Discover more from Existential Crunch
Anthropocene under dark skies
The compounding effects of nuclear winter and overstepped planetary boundaries
I want to try something different with this post here. The post is actually a conference paper for the Stanford Existential Risk Conference in April. I publish it both here and as a preprint to test if I can get more feedback for it this way. So, if you want to share your thoughts about this text, please do so, either in the comments here or by contacting me directly (e.g. via Mastodon). The manuscript will change over time, as I address feedback. If you want to make sure you read the most recent version you should check out the preprint on Zenodo.
The analysis of global catastrophic events often occurs in isolation, simplifying their study. In reality, risks cascade and interact. This is a fact that is all too familiar due to COVID-19. Therefore, it is essential to consider how global risks interact. This investigation explores the interplay between nuclear winter and planetary boundaries. It may seem reasonable to assume that respecting planetary boundaries, which ensure a safe planetary operating space, before a nuclear war is always preferable. However, that does not always seem to be the case. For instance, increasing nitrogen emissions presently could act as a nutrient buffer during nuclear winter. Contrastingly, mitigating climate change, means an even larger temperature drop in nuclear winter in comparison with pre-industrial times. Nevertheless, this explorative study also highlights planetary boundaries whose preservation contributes to human survival, both now and after nuclear war. The best example being biosphere integrity, as conserving it has no direct downsides and will make the Earth system more resilient to resist the shock of a nuclear winter.
1. Consequences of a nuclear war
Imagine a future after a full-scale nuclear war. An average person's life will dramatically change overnight. Many major cities could go up blazing in a firestorm, delivering large quantities of soot into the upper atmosphere (1, 2) and killing millions (3). This will change the climate globally (2). While there will be regions like Australia or New Zealand (4) which will still have bearable temperatures, other places like Eastern Europe or Canada will remain frozen for years (2). Under these circumstances, billions of people might starve (5).
But it does not have to be this way. Nuclear winter will affect everyone, but the biggest impact will be felt in many of the world's richest countries. The United States and Central Europe will be devastated, both by the direct impact of the nuclear weapons and the indirect effects of the changing climate (2). This gives a strong incentive for those nations to prepare and they have the resources to do so.
Imagine a different future. A future where humanity is prepared for the worst case. While there are technical solutions, which allow us to scale up resilient food sources like single cell proteins from natural gas (6) or seaweed (7), many of the problems we would have are linked to the way we are currently overusing the resources of our planet (8). For instance, if we can avoid the overuse of fisheries through regulations now, humanity will be left with more food in a nuclear winter (9). If we limit our footprint on the planet now, we will have more resources to cope with catastrophes.
It is likely that fisheries are not the only part where being more modest in our resource use today, would allow us extra resources in worst case scenarios. Many of the Earth’s systems are under considerable strain (8). Relieving this strain will allow humanity more leeway during catastrophic events. This study explores the interactions between nuclear winter and planetary boundaries to identify which boundaries we should focus on from an existential risks perspective. Nuclear winter can be seen as standing in here for other abrupt sunlight reduction scenarios (ASRSs) such as impact winter or volcanic winter, which refer to sun blocking due to asteroid/comet (bolide) impacts or large volcanic eruptions respectively. While there are differences between those three events, they are likely similar enough to also have comparable interactions with planetary boundaries.
2. Connecting planetary boundaries and nuclear winter
Planetary boundaries are a framework to evaluate the carrying capacity of the Earth System (8, 10). They highlight the parts of the earth system which ensure the habitability of Earth and how much strain they are under. This has shown that many important parts of the Earth System may be in a dangerous condition. Only three of the eight currently quantified planetary boundaries are in their safe operating space according to Holocene (last 12,0000 years) variation (8, 11). Especially, biodiversity and biogeochemical flows are beyond their safe limits (8). This means that they are taxed beyond their capacity and will degrade over time. The more those planetary boundaries are overstepped, the more strain will be put on the Earth's systems that allow humanity to exist. Agriculture in particular will be significantly impacted due to its reliance on boundaries such as freshwater, climate, and phosphorus and nitrogen cycles.
Agriculture will also be massively impacted by nuclear winter (5) or other ASRSs. Those are caused by particles in the upper atmosphere blocking out sunlight. This can happen via bolide impact (12), high-magnitude volcanic eruptions (13, 14), and nuclear war (2, 15). Given the lower rate of volcanic eruptions and bolide impact, nuclear war is the most likely candidate to lead to such a scenario. However, recent research also shows that volcanic eruptions might be more dangerous and likely than previously thought (16, 17). The blocking out of the sun will reduce incoming solar radiation, which will result in considerably lower temperatures and thus lower precipitation. This in turn will significantly decrease food production and make the current global system unviable. Recent research has highlighted that this could lead to global famine (5), though this could possibly be counteracted by implementation of resilient foods (18) like sugar from fiber (19) single cell proteins from hydrogen (20), or leaf protein concentrate (21). Still, it is very likely that a nuclear winter would bring a considerable strain on global food production.
Nuclear winter and planetary boundaries work on different time horizons. Overstepping planetary boundaries is a decade-long process that gets incrementally worse (8). Nuclear winter on the other hand is sudden and devastating in comparison (2). However, exploring their interaction is still valuable, as their difference in speed does not mean they cannot interact with each other. It merely means that every interaction identified, will get better or worse depending on how much humanity is able to stay clear of overstepping the planetary boundaries.
All this highlights that the main interaction of nuclear winter and planetary boundaries will most likely happen through agriculture. This fits into the classification of global catastrophic risks of Avin et al. (22), as this has also highlighted the food system as one of the elements of human society that is most at risk of global catastrophic events. Therefore, we need additional research that looks into possible problems in this area.
3. Other research looking into planetary boundaries and existential risks more broadly
I am not aware of any literature that is specifically looking into the interactions of nuclear winter and planetary boundaries. This is likely due to the fact that the existential risk studies field is relatively small, and has only really started in the last decade (23). Due to its novelty it also is somewhat separated from the traditional science around global problems, like planetary boundaries. In addition, planetary boundaries are still a relatively new concept as well (starting in 2009 (10)). Nuclear winter has been known as a problem since the 1980s (15), but did not get much public attention between the end of the Cold War and the invasion of Ukraine. Still, there is some research that is already exploring ideas with a similar spin like this study here.
Savitch et al. looked into how likely it is that exo-civilizations are creating their own version of an Anthroprocene and use simple models to find interactions between civilizations and their planet. Those models might be adaptable to planetary boundaries (24).
Geoengineering and termination shock in nuclear winter, are hinted at in Tang and Kemp (25).
Kemp et al in their climate endgame paper briefly touch on interactions of climate change and nuclear war (26).
Thomas Cernev has done research on global catastrophic risk and planetary boundaries in general, but it is more abstract than the direct comparison made here (27).
Scherrer et al. have shown that if we make sure to not overuse natural resources (fisheries as the example in their study), the planet would have a bigger buffer to use up during a nuclear winter (9).
Baum and Handoh established a framework (28) that tried to combine global catastrophic risks and planetary boundaries, but it seems like this has not been built upon in recent years.
4.1 Biosphere integrity
Biosphere integrity refers to the idea that changes in the biodiversity both locally and globally can have significant impacts on the functioning of the Earth system (8). These functions are important to humanity, as they offer ecosystem services like the cleaning of water or the pollination of plants. These services can only be maintained if enough of our environment can remain undisturbed (29). In the context of planetary boundaries this concept is subdivided into functional and genetic diversity (8). The former refers to the idea on how much the composition of the biosphere has changed since before the industrial revolution and the latter to the totality of the genetic diversity between all species and individuals. It remains unclear how much biosphere integrity is already damaged by human influence. However, it seems likely that every reduction in functional and genetic diversity is likely to be detrimental to the ability of the biosphere to cope with nuclear winter. Nuclear winter would have an outsized impact on the global biosphere. The biosphere has survived a number of very large volcanic eruptions (e.g. the Toba eruption (30)), which can also lead to a volcanic winter (31). However, the mechanisms of volcanic winters and nuclear winters are different. Volcanic winters are mainly caused by sulfates (13), while nuclear winters are caused by soot (2). This difference likely makes nuclear winters longer lasting (up to ten years) and therefore introduces a new challenge for the biosphere. The higher the biosphere integrity, the higher the chance that there will be no major disruption of the biosphere during a long nuclear winter and the easier the restoration of Earth will be when the climate returns to pre war states. Mitigating the impact of nuclear winter on humans by reducing starvation could spare some species that would otherwise be eaten by desperate humans or be unaffordable to save in zoos (32).
4.2 Climate Change
Climate change and nuclear winter can be seen as two sides of the same coin. Both are climatic changes driven by human actions, one making the planet too hot, the other making it too cold (33). They are even simulated using the same models, like the Community Earth System Model (CESM) (2, 34). Current predictions estimate an average warming between 2.1 and 3.9°C by 2100 due to climate change (35), while a nuclear winter caused by an all out nuclear war is estimated to cause a peak temperature drop of about 9 °C (2). This means even a largely out of control climate change, would not be enough to counteract the whole cooling effect of a nuclear winter. Still, global warming could dampen some of the effects of a nuclear winter. However, the crops will likely be optimized (either through location or genetic control) to the warmer climate (36), so a sudden temperature reduction would likely still be catastrophic. And this should not be seen as an argument that we should care less about climate change, as it might make us safer against another catastrophic event. The climate system is immensely complex and has many complex feedback loops and tipping points (37), and we have only limited research on higher temperatures (38, 39). Also, there simply is no research which looks at how exactly climate change and nuclear winter might interact. Still, we know that nuclear winter will likely influence large climatic patterns like El Niño (40), whose fluctuations are already getting more intense and frequent due to climate change (41). Therefore, even though climate change might make the cooling effect of nuclear winter easier to mitigate, betting on climate change to solve nuclear winter would be a very risky proposal with unforeseeable consequences. In addition, restoration after a nuclear winter is likely harder if this has to happen in a world under pressure of strong global warming and a world ravaged by climate change has likely a higher probability of nuclear war to start with.
4.3 Novel Entities
The term novel entities refers to the pollution of the environment with man made chemicals, which cause detrimental effects to humans and the environment (8). A well known example here is the usage of DDT in the 20th century, which almost led to the extinction of several species of birds of prey. As there is no background rate for such emissions, the planetary boundary for novel entities is defined as overstepped if globally more is produced than can be monitored, which is currently the case (11). The effects of most of the novel entities are chronic (11). This means that they will be detrimental to health during a nuclear winter as well, but not more so than they would have been otherwise. However, nuclear war itself will introduce additional novel entities into the environment, mainly caused by fallout (42) and the toxic chemicals produced by fires (43). Therefore, this would push concentrations further outside of the safe operating space. Still, due to the different nature of emission before and during a nuclear war, it is unclear how much it would help in nuclear winter to stay below this boundary now. Novel entities could be seen as an additional stress factor, not a major disruption in and of itself.
4.4 Stratospheric ozone depletion
The ozone layer protects the Earth’s surface from ultraviolet radiation. It was damaged by the release of ozone depleting substances (for example chlorofluorocarbons). After their ban by the Montreal Protocol the ozone layer started to regenerate and is now mostly intact again (10, 44). This leaves ozone depletion as one of the few planetary boundaries which is currently in the safe operating space. However, this would change significantly after a nuclear war. Even the earliest nuclear winter research hypothesized that the ozone layer would be negatively impacted (15) and recent research has estimated that the ozone losses will be rapid and global average losses could be as high as 75 % (45). The same effect, but to a lesser extent has also been established for smaller, regional nuclear wars (46). The main mechanism is reactions with nitrogen oxides, smoke and the general heating of the upper atmosphere (45). In the first few years the soot in the atmosphere will shield the surface from most of the incoming ultraviolet radiation. However, at the same time as soot is cleared from the atmosphere, the ultraviolet radiation rises and will reach UV index values of 35-45 (45) (not going outside is recommended for UV index > 11). Overall, it takes 12-15 years to return to pre war ozone levels and ultraviolet reductions. This means that it is important that we manage to keep the ozone layer intact, to not add to the devastating effect of the nuclear war. However, the effect of nuclear war on the ozone layer is likely in a different order of magnitude than problems with the ozone layer so far. It also shows that nuclear war will disrupt one of the few planetary boundaries we are currently managing to keep in safe operating space.
4.5 Atmospheric aerosol loading
This boundary is concerned with the totality of aerosols and their influence on human health and wellbeing. The aerosols also influence solar radiation by scattering it and hydrological cycles by altering cloud formation (10). Both are important for nuclear winter. The main mechanism that drives nuclear winter is the emission of soot by firestorms (2). Those emissions will contribute significantly to the atmospheric aerosol loading. An all out nuclear war may emit around 150 Tg of soot in a day to a week (2), while the global soot emissions per year are only around 4-22 Tg (47). It is not yet determined whether the planetary boundary for aerosol loading is overstepped now (8). However, there is evidence that the scattering of incoming solar radiation cools the Earth today by a small amount (48). Therefore, removing aerosols now will result in an overall warmer planet, which in turn will not cool as much due to nuclear winter. This raises the same problems as the interaction between climate change and nuclear winter (section 4.2): Is it better to have a warmer planet now, to also have a warmer planet during nuclear winter?
4.6 Ocean acidification
Oceans absorb carbon dioxide as a part of the global carbon cycle. The level of carbon dioxide dissolved in the upper ocean is in equilibrium with the atmosphere and depends strongly on the temperature of the water. As the levels of carbon dioxide rise in the atmosphere, so does the amount of carbon dioxide in the oceans. This in turn decreases the pH in the water. The largest effect of this is the disruption of the life cycles of all organisms who build shells from calcium carbonate. In addition, there is evidence that ocean acidification influences the availability of carbon, nitrogen and phosphorus in the oceans, with unclear effects on the ecosystem (49). Since the beginning of the industrial revolution this has led to a drop of around 0.1 in the global average of ocean pH (50). The most direct impact for humans will be the continuous decrease in the amount of catchable fish in the oceans, as the ecosystems get more and more out of balance and decline in productivity (51). Nuclear winter is predicted to increase the global pH by about 0.05. The effect is mainly driven by the decrease in sea surface temperature, which shifts the carbonate equilibrium in the water (52). While this might seem like a positive effect, modeling results show that it will rather worsen the problem. Marine species will have to adapt to a sharp increase in pH that will only take around a year to shift. However, as the ocean heats up again, as the soot in the atmosphere clears, the pH drops to its previous level, or even lower due to the killed plant matter decomposing. Such a rapid change in ocean chemistry would put a considerable strain on marine ecosystems. In addition, the cooling ocean during nuclear winter can dissolve more carbon dioxide, which in turn decreases the availability of carbonate even further (52), which means that the increase in pH does not help shell building organisms.
Overall, the interactions between ocean acidification and nuclear winter is likely to be negative. This implies that it is important to slow down ocean acidification now to leave ecosystems more room to adapt during a nuclear winter. This will also increase food availability today and after a nuclear war.
4.7 Biogeochemical flows
Biochemical flows mainly refer to the flows of nitrogen and phosphorus in the environment as two of the main nutrients (53). They are summarized under biogeochemical flows, as they are tightly connected. While both nitrogen and phosphorus are needed to sustain any ecosystem, they start to disrupt them as well once their levels change due to anthropogenic emissions (8, 10). The main negative effects for both phosphorus and nitrogen are dead zones and shifts in species composition. Dead zones refer to parts of the ocean or other water bodies which have been depleted of oxygen, after eutrophication shifted their species composition and abundance (e.g. algae blooms) (54). The main emission pathway for both nutrients are fertilizers, which have been overapplied for decades, especially in major food production countries like Germany (8).
There is no direct way that nuclear war would change biogeochemical flows. Still, there are possible interactions that have to be taken into account. Nuclear winter disrupts agriculture as it is practiced today by shifting climate zones globally and thus making agriculture very difficult if no adaptations are made (5). There are possibilities that allow us to still produce food, but those are under the assumption that enough nutrients remain available (18). This leads to the counterintuitive conclusion that overstepping the biogeochemical boundary now, might make humanity more resilient to nuclear winter, as more nutrients are available without needing additional fertilizer, which are likely hard to come by after a nuclear war. Around half of currently used fertilizers are synthetic and any stress on energy and supply chains will be felt. This does not mean that the nutrients available in the environment will allow production levels of today, but they will add a buffer, which will give additional time to set up production and trade for fertilizer in a post nuclear war world. Greater fertilizer production now would also mean larger amounts in storage, which would be helpful in a catastrophe (55).
4.8 Freshwater use
This boundary is concerned with the influence of humans on the global water cycle. It is in the safe operating space when there is still enough water to sustain ecosystem services (10). Currently this seems to be the case and the freshwater use planetary boundary is largely intact. However, future predicted water usage might bring it closer to its capacity (10).
Nuclear winter generally leads to less evapotranspiration and thus less precipitation (2). Therefore, the overall availability of water will decline, which means that full water storages now would give an additional buffer during nuclear winter. It is unclear how water usage will develop during nuclear winter. However, it might decline, as agriculture is one of the main water users and conventional agriculture will not be possible anymore in many places (5). However, it could also be helpful for nuclear winter to have used more water now, as this implies a larger water infrastructure, which could be helpful to allow a better water distribution. Overall, freshwater use now has likely not a very large impact on nuclear winter either way, though both positive and negative impacts are possible.
4.9 Land-system change
Land system change is driven mainly by the expansion of agriculture and the conversion of forests and grasslands to agricultural land (10). This threatens biodiversity and affects both the climate system in general and the hydrological cycle in particular. However, in relation to nuclear winter this boundary is likely to be of lower importance. While deforestation leads to fewer biomass available in nuclear winter, the global amount of trees is so large that this likely remains not an issue (56). Also, there might be a positive effect of clearing more land now, which would be also available in nuclear winter. The other way around is more important though. Nuclear winter will need a major shift in the way we produce food, which also includes relocating crops to warmer regions. In addition, the temperature drop in nuclear winter increases the area needed for crop production (18). Therefore, land-system change will likely be accelerated in a nuclear winter. Large parts of currently unused land might need to be converted to agriculture, for example for greenhouses (57). While those changes may be reverted once the climate returns to normal after a nuclear winter, this will still be a significant change in those systems, because they will need a considerable amount of time to be able to return to their pre war state.
5. Discussion and conclusion
Planetary boundaries are defined to highlight how we should treat the Earth to make it habitable for the long term. The included assumption here is that staying in the safe operating space is always better. This explorative study was a first exploration of how this assumption holds true when the planetary boundaries interact with existential risks. The insights gained here show that this assumption is often true, but not always. Overstepping planetary boundaries can both increase or decrease nuclear winter survivability, depending on which boundary has been broken (Figure 1). In addition, all boundaries are interconnected, and fixing one boundary may have unintended consequences for others.Overstepping the boundary on climate change results in an increase in temperature, which in itself has negative effects on the Earth system. However, this increase in temperature also means that during a nuclear winter, the planet would be cooled down from an elevated level, ultimately resulting in a lower peak cooling. This interaction might seem positive, but it remains unclear if it could lead to unforeseen consequences. Therefore, it is highly uncertain if this effect of climate change is positive. Overstepping the boundary on biogeochemical flows however might provide humanity with a nutrient buffer if overstepped, but it also has clear downsides today, like dead zones in the oceans. Therefore, it is essential to balance the present needs of human society with the long-term risks and benefits associated with overstepping planetary boundaries.
Figure 1: Visual summary and semi-quantitative assessment of the impact of overstepping planetary boundaries on the chances of survival for humanity after a nuclear war.
On the other hand, certain planetary boundaries, if overstepped, likely have only a negative impact on nuclear winter survivability. Ocean acidification, for example, is sensitive to the effects of a nuclear war and already under stress, which diminishes global food production today. Therefore, stopping ocean acidification has clear upsides. However, it is also the case that planetary boundaries are interconnected, and ocean acidification is mainly caused by elevated carbon dioxide levels. Bringing those back to pre industrial levels would stop ocean acidification, but also remove the temperature buffer provided by climate change.These findings highlight the importance of identifying and preserving boundaries that may provide upsides before and after a nuclear war. Stratospheric ozone depletion and biosphere integrity appear to be the most promising in this regard. But even here there are likely differences when it comes to costs and benefits. For example, the effect of nuclear winter on the ozone layer is quite strong and likely dwarfs any reconstruction of the ozone layer now. Changing the state of the earth relative to planetary boundaries is an enormous undertaking. Therefore, directed existential risk reduction activities are likely more cost-effective. However, if mitigating global catastrophes could be used to nudge existing funding in this space towards work on planetary boundaries that would be most synergistic with global catastrophes, this may be promising. Given the evidence presented here biosphere integrity is possibly the planetary boundary with the highest net positive effect on nuclear winter survivability. Preserving biosphere integrity now is clearly positive, it does not have obvious, strong interactions with other boundaries and it will provide humanity with a more stable Earth system overall, both now and in the nuclear winter.
Thanks to Ekaterina Ilin, Luke Kemp, Aron Mill and David Denkenberger for valuable comments to improve this manuscript.
1. N. Tarshish, D. M. Romps, Latent Heating Is Required for Firestorm Plumes to Reach the Stratosphere. Journal of Geophysical Research: Atmospheres 127, e2022JD036667 (2022).
2. J. Coupe, C. G. Bardeen, A. Robock, O. B. Toon, 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. Journal of Geophysical Research: Atmospheres 124, 8522–8543 (2019).
3. B. Habbick, Casualties in a nuclear war. Canadian journal of public health = Revue canadienne de sante publique 74 (1983).
4. M. Boyd, N. Wilson, Island refuges for surviving nuclear winter and other abrupt sunlight‐reducing catastrophes. Risk Analysis, risa.14072 (2022).
5. L. Xia, et al., Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection. Nat Food, 1–11 (2022).
6. J. B. García Martínez, et al., Methane Single Cell Protein: Potential to Secure a Global Protein Supply Against Catastrophic Food Shocks. Front. Bioeng. Biotechnol. 10, 906704 (2022).
7. F. U. Jehn, et al., Seaweed as a resilient food solution after a nuclear war (2023) https:/doi.org/10.5281/zenodo.7615254 (March 3, 2023).
8. W. Steffen, et al., Planetary boundaries: Guiding human development on a changing planet. Science 347, 1259855 (2015).
9. K. J. N. Scherrer, et al., Marine wild-capture fisheries after nuclear war. Proceedings of the National Academy of Sciences 117, 29748–29758 (2020).
10. J. Rockström, et al., Planetary Boundaries: Exploring the Safe Operating Space for Humanity. Ecology and Society 14 (2009).
11. L. Persson, et al., Outside the Safe Operating Space of the Planetary Boundary for Novel Entities. Environ. Sci. Technol. 56, 1510–1521 (2022).
12. C. R. Tabor, C. G. Bardeen, B. L. Otto-Bliesner, R. R. Garcia, O. B. Toon, Causes and Climatic Consequences of the Impact Winter at the Cretaceous-Paleogene Boundary. Geophysical Research Letters 47, e60121 (2020).
13. J. Luterbacher, C. Pfister, The year without a summer. Nature Geosci 8, 246–248 (2015).
14. J. Rougier, R. S. J. Sparks, K. V. Cashman, S. K. Brown, The global magnitude–frequency relationship for large explosive volcanic eruptions. Earth and Planetary Science Letters 482, 621–629 (2018).
15. R. P. Turco, O. B. Toon, T. P. Ackerman, J. B. Pollack, C. Sagan, Nuclear Winter: Global Consequences of Multiple Nuclear Explosions. Science 222, 1283–1292 (1983).
16. M. Cassidy, L. Mani, Huge volcanic eruptions: time to prepare. Nature 608, 469–471 (2022).
17. L. Mani, A. Tzachor, P. Cole, Global catastrophic risk from lower magnitude volcanic eruptions. Nat Commun 12, 4756 (2021).
18. M. Rivers, et al., “Food System Adaptation and Maintaining Trade Greatly Mitigate Global Famine in Abrupt Sunlight Reduction Scenarios” (2022) https:/doi.org/10.21203/rs.3.rs-1446444/v1.
19. J. Throup, et al., Rapid repurposing of pulp and paper mills, biorefineries, and breweries for lignocellulosic sugar production in global food catastrophes. Food and Bioproducts Processing 131, 22–39 (2022).
20. J. B. García Martínez, et al., Potential of microbial protein from hydrogen for preventing mass starvation in catastrophic scenarios. Sustainable Production and Consumption 25, 234–247 (2021).
21. J. M. Pearce, M. Khaksari, D. Denkenberger, Preliminary Automated Determination of Edibility of Alternative Foods: Non-Targeted Screening for Toxins in Red Maple Leaf Concentrate. Plants (Basel) 8, 110 (2019).
22. S. Avin, et al., Classifying global catastrophic risks. Futures 102, 20–26 (2018).
23. T. Ord, The Precipice: Existential Risk and the Future of Humanity (Hachette Books, 480 pp, 2020).
24. E. Savitch, et al., Triggering a Climate Change Dominated “Anthropocene”: Is It Common among Exocivilizations? AJ 162, 196 (2021).
25. A. Tang, L. Kemp, A Fate Worse Than Warming? Stratospheric Aerosol Injection and Global Catastrophic Risk. Frontiers in Climate 3 (2021).
26. L. Kemp, et al., Climate Endgame: Exploring catastrophic climate change scenarios. Proceedings of the National Academy of Sciences 119, e2108146119 (2022).
27. T. Cernev, “Global catastrophic risk and planetary boundaries: The relationship to global targets and disaster risk reduction” (2022) (August 25, 2022).
28. S. D. Baum, I. C. Handoh, Integrating the planetary boundaries and global catastrophic risk paradigms. Ecological Economics 107, 13–21 (2014).
29. A. Mohamed, et al., Biosphere functional integrity for people and Planet. 2022.06.24.497294 (2022).
30. C. A. Chesner, W. I. Rose, A. Deino, R. Drake, J. A. Westgate, Eruptive history of Earth’s largest Quaternary caldera (Toba, Indonesia) clarified. Geology 19, 200–203 (1991).
31. M. R. Rampino, Supereruptions as a Threat to Civilizations on Earth-like Planets. Icarus 156, 562–569 (2002).
32. D. C. Denkenberger, J. M. Pearce, Feeding everyone: Solving the food crisis in event of global catastrophes that kill crops or obscure the sun. Futures 72, 57–68 (2015).
33. A. B. Pittock, Climatic Catastrophes: The Local and Global Effects of Greenhouse Gases and Nuclear Winter in Natural and Man-Made Hazards, M. I. El-Sabh, T. S. Murty, Eds. (Springer Netherlands, 1988), pp. 621–633.
34. J. E. Kay, et al., The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability. Bulletin of the American Meteorological Society 96, 1333–1349 (2015).
35. P. R. Liu, A. E. Raftery, Country-based rate of emissions reductions should increase by 80% beyond nationally determined contributions to meet the 2 °C target. Commun Earth Environ 2, 1–10 (2021).
36. S. Minoli, J. Jägermeyr, S. Asseng, A. Urfels, C. Müller, Global crop yields can be lifted by timely adaptation of growing periods to climate change. Nature Communications 13 (2022).
37. D. I. Armstrong McKay, et al., Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science 377, eabn7950 (2022).
38. F. U. Jehn, M. Schneider, J. R. Wang, L. Kemp, L. Breuer, Betting on the best case: higher end warming is underrepresented in research. Environ. Res. Lett. 16, 084036 (2021).
39. F. U. Jehn, et al., Focus of the IPCC Assessment Reports Has Shifted to Lower Temperatures. Earth’s Future 10, e2022EF002876 (2022).
40. J. Coupe, et al., Nuclear Niño response observed in simulations of nuclear war scenarios. Commun Earth Environ 2, 1–11 (2021).
41. W. Cai, et al., Changing El Niño–Southern Oscillation in a warming climate. Nat Rev Earth Environ 2, 628–644 (2021).
42. J. Smith, T. Smith, Radiation injury and effects of early fallout. Br Med J (Clin Res Ed) 283, 844–846 (1981).
43. Y. Alarie, Toxicity of Fire Smoke. Critical Reviews in Toxicology 32, 259–289 (2002).
44. P. W. Barnes, et al., The success of the Montreal Protocol in mitigating interactive effects of stratospheric ozone depletion and climate change on the environment. Global Change Biology 27, 5681–5683 (2021).
45. C. G. Bardeen, et al., Extreme Ozone Loss Following Nuclear War Results in Enhanced Surface Ultraviolet Radiation. Journal of Geophysical Research: Atmospheres 126, e2021JD035079 (2021).
46. M. J. Mills, O. B. Toon, R. P. Turco, D. E. Kinnison, R. R. Garcia, Massive global ozone loss predicted following regional nuclear conflict. Proceedings of the National Academy of Sciences 105, 5307–5312 (2008).
47. T. C. Bond, et al., A technology-based global inventory of black and organic carbon emissions from combustion. Journal of Geophysical Research: Atmospheres 109 (2004).
48. N. Bellouin, et al., Bounding Global Aerosol Radiative Forcing of Climate Change. Reviews of Geophysics 58, e2019RG000660 (2020).
49. S. C. Doney, V. J. Fabry, R. A. Feely, J. A. Kleypas, Ocean Acidification: The Other CO 2 Problem. Annu. Rev. Mar. Sci. 1, 169–192 (2009).
50. Intergovernmental Panel on Climate Change, Ed., “Carbon and Other Biogeochemical Cycles” in Climate Change 2013 – The Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, (Cambridge University Press, 2014), pp. 465–570.
51. S. R. Cooley, S. C. Doney, Anticipating ocean acidification’s economic consequences for commercial fisheries. Environ. Res. Lett. 4, 024007 (2009).
52. N. S. Lovenduski, et al., The Potential Impact of Nuclear Conflict on Ocean Acidification. Geophysical Research Letters 47, e2019GL086246 (2020).
53. R. R. Leinfelder, J. Berndt, Humboldt-Universität zu Berlin, Eds., Science meets comics: proceedings of the Symposium on Communicating and Designing the Future of Food in the Antropocene (Ch.A. Bachmann Verlag, 2017).
54. D. W. Schindler, J. R. Vallentyne, The algal bowl: overfertilization of the world’s freshwaters and estuaries (Earthscan, 2008).
55. J. Mörsdorf, “Simulating potential yield if industry is disabled: Applying a generalized linear modelling approach to major food crops,” Justus-Liebig University, Gießen. (2021).
56. D. Denkenberger, J. Pearce, Feeding everyone no matter what: managing food security after global catastrophe (Academic Press, 2015).
57. K. A. Alvarado, A. Mill, J. M. Pearce, A. Vocaet, D. Denkenberger, Scaling of greenhouse crop production in low sunlight scenarios. Science of The Total Environment 707, 136012 (2020).