Life on Earth depends on a stable climate. Both the biosphere and our global society are calibrated to a narrow band of habitability. The global temperature is governed by a lot of interacting systems, but it mostly boils down to how much energy from the Sun reaches the planet’s surface and how much of incoming energy stays in the Earth’s system. Humans mess with this system by trapping more energy here, by releasing more carbon dioxide than the Earth’s system can handle. However, there are also two other, more hypothetical ways humans might impact the climate, which instead mess with the amount of incoming radiation: 1) intentional stratospheric aerosol injection to combat climate change and 2) the release of massive amounts of soot as the consequence of a nuclear war. All three are linked by their influence on the global climate, and in this post I want to discuss their potential interactions and why we should keep the others in mind when we talk about any of them.

Three dials in the same system

Climate change

If you don’t manipulate the Earth system, the amount of incoming radiation is pretty much fixed, as the sun has a fairly stable output of energy (at least on human timescales). The main variable that changes the temperature on Earth is how much energy remains on it, which in turn is strongly balanced by the amount of carbon dioxide in the atmosphere. Other gases and processes also matter a lot for the temperature (e.g. water vapor, albedo, or the tilt of the Earth). But here I want to focus mostly on carbon dioxide, because it is the one most easily manipulated by humanity. Carbon dioxide exists in a delicate balance when Earth is left undisturbed. New carbon dioxide is emitted from volcanoes and existing carbon dioxide is removed when rock weathers. The rate of rock weathering in turn is influenced by how warm and moist it is, which is also influenced by carbon dioxide concentrations. This means you have a self-regulating thermostat for the global temperature. However, since industrialization humanity has been messing with this thermostat. We have been adding much, much more carbon dioxide than can be removed quickly by weathering. This means we put the system out of equilibrium, we trap more energy on the planet and thus warm it (1). The timescale we are talking about here is decades to centuries. Thankfully, the Earth system is large enough to compensate for at least some of our messing around.

One great paper that tries to explore the most extreme consequences of our messing around is by Kemp et al. (2022). In it Kemp and co-authors try to shine a light on what research has already been done on the most extreme facets of climate change and how it might interact with other catastrophes. They highlight that our knowledge about the most extreme scenarios is scarce, especially when we want to discuss how a world which is out of balance due to climate change might react if this interacts with other anthropogenic impacts like a nuclear war or stratospheric aerosol injection.

Nuclear winter

Nuclear winter is a hypothesized consequence of a nuclear war, where soot particles block out sunlight and cool the planet. This process is explained in detail in Coupe et al. (2019), who conducted a big nuclear winter modeling study. The idea is that the explosion of nuclear weapons ignites whole cities all at once. These fiercely burning cities get so hot that they create a massive firestorm. A firestorm creates so much heat that air rises very quickly above it, like in a chimney, and new, oxygen-rich air is sucked in from the surroundings, creating an even hotter fire. This can create such a strong effect that the soot from the fire is sucked up into the upper atmosphere. Once there the black soot particles heat up and create warmer air around themselves, which carries them upwards, a process called self-lofting. Once they are high up in the atmosphere, they are distributed globally and block out the sunlight. We know this is possible in principle because big forest fires are able to loft smaller amounts of soot up into the stratosphere regularly. The main tricky question around this is: how burnable are cities actually? Depending on this the likelihood of a firestorm changes and how much soot is produced. As we haven’t been torching down whole cities all at once since the middle of the last century, there is little data to base this on, and the modelling studies disagree widely. If you want to learn more about these debates, see here for a detailed discussion of the state of nuclear winter research and here for a history of nuclear winter research and why we know so little about it.

The climate impact would be quite severe. The global land surface temperature could drop by up to almost 10°C after only two years in the most extreme simulations (2) (for land surfaces) and even for much smaller nuclear wars as discussed in Xia et al. (2022) temperatures in cropland areas could drop 4-6°C Thankfully, it only takes about 10 years to get back to normal. The tricky thing is to survive that long, as it would strongly impact food systems.

Stratospheric aerosol injection

Stratospheric aerosol injection involves deliberately releasing aerosols into the stratosphere to reduce incoming sunlight. Unlike nuclear winter scenarios where soot particles absorb and block light, this approach typically uses sulfate particles that scatter sunlight. The process would require aircraft to continuously disperse these particles at high altitude, since they are naturally removed from the atmosphere over time. This would have to be done on both hemispheres at once.

This geoengineering approach remains deeply controversial. It represents a massive intervention in Earth’s climate system with potentially unpredictable consequences. However, it also offers a potential emergency response if conventional climate mitigation efforts prove insufficient and might help avoid triggering tipping points. So far, there have only been a few smaller experiments, but it seems likely that the resources needed to employ it on a larger scale are within the power of many larger nation states. As it is not clear how much sulfate we would need exactly, a slow ramp up period would be sensible to make sure that we do not overdo it.

One paper that dives deeper into the consequences is by Tang and Kemp (2021). They argue that these consequences can happen directly from the way the radiation management is deployed, but also by interacting with other hazards. They frame this as it being a latent risk, meaning a risk that lies dormant, but can later be triggered. This is what is often called the “termination shock”, a sudden warming after the dispersion of sulfate is stopped, especially if carbon dioxide emissions kept on rising while the sulfate was in the atmosphere. Additionally, the sulfate emissions could have negative consequences on ecology mainly by shifting weather patterns in hard to predict ways.

Stratospheric aerosol injection also requires near-perfect international coordination for decades, or possibly even centuries, to balance out who profits and who loses from their deployment. This would likely be extremely difficult to pull off, due to differing regional impacts and deciding who will pay for the program. Additionally, the infrastructure and planes to implement the program would be an easy target for hostile actors.

How these processes potentially interact

We see that each of the three processes has a lot of destructive potential on its own, but here I want to highlight the dangers and consequences we might face if they interact. They all influence the global temperature and weather patterns, but partly push it into different directions.

Stratospheric aerosol injections + nuclear winter

Tang and Kemp explicitly discuss this potential interaction. Both stratospheric aerosol injection and nuclear winter push the climate to a cooler state. This means if a nuclear war happens, while sulfate aerosols are emitted, this could add together and lead to an additional cooling. Also, there does not exist any research that looks at how soot and sulfate might interact in the atmosphere.

The nuclear war, which would have to happen before the nuclear winter, would also lead to additional disruption, especially if high-altitude electromagnetic pulses were used, which would destroy electrical equipment on continental scale. If this would affect the nation(s) which are dispersing the sulfates in the atmosphere, this would lead to an instant stop of dispersion and thus to a termination shock, right after the climate had recovered from the nuclear winter. It seems likely that once the program is disrupted, it would be difficult to restart it again, due to the general chaos and disruption. This means stratospheric aerosol injection would make nuclear war more dangerous, and vice versa. Though if you manage to maintain it, it could help to create a smooth transition in and out of nuclear winter.

This scenario of a global catastrophe like nuclear war disabling the ability to continue with solar radiation management is also mapped out in detail in Baum, Maher, and Haqq-Misra (2013). They even go so far to suggest that such a scenario might be a potential way for human extinction, because such a massive climate shift would be hard to muddle through and even if you make it, you would live in a world which is ravaged by high global warming.

Theoretically, this also implies that you could gradually phase out the sulfate emissions to counter global cooling. Though this would likely be very difficult to time it just right, especially in a world that has just gone through a nuclear war, which would make global cooperation hard to come by. However, the research I could find that looks into the costs of stratospheric aerosol injections (e.g. Smith (2020)) usually comes up with estimates around 10-20 billion US dollars per year and per degree Celsius of warming avoided. As this is relatively cheap in comparison to many other things that states do, it might be possible to pull this off by a single country, avoiding the whole coordination problem after nuclear war.

All this means that stratospheric aerosol injection seems like a very high risk, high reward strategy if you also consider the different hazards we phase.

Climate change + nuclear winter

Climate change influences the state of the Earth system and thus the baseline from which a nuclear winter would happen. This is explored in Jehn (2023) (Disclaimer: This is one of my own papers). The paper reviews how crossing planetary boundaries might affect nuclear winter scenarios. The analysis is mostly pessimistic, though climate change could potentially offer one benefit: if nuclear winter occurs in an already warmed world, the temperature drop might be easier to manage. This is because our climate adaptation measures—both in infrastructure and ecosystems—typically lag behind actual warming, creating a buffer. However, this remains highly speculative since no climate models have examined this combined scenario. It is also plausible that a nuclear winter would hit even harder in a world that has prepared for heat, not cold.

Another paper I want to highlight here is by Egeland (2025). This paper tries to entangle how climate change and nuclear threats intersect. It highlights a number of interactions:

• Many nuclear weapon sites are in areas that will be highly affected by climate change and will have to be moved, which is costly and often politically difficult.
• Melting Arctic sea ice will make it harder for Russian submarines to hide, decreasing deterrence and thus making the nuclear world less stable.
• Climate change increases conflict in general and thus also the danger of nuclear weapon usage.
• Globally, we are seeing increased defense spending. This will likely increase carbon emissions, as the military is already responsible for around 5% of global carbon emissions.
• Defense spending is often prioritized over spending for avoiding climate change.
• Nuclear weapons are a cheaper way to project force than traditional military assets. This means if climate change decreases economic growth, there will be an incentive to focus more on nuclear weapons to save money.
• Climate change will likely lead to lots of migration, as people flee uninhabitable places. This will lead to more destabilization.

All of this points to a self-reinforcing spiral: climate change makes the world less stable, a less stable world focuses more on defense, more defense spending means less focus on avoiding climate change. This in turn implies more climate change leads to a higher chance of a nuclear war and thus a nuclear winter.

Climate change + stratospheric aerosol injection

Stratospheric aerosol injection is only a partial fix for climate change. As discussed above and in Tang and Kemp (2021), it does not solve the underlying problem of elevated carbon dioxide emissions, it just mitigates some of the effects. This means other negative effects of elevated carbon emissions, like ocean acidification, will just continue and destroy ecosystems. Besides this and the already discussed problem of the termination shock, there are also ethical problems when using stratospheric aerosol injection:

• Stratospheric aerosol injection can be used as an excuse to delay ending carbon emissions. Much of the current climate change action is driven by the fact that there is no alternative to solving climate change. Stratospheric aerosol injection isn’t one, but it can be perceived as such and therefore potentially decrease climate action.
• Also, stratospheric aerosol injection leads to thorny moral issues. It seems possible that the sulfate in the atmosphere might change precipitation patterns. This would often hit countries which haven’t been large greenhouse gas emitters historically, like India. While India will also be hit by climate change, they would be understandably pissed if someone turned off their rain season by injecting sulfate in the upper atmosphere.
• The nation(s) that control the program might have an incentive to shape the climate in a way that is preferable to them, such as trying to preferentially cool some regions compared to others.

All three at once

I think it is safe to say that a scenario of high emission climate change, nuclear winter and a termination shock, due to interrupted stratospheric aerosol emissions would be catastrophic. As far as I know, there is no piece of research that looks into the question of what these three things together might lead to. But let’s imagine a scenario:

It is 2075. Humanity has been engaged in stratospheric aerosol injection for some decades now. This is mostly done by China, because they have the resources to do so, and lots to lose by more warming. Unfortunately, this has led to a slow down of climate action and emissions have continued. While the sulfate has managed to limit warming to around 1°C, it has also led to an ever weaker rain season in many parts of Asia. Relationships between China and India (as well as many other states that now don’t have a rain season anymore) have gotten more and more tense over this. Finally, India decides that enough is enough and starts shooting down the Chinese planes that bring the sulfate into the stratosphere. This is seen as an act of war by China and they start attacking Indian air defenses. The conflict quickly spirals to a nuclear conflict, as both states see it as a struggle for their future. As predicted by many wargaming scenarios, the nuclear conflict cannot be contained, and all other nuclear weapon states are drawn into the exchange, resulting in an all-out nuclear war, which devastates the Northern Hemisphere. Temperatures quickly drop globally. As much of the world economy is destroyed and the rest is massively disrupted, there is little coordination on how to react to the coming nuclear winter, resulting in even more deaths due to famine. As the skies slowly clear again, the termination shock kicks in and the world is catapulted from freezing temperatures to +3.5°C warming in just 10 years.

I leave it as an exercise to the reader to estimate how much of our global society would remain after this chain of events.

Conclusion

I think all this highlights that we know very little about potential hazard interaction on global scales, but what we know all points in the direction that we should put massive efforts into making sure none of these things come true. Climate action is the most important thing, because it allows us to avoid the others. If climate change does not go much above 2°C (or preferably even less) we don’t need stratospheric aerosol injection, as these temperatures are likely still manageable. Also, if we rein in climate impacts, we won’t have as many global conflicts, thus reducing the likelihood of nuclear war. The safest path is emissions reduction, there are no easy fixes. This would also help avoid potential catastrophic interactions we haven’t even foreseen yet.

We should also keep in mind here the different timescales. Climate change is pretty much baked in for centuries. This means for this whole time period, we have to make sure that we don’t trigger the shorter time frame catastrophes of termination shock or nuclear winter.

Pretty much all of the papers I cited here also emphasize that we need more system-level analysis, not just individual hazards. Our world is very complex, especially if you want to consider natural and anthropogenic systems at once. This means considerable research is needed, but preferably on a more holistic level, trying to assess the whole system, not just facets. This is hard, but if we want to really understand the risks that we are facing, I see no way around it.

Endnotes

(1) If you want to understand this in more detail, Ruddiman (2013) is a good explainer and quite comprehensive.

(2) A recent report by National Academies of Sciences, Engineering, and Medicine (2025) questions if such a stark temperature drop could be reached with present day arsenals, but keeping it in here to illustrate the potentially very large effects.

References

• Baum, Seth D., Timothy M. Maher, and Jacob Haqq-Misra. 2013. “Double Catastrophe: Intermittent Stratospheric Geoengineering Induced by Societal Collapse.” Environment Systems & Decisions 33(1):168–80. doi:10.1007/s10669-012-9429-y.
• Coupe, Joshua, Charles G. Bardeen, Alan Robock, and Owen B. Toon. 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.” Journal of Geophysical Research: Atmospheres 124(15):8522–43. doi:10.1029/2019JD030509.
• Egeland, Kjølv. 2025. “Disentangling the Nexus of Nuclear Weapons and Climate Change—A Research Agenda.” International Studies Review 27(1):viaf003. doi:10.1093/isr/viaf003.
• Jehn, Florian Ulrich. 2023. “Anthropocene Under Dark Skies: The Compounding Effects of Nuclear Winter and Overstepped Planetary Boundaries.” Pp. 119–32 in Intersections, Reinforcements, Cascades: Proceedings of the 2023 Stanford Existential Risks Conference. The Stanford Existential Risks Initiative.
• Kemp, Luke, Chi Xu, Joanna Depledge, Kristie L. Ebi, Goodwin Gibbins, Timothy A. Kohler, Johan Rockström, Marten Scheffer, Hans Joachim Schellnhuber, Will Steffen, and Timothy M. Lenton. 2022. “Climate Endgame: Exploring Catastrophic Climate Change Scenarios.” Proceedings of the National Academy of Sciences 119(34):e2108146119. doi:10.1073/pnas.2108146119.
• National Academies of Sciences, Engineering, and Medicine. 2025. Potential Environmental Effects of Nuclear War. Washington, D.C.: National Academies Press.
• Ruddiman, William. 2013. Earth’s Climate: Past and Future. New York: WH Freeman.
• Smith, Wake. 2020. “The Cost of Stratospheric Aerosol Injection through 2100.” Environmental Research Letters 15(11):114004. doi:10.1088/1748-9326/aba7e7.
• Tang, Aaron, and Luke Kemp. 2021. “A Fate Worse Than Warming? Stratospheric Aerosol Injection and Global Catastrophic Risk.” Frontiers in Climate 3.
• Xia, Lili, Alan Robock, Kim Scherrer, Cheryl S. Harrison, Benjamin Leon Bodirsky, Isabelle Weindl, Jonas Jägermeyr, Charles G. Bardeen, Owen B. Toon, and Ryan Heneghan. 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 1–11. doi:10.1038/s43016-022-00573-0.