%. Let's take a conservative estimate, and say that the shockwave also kills everyone. 14,000 * 155 = 2.17 million sq. Km. The area of the New York metropolitan area is 8 683 sq. Km. It turns out that all the world's nuclear weapons can destroy 250 such agglomerations. It's a lot! But not enougheven if someone tried to destroy all people at once. The total surface area of the earth is 510.1 million square kilometers. The area of cities is 2%, or about 10.2 million square kilometers. The total area of destruction by nuclear weapons is 2.17 million square kilometers, which is significantly less than the minimum estimate of the area of human habitation, 10.2 million square kilometers. Therefore, kinetic destruction cannot destroy humanity.
Inside the white circle is a zone of moderate shockwave impact (34 kPa): 7.03 km (155 sq km) from the megaton warhead. See the nukemap site.
If you want to check my calculations, I used the Nuke map site .
Even more obvious reasons why the kinetic impact will not destroy humanity is that nuclear powers can threaten one or several countries at once, but not all the central cities of the world. Even if all NATO countries, Russia and China start a war at once, Africa, South America and other neutral regions will not suffer kinetic destruction.
2. Radiation
Radiation will not be able to kill everyone, since there will not be enough weapons for this. Radiation from impacts will concentrate in several places, while in others it will not be at all. And even in the hardest hit regions, lethal radiation from fallout will fall to habitable levels in a matter of weeks.
It is worth noting that there is a relationship between the length of the half-life and the energy released by radionuclides. The shorter the period, the more energy is released, and the longer the period, the less energy. Radioactive fallout from modern weapons kills very quickly, but only for a few days or a few weeks.
From Nuclear War Survival Skills , 1987
Let's do the same calculations that we used in the case of kinetic destruction, and see if it is possible to carry out an attack aimed at maximizing radioactive fallout in order to kill everyone. Using Nukemap, set the border to 100 rad per hour. It is believed that 400 glad kills 50% of people, so 100 glad per hour will surely kill almost all people, not counting those who took refuge in the shelter. It is necessary to switch to detonation at ground level, and not in the air, because in this case, much more radioactive fallout is obtained. An explosion with a power of 1 mt on the ground will create radiation of more than 100 rad per hour on an area of 8000 sq. Km. Multiplying by 14,000 warheads, we get 112 million square kilometers. It's a lot! Still less than 510.1 million sq. Km. land area, but more than 10.2 million square kilometers. urban developments. Apparently, this is enough to cover all the habitats of people,so, in principle, you can kill everyone with radiation from existing nuclear weapons.
Explosion of a 1000 kiloton bomb at ground level. The bright red and red colors represent the contour of radioactive fallout for 1000 rad and 100 rad per hour, respectively, covering an area of 1140 square kilometers. and 7080 sq. km. respectively.
In practice, it is almost impossible to kill all people with radiation from existing nuclear weapons, even if you try to use them for this purpose. First, the distribution of precipitation is very uneven. After the explosion, they are carried by the wind. Some areas will be hit hard, some will hardly be affected. Even if almost all human centers are covered, some regions will be able to avoid this fate.
Two other reasons make extinction due to radiation unlikely. Many countries, especially in the southern hemisphere, are unlikely to be affected by fallout. Most of these countries will take the neutral side, they are not located next to the belligerents, and therefore they will be relatively safe. Precipitation can travel hundreds of kilometers, but still will not reach very distant places. Precipitation that reaches the upper layers of the atmosphere will eventually fall again, but, most likely, already when the radiation ceases to be fatal. Another mitigating factor is that in typical nuclear exchange plans, ground explosions are usually carried out in locations where protected targets are located. In places with dense population and industrial centers, aerial explosions are preferred. The point is that air blasts maximize the shock wave.At the same time, there is not much radioactive fallout after an air explosion, so people living not on the leeward side of military targets, probably, will not be much affected by radiation in case of war.
The last factor protecting against radiation extinction is the large mass separating people and the source of radiation, such as radiation shelters. In a few weeks, the radionuclides in the sediments will decay to a state in which people can survive without shelter. There are many shelters in the world, and you can build even more in a day or two with a shovel, earth and planks. Even if deadly fallout from ground explosions covered all of the most populated areas, many people would survive in shelters.
A discussion of the risks of extinction from radiation caused by nuclear weapons would not be complete without a discussion of two factors: nuclear power plants and radiological weapons. I will briefly dwell on them, however, they will not greatly affect the result.
Nuclear power plants can become targets of nuclear strikes, since they can generate large amounts of nuclear fallout with a long half-life, but less energy per unit time. The main concerns are related to the fact that nuclear power plants and waste disposal sites contain a much larger mass of radioactive material than rockets carry. The danger is the proliferation of highly radioactive nuclear fuel. This risk requires a longer analysis, but in short, although a warhead hitting a nuclear power plant or a waste storage site will indeed create long-lived nuclear fallout, it will still concentrate on a small area. Fortunately, even a nuclear explosion does not scatter nuclear fuel over a distance of more than a few hundred kilometers. It will be terrible if certain regions of the countries are covered with nuclear waste, but this will not increase the risk of extinction.
Radiological weapons are nuclear weapons designed to maximize the spread of lethal fallout rather than destruction. The problem is that such weapons can create precipitation that makes the places of their fall uninhabitable for months or even years. This kind of radiological weapon kills more slowly, but kills. In principle, radiological weapons can kill everyone. In practice, however, the same constraints that apply to conventional nuclear weapons apply to weapons optimized for long-term fallout. It also has its own limitations.
Radiological weapons do not produce more rainfall than standard warheads, they simply generate rainfall with different characteristics. As a result, the amount of radiological weapons required to cover the entire surface of the Earth will make this venture extremely costly (comparable to the cost of the largest nuclear arsenals), and will not serve military purposes. Probably due to its inefficiency in disrupting and destroying manpower when compared to standard nuclear weapons, they have never been developed or deployed in large numbers. Therefore, it represents a theoretical concern, but not an existential risk in the near future. Worry about Russian statements about development of unmanned nuclear torpedohigh power (up to 100 Mt), which, in theory, can be used as a radiological weapon. But, even if such devices are put into operation, it is unlikely that enough of them will be produced.
3. Climate change
Most of the risks of human extinction from a nuclear war are associated with the risks of catastrophic climate change, nuclear winter, and the consequences of nuclear explosions. However, even in the scenario of a full-scale war, its final impact on the climate is unlikely to lead to the extinction of humanity.
Because:
A) In the scenarios of the onset of a severe nuclear winter, described by Robock and his team of co-authors, part of the population is likely to survive.
B) Robock's models probably overestimate risks.
C) Nuclear war planners are aware of the risks and include them in the targeting plans for strikes.
Before diving into each of the points, it is worth understanding where the nuclear winter research came from. In the 1980s, a team of atmospheric experts hypothesized that nuclear war would lead to firestorms in cities that would lift small particles into the atmosphere, causing catastrophic cooling that would last for years. Many worried that such an effect is possible, the risk exists, but it has not been noticed for many decades. Some scientists believed that the effect of this event was exaggerated or it was unlikely to happen at all. Until a few years ago, in the peer-reviewed literature, one could find only works predicting the onset of the harsh consequences of a winter after a nuclear war. Naturally, many believed that this was the scientific consensus. However, this is a misinterpretation of uncertainty,available in the scientific community about the risks of nuclear winter. Not many works have been published on this topic (probably no more than 15), and mostly by one group of researchers, despite the existential importance of this topic.
I am delighted that Robock, Thun and others have studied the effects of nuclear winter for most of their careers, and their models are useful in assessing the potential climate change resulting from this phenomenon. However, over time, I have less and less faith in the correctness of Robock's model. See section B) below for details. However, I am not sure what the likelihood of a significant cooling effect from a nuclear war is, and I am still concerned about the potential for a significant cooling of the planet, even if the risk of extinction associated with such events is small.
A) In the scenarios of the onset of a severe nuclear winter, described by Robock and his team of coauthors, part of the population is likely to survive
The most recent and detailed models of potential cooling effects of a full-scale nuclear exchange are contained in the shy and the other titled "Return to nuclear winter with modern climate models and current nuclear arsenals: consequences are still catastrophic."
The effects described in these models are severe. In one of the cases they considered, summer temperatures in the northern hemisphere are 10-30 ° C lower than usual. At the equator, the fall is not so severe (5 ° C), but, in fact, it will affect the entire globe. The most likely outcome will be most people starving to death. Many will also freeze, but hunger is probably a greater risk. Even according to this model, it turns out that in the equatorial regions of the planet it will be possible to grow food, which will be enough for the survival of part of the population. And in 10-15 years, agriculture can be conducted, on a limited scale, in most of the planet.
The average change in air temperature for June, July and August in the year when the ash rises into the air, and the next year after that
Karl Schulman askedone of the authors of the work, Luc Oman, on the likelihood that in the described scenario of a nuclear war humanity will die out. He got the answer "somewhere in the region of one chance in 10,000 or 100,000." This seems likely to me, although expert opinion alone cannot replace deep analysis. At one time, Oman explained its reasoning.
To calculate the chances of human extinction from a nuclear war, two different analyzes are required. The first is an analysis of climate change that could occur due to a nuclear war, and the second is the ability of groups of people to adapt to these changes. I did not come across a deep analysis of the second question, but I think it would be worthwhile to carry out it.
It seems to me that people are able to survive even with much more serious climate changes than those described in the scenarios of a nuclear war. Among mammals, humans are most resistant to sudden changes in temperature, as evidenced by our ubiquity even in prehistoric times. Although the loss of most of the agriculture will surely lead to the death of most of the people on Earth, modern technology will allow some populations to survive. There are huge reserves of food in the world, and it is likely that some of them will take over and protect small groups that will have enough food for years. And while even they won't have enough food for 10-15 years, these supplies will give them time to adjust to new sources of food. ALLFED has explored many alternative food sources,capable of keeping populations alive in the event of a nuclear war or other problems with sunlight, and it seems to me that there is a serious need to find even more of them in the event of such a disaster.
B) Robock's models likely overestimate risks
Simply put, the nuclear winter model looks like this: nuclear explosions → urban fires → urban firestorms → soot rises into the upper atmosphere → soot remains in the upper atmosphere, reflecting sunlight and leading to massive cooling.
Each of the steps is required for the effect to occur. If a nuclear war causes large-scale fires in cities, but does not lead to the appearance of firestorms that lift particles upward, then no long-term cooling will occur. Some of these steps are easier to model than others. From the various papers I read, I concluded that the biggest uncertainties are associated with the following processes:
- the dynamics of burning cities after a nuclear attack;
- the likelihood of fire storms strong enough to lift a large enough number of particles into the atmosphere;
- will they lift these particles high enough for the particles to remain there for years.
We are finally seeing a healthy discussion of these issues in the scientific literature. Alan Robock's group published their work in 2007 and described the significant cooling effects caused by limited regional warfare. The Reisner group from Los Alamos published their work in 2018 , where they revised some of the assumptions of the Robock group, and concluded that in such a scenario, a global cold snap is unlikely. Robok replied to this work, and Reisner repliedto the answer. Both authors have sound arguments, but Reisner's position seems more convincing to me. Those wishing to delve deeper into this issue should read this exchange of views. Unfortunately, Reisner's group did not publish an analysis of the potential cooling effects of a full-scale modern nuclear weapons exchange. Still, it is not difficult to extrapolate Reisner's model and see that the cooling will not be as strong as predicted by Robock's model in a similar situation.
C) Nuclear war planners are aware of the risks and include them in plans for determining the targets of strikes
The easiest way to mitigate the risks of a nuclear winter is to refrain from attacking cities with nuclear weapons. The alleged mechanism of its offensive is associated with the burning of cities, and not with ground explosions aimed at military targets. I have spoken with some of the US officials in charge of planning a nuclear war, and they are well aware of the potential risks of a nuclear winter. Naturally, what they know about the risks does not guarantee that they have calculated everything correctly or taken them into account when planning. However, good awareness of the risk increases the likelihood that planners will take steps to minimize the risk of climate effects.
It is difficult to say to what extent all this is taken into account. The plans for nuclear wars are classified. As far as we know, in current plans for the US war, cities are considered targets under certain conditions (but not all). However, Defense Department officials have access to classified information and models that we, civilians, do not have access to. I am sure that nuclear war planners have thought well of the risks of climate change caused by nuclear war, although I am not aware of their conclusions or bureaucratic constraints. All other things being equal, knowledge of these risks by planners reduces the likelihood that they will accidentally allow human extinction.
Conclusion
The article discusses three plausible mechanisms for the extinction of humanity as a result of nuclear war. That one of them, nuclear winter, was not described until the 1980s is a good reminder that we may not know something. Although in nuclear tests we received information about how these weapons work, the situation during the tests is significantly different from the situation during the war. The model remains highly uncertain. Given that the greatest threat to existence comes from climate impacts, it would be great to see more research on the climatic effects of nuclear war and the survival potential of different groups of people.
There seem to be various ways to reduce the existential risk of nuclear war. If, at the planning level, the most powerful weapons are not directed at most of the cities, this will reduce the risk of accidental destruction of humanity. Also, the vulnerability of humankind to nuclear winter can be reduced by improving the survivability of the most favored groups of people. This same tactic can help protect other existential risks as well.
Further reading:
- Quantification of the extinction risk from Toby Orda .
- Nuclear war as a risk of global catastrophe .
- Nuclear Winter and Human Extinction: An Interview with Luke Oman .
- Nuclear winter as a reaction to a nuclear war between the US and Russia in the 4th version of the climate model of the whole atmosphere and the model of the Goddard Institute for Space Research.
- Climate impacts of regional nuclear exchange : improved estimates based on detailed source counts.
- Commentary on Climate Impact of Regional Nuclear Exchange: Improved Estimates Based on Detailed Source Counting by Reisner et al.
- Reply to comment from Robock et al.
- Comparing Economic and Agricultural Models : Climatic and Agricultural Consequences of Nuclear War.