Kurzgesagt – In a Nutshell
Sources and further reading – Nuclear Winter
This video was supported by Open Philantrophy. If you want to know what you can do to reduce the risk of nuclear war, check out this list of further reading links provided by their network of experts:
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Learn more:
Nuclear winter - Reviewing the evidence, the complexities, and my conclusions is a decent EA forum post, which digs into the weeds about how hard it is to model nuclear winter.
Coupe et al., 2019: On the nuclear winter effects of 150 Tg soot injection to the stratosphere.
Reisner et al., 2019 and Reisner et al., 2018 which concludes regional nuclear war is unlikely to cause nuclear winter.
Pausata et al., 2016: On how long soot lasts based on how abruptly it is emitted into the stratosphere.
Some policy Implications of Nuclear Winter (RAND 1985)
Niel Halloran on nuclear winter (RAND 2022)
Nuclear weapons: Why reducing the risk of nuclear war should be a key concern of our generation
We thank following experts:
Prof. Matt Caplan
Illinois State University
Prof. Brian Toon
Laboratory for Atmospheric and Space Physics
University of Colorado Boulder
Prof. Lili Xia
Rutgers Impact Studies of Climate Intervention (RISCI)
Rutgers University-New Brunswick
The calculation of the effects of a nuclear war are extremely complex. Numerous factors have to be taken into account, such as the number of nuclear weapons, detonation sites, seasons, population distribution, vegetation and much more.
Various models are used for this, e.g. climate models to simulate climate changes or the distribution of soot in the atmosphere. There are also methodological differences in other aspects, e.g. in the calculation of the amount of soot.
You will therefore find different models and approaches in the sources because they differ, for example, in methodology or are at different stages of development. Depending on the study, there are therefore also differences in the results and conclusions. However, these differences are usually very detailed and small-scale. Regarding the overall conclusion, i.e. a drastic or less drastic influence on the climate, there is, however, consensus between the various studies.
– When a nuclear weapon is detonated, a bubble of gas hotter than the sun is forced into existence, so hot that everything within kilometers immediately begins to burn. The terror bubble expands rapidly, filling the sky over its target, creating a devastating shockwave that causes most of the immediate destruction. Basically you break a lot of stuff and set it on fire – and in the worst case this turns into a firestorm that consumes everything and everyone on the ground.
Right after the explosion a gigantic mushroom cloud rises over the destruction like a demon throning over its perverse work, but in the following hours a far more deadly cloud forms. The fire burning cities, forests or fields, heats up so much air that it creates its own micro climate and wind system. Hot air and hot smoke rise, pulling in fresh air from the surroundings, and fresh oxygen stoking the flames even more.
In an earlier video, we showed in detail what happens in an atomic bomb explosion.
#Kurzgesagt (2019): What if We Nuke a City?
https://www.youtube.com/watch?v=5iPH-br_eJQ
In the source for this video you will find this comprehensive publication:
Glasstone, S. & Dolan, P. J. (1977): The Effects of Nuclear Weapons
– This creates an updraft and forms a colossal pyrocumulonimbus cloud that carries the soot and aerosols from the flames high into the stratosphere.
Under normal conditions, the soot rising from a big fire is quickly washed out by rain. But a pyrocumulonimbus cloud can reach altitudes well above the height where rain clouds form. Once above the tropopause, there is simply no weather to remove soot from the atmosphere, so it can stay aloft for years.
Put simply, these clouds form during large fires such as wildfires or volcanic eruptions.
In the context of an atomic bomb explosion, however, they should not be confused with the mushroom cloud.
Due to the great heat within the cloud, less condensation and thus rain takes place, so that "washing out" of the soot is suppressed.
Small components in the air normally act as condensation nuclei from which rain is formed and which then fall to the ground with the rain. However, when the cloud reaches the stratosphere (at an altitude of about 15 km), this process comes to a stop due to the lack of water in the air that could condense on the soot.
#Spencer, S. (2022): Nuclear Winter and the Anthropocene. GSA Today, Vol. 32 (8)
https://www.geosociety.org/GSA/Publications/GSA_Today/GSA/GSAToday/science/G538A/article.aspx
Quote: ”Pyrocumulonimbus (pyroCb) clouds produced by rising hot air and smoke from large wildfires can inject smoke into the upper troposphere and lower stratosphere (Fromm et al., 2010, 2021). PyroCb clouds are similar to typical thunderstorm clouds and form under similar conditions (Fig. 2B), but they receive an extra boost from hot air rising above a fire (Fromm et al., 2006; Rodriguez et al., 2020). Rainout of smoke due to water condensation on smoke particles is suppressed because of the warmth of the pyroCb cloud, the rapid ascent rate of heated air, and the small size of the abundant water-condensation droplets (Rosenfeld et al., 2007). As a result, smoke particles in large pyroCb clouds are effectively delivered to the upper troposphere and lower stratosphere.
Unlike volcanic aerosols and wind-blown mineral dust, the black carbon (soot) content of smoke absorbs sunlight and warms the surrounding air, which can result in gradual rise in a process called “self-lofting.” In nuclear-winter scenarios, convective ascent of smoke to the upper troposphere and lower stratosphere is followed by self-lofting to higher altitudes in the stratosphere where very low water content prevents condensation and particulate rain-out. Furthermore, the black carbon component of smoke is highly resistant to degradation by sunlight and can have a residence time of months to years in the stratosphere (Peterson et al., 2021).”
– If this happens to a single city, it’s a tragedy, but a fairly local one. But in a full scale nuclear war, warring nations following the cold logic of mutually assured destruction, could use hundreds or even thousands of nuclear weapons all at once, creating hundreds of fire storms, sending up to 150 million tons of soot, a cube the size of a skyscraper, directly into the stratosphere.
For this calculation we need the density of ash. Since all kinds of things burn in a nuclear war, the type of ash naturally varies. For the purpose of simplicity, we take a density value (ρ) of 1g/cm3 and calculate the side length (L) of a cube:
L = (M/ρ)(1/3) = (1506 t / (1g/cm3))(1/3) ~ 530 m.
#Mills, M. J. et al. (2014): Multidecadal global cooling and unprecedented ozone loss
following a regional nuclear conflict. Earth’s Future, Vol. 2(4)
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013ef000205
Quote: “We assume a mass density of 1 g cm−3 for each BC particle, consistent with measurements of atmospheric BC particles collected on filters, which are composed of smaller, denser particles aggregated in fractal formations with spatial gaps [Hess et al., 1998].”
Sitarz-Palczak, E. (2018): The Physicochemical Properties and Composition of Biomass Ash and Evaluating Directions of its Applications. Polish Journal of Environmental Studies, Vol. 27 (6)
Quote: “The bulk density of analyzed biomass ash in an uncompressed state (and density state) decreases from 0.94 to 0.71 g/mL (1.35 to 1.11 g/mL) along with decreasing waste grain diameter (Fig. 1b).
– In the next few days and weeks the soot begins to blanket the earth at high altitudes, absorbing light high above the ground and preventing sunlight from reaching the surface . This is not like science fiction where the sky turns dark and the sun disappears.
Here you can see snippets of the global distribution of ash after a full-scale nuclear conflict between the USA and Russia. A complete animation can be found here: https://climate.envsci.rutgers.edu/nuclear/BCdaily150tg.gif from:
#Robock, A. (retrieved 2023): Climatic Consequences of Nuclear Conflict
Nuclear Winter is Still a Danger
#Toon, O.B. et al. (2007): Atmospheric effects and societal consequences of regional scale nuclear conflicts and acts of individual nuclear terrorism. Atmospheric Chemistry And Physics, Vol. 7 (8)
https://acp.copernicus.org/articles/7/1973/2007/
Quote: “Here we have estimated the mass of elemental carbon (also referred to as light absorbing carbon, soot, and black carbon) emitted by the fires. Most treatments of atmospheric aerosols subdivide smoke into elemental carbon, which is assumed to be absorbing at visible wavelengths, and other components, which is meant to represent materials in the smoke that do not absorb sunlight. The elemental carbon has a greater impact on climate per unit mass than the other components because it absorbs light rather than simply scattering it, but the other materials can also enhance the absorption by the elemental carbon.”
– How bad nuclear winter would be is still an active area of research. It all hinges on one thing: how much stuff will burn really hot? How many firestorms would be caused by the heat of the explosions? This depends on many factors, from the materials a city is made of, to the time of the year, if a forest is nearby and so on. So just keep in mind we are working with some assumptions.
In the quotes below, we can only give a brief insight into which factors need to be taken into account and how complex it is to make appropriate predictions.
#Coupe, J. et al. (2019): Nuclear Winter Responses to Nuclear War Between the United States and Russia in the Whole Atmosphere Community Climate Model Version 4 and the Goddard Institute for Space Studies ModelE. JGR Atmospheres, Vol. 124 (15)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030509
Quote: “There are many uncertainties in computing the climate after a nuclear conflict. The greatest uncertainty is how many weapons would be used, what yields would be employed, and which targets would be chosen. This uncertainty cannot be reduced, so ideally, a range of scenarios must be considered to understand the full spectrum of impacts. Using the high-end scenario from Robock, Oman, and Stenchikov (2007), we assume a war between Russia and the United States, involving numbers of weapons allowed under current treaties. The area burned, the amount of fuel available, the amount of smoke and black carbon produced by the fires, as well as the injection altitudes of the smoke, are also uncertain.
(...)
The climate response and smoke removal mechanisms may also differ between models.
#Toon, O. B. et al. (2019): Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. Science Advances, Vol. 5 (10)
https://www.science.org/doi/10.1126/sciadv.aay5478#abstract
Quote: “2. The fuel loading in the fire zone is determined using a recent population database (20) by allocating to each person in the area burned 11,000 kg of flammable material consisting of construction materials, furnishings, clothing, asphalt roofs, plastics, fuels, and other flammables in their homes, places of work, schools, stores, gas stations, and so on.”
– Here is the good news: Nuclear winter is not permanent, and definitely no new ice age. The effects on the climate only last as long as the soot remains in the atmosphere, which is at most a decade or so until it clears out and temperatures normalize.
With decreasing amounts of ash in the atmosphere (fig. 4), decreasing effects on the climate can also be expected (fig. 7). It should also be mentioned, however, that the effects can also be expected to "run on" with the more or less complete removal of ash from the atmosphere over a number of years. For example, precipitation and temperature still appear to be several years below pre-nuclear war levels.
#Coupe, J. et al. (2019): Nuclear Winter Responses to Nuclear War Between the United States and Russia in the Whole Atmosphere Community Climate Model Version 4 and the Goddard Institute for Space Studies ModelE. JGR Atmospheres, Vol. 124 (15)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030509
Quote: “The time evolution of the total amount of soot in the atmospheric column, or soot burden, as simulated by WACCM4 and ModelE is illustrated in Figure 4. Additionally, the soot optical depth in the visible band, which is calculated at 500 nm in WACCM4, is shown. The initial injection of soot is followed by a gradual decline over the course of a decade.”
– In this new climate our seasons are suddenly all wrong. Winters are much longer, summers shorter and colder – or gone altogether. This also means less evaporation over the oceans, which means less rain and maybe large scale droughts.
We have already discussed temperature changes above.
The change in precipitation is shown in the following graph: The brown fields indicate a decrease in precipitation. In some places in the world, this can be as much as 75 to over 90% (e.g. in the USA or Russia).
#Coupe, J. et al. (2019): Nuclear Winter Responses to Nuclear War Between the United States and Russia in the Whole Atmosphere Community Climate Model Version 4 and the Goddard Institute for Space Studies ModelE. JGR Atmospheres, Vol. 124 (15)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030509
Quote: “Aerosol-forced reductions in solar heating, evaporation, and convection diminish precipitation globally, which is found in both the WACCM4 and ModelE simulations, as seen in Figure 7 and discussed by Robock, Oman, and Stenchikov (2007). Figure 7 shows the global precipitation response in both models over the course of 10 years, where there is agreement in an immediate, 30% decline in global precipitation through the first few months of the soot injection. Through Years 2–8 the WACCM4 simulation, compared to ModelE, has 10% less (−0.3 mm/day) precipitation. The maximum reduction of globally averaged precipitation in WACCM4 is 58% and in GISS ModelE is 47%, both during the end of Year 3 and beginning of Year 4.”
– The majority of humanity lives in an area called the midlatitudes, a strip of land that has the ideal temperature for our species – not just because it is not too hot or cold, but it’s also where the plants we eat grow best.
#Moon, J. et al. (2017): An introduction to mid-latitude ecotone:
sustainability and environmental challenges. Siberian Journal of Forest Science, Vol. 6
https://pure.iiasa.ac.at/id/eprint/15033/1/Moon%20J.%20et%20al_SJFS_NO6.pdf
Quote: “The mid-latitude zone can be broadly defined as part of the hemisphere between 30°–60° latitude. This zone is home to over 50 % of the world population and encompasses about 36 countries throughout the principal region, which host most of the world’s development and poverty related problems.”
The vast majority of the food we eat stems from a few highly efficient crops, that are mostly produced in a few very agriculturally productive regions, like the US Great Plains or Ukraine. From these bread and rice baskets of the world, they get traded and shipped around the world.
The graph shows that five of the six most important grain production sites (“bread baskets” are located within temperate latitudes (30° - 60° latitude north).
For some crops, such as soy or corn, more than 30% of total production is in the USA, for example.
This graphic is based on data from the FAO (Food and Agriculture Organization of the United Nations), you can view it here and look at further figures.
#Woetzel, J. et al. (2020):Will the world’s breadbaskets become less reliable? Climate risk and response: Physical hazards and socioeconomic impacts. McKinsey Global Institute
– In the worst case of a full scale nuclear war the temperatures in the midlatitudes will probably stay below freezing for several years.
The first graph shows the temperature differences ("anomaly") compared to normal values.
The top two show the differences in the December-January-February (DJF) year 0-1, the bottom two and June-July-August (JJA) in year 1. There are seasonal variations as well as differences on the surface itself. The interior of the continents is more strongly affected, as the temperature-balancing effect of the oceans cannot be as effective there. The diagram also shows that the southern hemisphere is not so strongly influenced, which is partly due to the polar vortex.
#Coupe, J. et al. (2019): Nuclear Winter Responses to Nuclear War Between the United States and Russia in the Whole Atmosphere Community Climate Model Version 4 and the Goddard Institute for Space Studies ModelE. JGR Atmospheres, Vol. 124 (15)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030509
Quote: “Regardless of season, the largest temperature change is observed over continents. A seasonal bias in the global mean surface temperature, which is obvious from the seasonal cycle from Figure 7, is observed due to the larger fraction of land mass in the NH, which allows larger temperature swings than the ocean.
(...)
The difference in the temperature response between DJF and JJA shrinks rapidly in the ModelE simulation after Year 3 as the oceans are responding to the forcing and the forcing itself becomes smaller, reducing the amplitude of the seasonality in the response. Cooling is less significant in the Southern Ocean in both models (see JJA in Figure 9), because the Antarctic polar vortex is strengthened, causing a poleward shift in winds, which reduces the surface westerlies and vertical mixing (Robock, Oman, Stenchikov, Toon, et al., 2007).
(...)
There is a true nuclear winter in both of these simulations, where temperatures drop below freezing over much of the NH during the height of summer. Figure 9 shows temperature anomalies for WACCM4 and ModelE during the second NH summer after the injection (JJA Year 1), one of the coldest summers after the injection. Continental North America and Eurasia are 20 K or more below average for up to three summers after the soot injection. Temperature changes of this magnitude would lead to below freezing summer temperatures for much of the midlatitudes. The red line shown in Figure 9 represents locations, poleward of which the actual temperature is below 0 °C during JJA Year 1, which shows a shift as far south as northern Texas, Arkansas, and Missouri in the United States, imperiling important agricultural areas during that summer.
(...)
Temperatures below 0 °C in midsummer cause a near 90% reduction in the growing season in some locations, defined here and in Robock, Oman, and Stenchikov (2007) as the number of consecutive days with minimum temperatures above freezing. Figure 10 shows the length of the growing season (number of consecutive days with minimum nighttime temperatures above 0 °C) in the control run and for Years 1 to 2 in the 150-Tg soot injection run. In the NH, the growing season is measured from 1 January to 31 December and the Southern Hemisphere is from 1 July to 30 June. The length of the growing season drops below 50 days across much of the interior United States and below 100 days for the most agriculturally productive regions in the U.S. Most of Eastern Europe's growing season is reduced below 50 days, and all parts of Russia have their growing season reduced below 25 days. Hard freezes, where temperatures drop below −4 °C, would occur through Years 2 and 3 in the summer, making it impossible to grow crops in the United States and Russia. Ukraine, Poland, and Germany would suffer similar fates, while in China, only the southeast part of the country would stay above freezing during the summer. WACCM4 produces slightly colder temperatures than ModelE, but the temperature in both simulations would be perilous for agriculture.”
– Humanity has only a few weeks' supply of crops and food, not enough to survive this drastic drop in production.
The exact quantity and type of stocks of course varies from country to country and general statements are difficult to make. The figures and sources are only an order of magnitude.
Leaf, A. (1986): Food and Nutrition in the Aftermath of Nuclear War. The Medical Implications of Nuclear War.
https://www.ncbi.nlm.nih.gov/books/NBK219173/
Quote: “World food reserves, as measured by total cereal stores at any given time, are frighteningly small should production fail. They have amounted in recent years to about 2 months' supply of cereals at present consumption rates.1 In the United States food stores would feed the population for about a year.2 Portions of the stores, however, would be destroyed by blast or fire or would be contaminated by radioactivity.3, 4 Crops in the field would be damaged to an unpredictable extent.4,5”
Brown, L.R. (2009): Could Food Shortages Bring Down Civilizations? Scientific American Magazine Vol. 300 (5)
https://www.scientificamerican.com/article/civilization-food-shortages/
Quote: “In six of the past nine years world grain production has fallen short of consumption, forcing a steady drawdown in stocks. When the 2008 harvest began, world carryover stocks of grain (the amount in the bin when the new harvest begins) were at 62 days of consumption, a near record low. In response, world grain prices in the spring and summer of last year climbed to the highest level ever.”
– Today there are two main conflicts that scientists think about when making calculations of nuclear winter: a nuclear war between India and Pakistan and one between the US and Russia.
In addition to the known states that have nuclear weapons, there are also Israel and North Korea. Israel neither denies nor confirms the possession of nuclear weapons, but it is assumed that Israel possesses around 90 warheads. North Korea's nuclear weapons program, on the other hand, is known (e.g. through tests), but is so obscure that it can only be estimated (30 warheads).
#SIPRI (2023): 7. World nuclear forces. Yearbook 2023
https://www.sipri.org/sites/default/files/YB23%2007%20WNF.pdf
Quote: “Israel continues to maintain its long-standing policy of nuclear ambiguity: it neither officially confirms nor denies that it possesses nuclear weapons.2 This lack of transparency means that there is significant uncertainty about the size of Israel’s nuclear arsenal and the yields and characteristics of its weapons.3 The estimate here is largely based on calculations of Israel’s inventory of weapon-grade plutonium (see section X) and the number of operational nuclear-capable delivery systems. The locations of the storage sites for the warheads, which are thought to be stored partially unassembled, are unknown.
(...)
The Democratic People’s Republic of Korea (DPRK, or North Korea)
maintains an active but highly opaque nuclear weapon programme. SIPRI
estimates that, as of January 2023, North Korea possessed around 30 nuclear
weapons (see table 7.9, end of section), but that it probably possessed sufficient
fissile material for an approximate total of 50–70 nuclear devices, depending
on warhead design.”
– The most likely smallish nuclear exchange would be fought today between India and Pakistan, with relatively low yield weapons. Even in a pretty mild nuclear war like this, the immediate explosions would kill around 27 million people, which is horrible enough. In just a few hours, more people would die than in all of World War 1.
This scenario (“5 Tg”) assumes a detonation of 100 nuclear bombs of 15 kt each in the urban zones of India an Pakistan. 15kt corresponds to one atomic bomb that destroyed Hiroshima.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
(table: https://www.nature.com/articles/s43016-022-00573-0/tables/1)
The weapons arsenals of India and Pakistan have been growing for decades and each numbered around 160 to 170 warheads in 2023. The number is likely to increase in the coming years.
Both countries have fought several wars against each other and skirmishes occur time and again. The risk of a nuclear escalation seems to be a possibility.
#FAS (2023) Federation of American Scientists. Status Of World Nuclear Forces.
#Warden, C. (2022): Hiding in Plain Sight: India and Pakistan’s Global Environmental Threat. Center for Arms Control and Non-Proliferation
https://armscontrolcenter.org/hiding-in-plain-sight-india-and-pakistans-global-environmental-threat/
Quote: “While all tense relationships between nuclear powers are concerning, the relationship between India and Pakistan stands out since the two countries have already engaged in multiple conventional armed conflicts following Partition in 1947.
(...)
The decades of conflict between the two countries and frequent escalation make an India-Pakistan nuclear war an unsettling possibility. India’s capabilities in conventional warfare far outweigh Pakistan’s; India’s “Cold Start” military doctrine allows the Indian military to theoretically mobilize large numbers very quickly, meaning that India could potentially swiftly defeat Pakistan in a conventional war. As a result, Pakistan relies on an extreme nuclear doctrine to counteract this perceived imbalance. Russia’s lack of military success in Ukraine, despite an even greater conventional advantage than India’s, has not changed the equation for Islamabad. Additionally, both India and Pakistan have both increased their nuclear arsenals in recent years.
Hans Kristensen, the current director of the Nuclear Information Project at the Federation of American Scientists, said, “when it comes down to nuclear weapons states that could end up in a nuclear clash against each other, India and Pakistan has for years been considered the most likely.””
– The ensuing fires would not cause a nuclear winter, but a mild ‘nuclear autumn’. But even this would disrupt the climate, and thereby global agriculture, enough to starve up to 250 million people worldwide.
The red lines show the calculated temperature and solar radiation curves of the "5 Tg" scenario. Over cropland (a), temperatures will be lower by a maximum of 2°C for a few years and then level off again to the initial value over the following years. The temperature over the oceans (b) is less affected. Less solar radiation (c) will reach the earth. However, compared to the other scenarios (lines with a different colour), the decrease is small.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
Based on the previous scenario (Toon, O.B. et al. (2007)), the study estimates the impacts of the “nuclear climate change” on food supply from crops, marine fishery and livestock production.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
Quote: “Nuclear war would primarily contaminate soil and water close to where nuclear weapons were used22. Soot disperses globally once it reaches the upper atmosphere; thus, our results are globally relevant regardless of the warring nations. Here, we focus on the climate disruption from nuclear war, which would impact global food production systems on land and in the oceans. So far, an integrated estimate of the impacts of the entire range of war scenarios on both land- and ocean-based food production is missing. We examine the impacts of six war scenarios, generating 5 Tg to 150 Tg of soot, on the food supply (Table 1). We use model simulations of major crops and wild-caught marine fish together with estimated changes in other food and livestock production to assess the impacts on global calorie supply.”
When calculating the number of people who starve to death in the second year, there are various assumptions, e.g. that trade between countries is stopped and whether and how the feed is used for feeding livestock or for food. We refer to the assumption that 50% of the feed is used for humans and 50% for the actual purpose, for livestock.
In the table, all countries are listed separately, but for reasons of simplicity we only show the end of the table here, which shows the total number (column “5 Tg”).
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Supplementary information. Nature Food Vol. 3
– Unfortunately India and Pakistan are in an arms race and have been increasing the number and power of warheads in their arsenal.
We have already described the increasing number of warheads above. In addition to the number of warheads, further development of the launcher systems and the infrastructure for producing warheads is of course also relevant. Details on the individual programs of the individual countries can be found in the following source.
#Kile, S.N. & Kristensen, H. M. (2017): Trends in World Nuclear Forces, 2017. SIPRI Fact Sheet
https://www.sipri.org/sites/default/files/2017-06/fs_1707_wnf.pdf
Quote: “India and Pakistan are expanding their military fissile material production capabilities on a scale that may lead to signifi cant increases in the size of their nuclear weapon inventories over the next decade.
(...)
The nuclear arsenals of the other nuclear weapon-possessing states are considerably smaller (see fi gure 3), but all are either developing or deploying new weapon systems or have announced their intention to do so. China has embarked on a long-term modernization programme focused on making qualitative improve ments to its nuclear forces rather than on signifi cantly increasing their size. India and Pakistan are both expanding their nuclear weapon stock piles as well as developing new land-, sea- and air-based missile delivery systems.”
#Toon, O. B. et al. (2019): Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. Science Advances, Vol. 5 (10)
– The next stage of escalation would be war with hundreds of nuclear weapons, the bombs and fires destroying many major population centers and killing over 100 million people. A war on this scale would cause a nuclear winter that would damage global agriculture enough to cut the available calories for humanity in half.Within a year the number of people that starve to death would be as high as 2 billion. One in four humans alive today.
The following source describes a scenario (“S1”) in which a total of around 250 nuclear weapons are used in a conflict. It discusses the political background and possible triggers, but also compares the arsenals of both states, how many of the launched weapons actually work and describes the global, climatic effects.
#Toon, O. B. et al. (2019): Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. Science Advances, Vol. 5 (10)
https://www.science.org/doi/10.1126/sciadv.aay5478#abstract
Quote: “Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people, and nuclear-ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years. Net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities.”
You can find those tables in the supplementary material of the sources: https://www.science.org/doi/suppl/10.1126/sciadv.aay5478/suppl_file/aay5478_sm.pdf
This scenario assumes 250 nuclear weapons that have each several times the explosive power of the Hiroshima atomic bomb (15 kt), namely (100 kt) each.
In this case, there could be almost 130 million direct deaths and more than 2 billion people starving to death in the second year.
In the table, all countries are listed separately, but for reasons of simplicity we only show the end of the table here, which shows the total number (column “37 Tg”).
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Supplementary information. Nature Food Vol. 3
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
(table: https://www.nature.com/articles/s43016-022-00573-0/tables/1)
In this 37 Tg scenario, calculations show that the available calories from crops and marine decrease by almost 50% (fig. 2c, purple graph)
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
– The worst-case scenario is a full scale global war between NATO nations and Russia – or China, which also continues to build its nuclear arsenal. In a war between a former, future and current superpower, thousands of nuclear weapons could be detonated.
We have simplified things here for the purpose of visualization. The scenario (called “SORT” in the following source) is a bit more complex.
#Toon, O. B. et al. (2008): Environmental consequences of nuclear war. Physics Today, Vol. 61 (12)
https://pubs.aip.org/physicstoday/article/61/12/37/393240/Environmental-consequences-of-nuclear-warA
Quote: ”The Strategic Offensive Reductions Treaty (SORT) of 2002 calls for the US and Russia each to limit their operationally deployed warheads to 1700–2200 by December 2012.
(...)
In the SORT conflict, we assume that Russia targets 1000 weapons on the US and 200 warheads each on France, Germany, India, Japan, Pakistan, and the UK. We assume the US targets 1100 weapons each on China and Russia. We do not consider the 1000 weapons held in the UK, China, France, Israel, India, Pakistan, and possibly North Korea.”
In 2023, it was estimated that there were nearly 10,000 potentially usable nuclear warheads in military stockpiles spread across nine states while around 4,000 each belong to the USA and Russia.
#SIPRI (2023): Yearbook 2023: Armaments, Disarmament and International Security
Quote: “At the start of 2023, nine states—the United States, the Russian Federation, the United Kingdom, France, China, India, Pakistan, the Democratic People’s Republic of Korea (DPRK, or North Korea) and Israel—together possessed approximately 12 512 nuclear weapons, of which 9576 were considered to be potentially operationally available. An estimated 3844 of these warheads were deployed with operational forces (see table 7.1), including about 2000 that were kept in a state of high operational alert—the same number as the previous year. Overall, the number of nuclear warheads in the world continues to decline. However, this is primarily due to the USA and Russia dismantling retired warheads.”
#FAS (2023) Federation of American Scientists. Status Of World Nuclear Forces.
– In a scenario with around 4400 nuclear weapons, 360 million people would perish right away. We have no other event to even compare the death and destruction to.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
(table: https://www.nature.com/articles/s43016-022-00573-0/tables/1)
In the table, all countries are listed separately, but for reasons of simplicity we only show the end of the table here, which shows the total number (column “150 tg”). More than 5 billion people would die from starvation.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Supplementary information. Nature Food Vol. 3
– The nuclear winter that follows such an apocalyptic war would tank human calorie production by as much as 90%.
Figure 5 b shows the temperature change of different scenarios over the years. The mentioned "150 Tg" scenario (green) shows temperature decreases of up to minus 11°C in the first years.
In comparison, the purple bar shows the temperature difference (compared to today) during the height of the Last Glacial Maximum about 20,000 years ago. The lowest temperatures even fall below the lowest temperatures of this ice age. “Nuclear Winter” therefore seems a fitting metaphor.
However, these temperatures are already reached by other scenarios (27.3 Tg, black). This scenario can already be reached in a regional conflict between India and Pakistan in which 250 nuclear weapons of 50 kt each are detonated.
#Toon, O. B. et al. (2019): Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. Science Advances, Vol. 5 (10)
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
Quote: “Using climate, crop and fishery models (Methods), we calculate calorie production for different food groups, for each year after a range of six different stratospheric soot injections. The climatic impacts would last for about a decade but would peak in the first few years (Fig. 1).
(...)
Global average calorie production from the crops we simulated decreased 7% in years 1–5 after the war even under the smallest, 5 Tg soot scenario (Fig. 2a; comparable to previous multi-model results14, Supplementary Fig. 2) and up to 50% under the 47 Tg scenario. In the 150 Tg soot case, global average calorie production from crops would decrease by around 90% 3–4 years after the nuclear war. The changes would induce a catastrophic disruption of global food markets, as even a 7% global yield decline compared with the control simulation would exceed the largest anomaly ever recorded since the beginning of Food and Agricultural Organization (FAO) observational records in 196114.
(...)
– Not only would almost all of our agriculture take an immediate and deadly hit, the climate would take at least a decade to recover.
#Toon, O. B. et al. (2019): Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. Science Advances, Vol. 5 (10)
https://www.science.org/doi/10.1126/sciadv.aay5478#abstract
The examples of precipitation and temperature change show that in the full-scale scenario (150 days, green graph), the values only roughly return to the normal level after 10, 11, 12 years and even then take a few more years to return to the initial value.
– Globally about 5 billion would perish within two years from starvation.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
(table: https://www.nature.com/articles/s43016-022-00573-0/tables/1)
In the table, all countries are listed separately, but for reasons of simplicity we only show the end of the table here, which shows the total number (column “150 tg”). More than 5 billion people would die from starvation.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Supplementary information. Nature Food Vol. 3
– So a few countries like Australia, New Zealand, and Argentina may be able to endure for a bunch of different reasons.
As you can see, in all scenarios (from a regional conflict to a full-scale one) and in all conditions (e.g. crop used only for humans or partly for livestock), Argentina and Australia are countries that have enough calories available to sustain their normal activities.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
– Their nuclear winter would be milder, they have a lot of livestock that would not be as affected as crops. So they would probably stop exporting food and focus on keeping their own people alive – assuming they aren’t invaded for their food by other starving nations.
Even though the southern hemisphere would be massively affected by a full-scale war, the consequences would not be quite as dramatic as in the northern hemisphere, as we have already explained above with examples of temperature changes and growing seasons.
#Xia, L. et al (2022): Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nature Food Vol. 3
https://www.nature.com/articles/s43016-022-00573-0#Abs1
Quote: “Under the 150 Tg scenario, most nations would have calorie intake lower than resting energy expenditure29. One exception is Australia. After we turn off international trade, wheat contributes almost 50% of the calorie intake in Australia, and production of rice, maize and soybean in Australia are less than 1% that of wheat23,24. Therefore, the wheat response to simulated nuclear wars largely determines calorie intake in Australia. Because spring wheat is used to represent wheat, and simulated spring wheat there shows increasing or small reductions under nuclear war scenarios in which more favourable temperatures occur for food production, the calorie intake in Australia is more than other nations. However, this analysis is limited by the FAO data, which are collected at national levels. Within each nation, particularly large ones, there may be large regional inequities driven by infrastructure limitations, economic structures and government policies. New Zealand would also experience smaller impacts than other countries. But if this scenario should actually take place, Australia and New Zealand would probably see an influx of refugees from Asia and other countries experiencing food insecurity.”
Robock, A. et al. (2023): Opinion: How fear of nuclear winter has helped save the world, so far. Atmospheric Chemistry and Physics, Vol. 23
https://acp.copernicus.org/articles/23/6691/2023/acp-23-6691-2023.pdf
Quote: “The results in Figs. 3 and 4 depend on the assumptions made in our study. You might survive a nuclear war fought in the Northern Hemisphere by living in Argentina, Australia, or New Zealand. Indeed, because we assumed that international trade in food would collapse after a nuclear war, and these are all large food exporting nations, there would be enough locally produced food to feed their current populations.”
Quote from one of the experts (Dr. Lili Xia) we contacted and author of cited studies:
"Countries show better situation in the paper are a result of mixed reasons, and each country is different. The reasons could be (1) exporting countries after close international trade have more food available; (2) countries with livestock feeding primarily by pasture. pasture shows less reduction than crops; (3) less temperature reduction."