Florian U. Jehn

You might remember the warnings about the ozone hole, about skin cancer and eye damage on a huge scale. You don't hear about it anymore because it largely worked. Almost all ozone depleting substances have been phased out and the ozone layer is on track to recover. So we have proof that the world can solve a global pollution problem by treaty. Why not copy the Montreal Protocol for carbon? New post in my living literature review: https://existentialcrunch.substack.com/p/the-success-and-failure-of-the-montreal

#ClimateChange #MonrealProtocol #Policy

New paper is out!

We identified the worst crop shock every country experienced since 1961: the global average was −29%, with Botswana even losing 80% in a single year. Climate—especially drought—was the leading cause, although conflict is also a major contributor to crop failures. We can also see that the frequency of climate-driven shocks has doubled since the 1960s.

You can find the whole paper here: https://esd.copernicus.org/articles/17/151/2026/esd-17-151-2026.html

In the map below you can see the global distribution of the most severe shocks.

#Agriculture #CropFailure #Famine #Climate #Drought #conflict

New update post for my living literature review on societal collapse: https://existentialcrunch.substack.com/p/april-2026-updates
This means I go back to the old posts and add new papers I found, to make sure that everything stays as up to date as possible. Posts which got updated this time:

* What could go wrong? (https://existentialcrunch.substack.com/p/what-could-go-wrong): Added a summary of the future forecast by the United Kingdom Ministry of Defence and a paper by Jessica Graham et al. which discusses how the Swiss national risk assessment can inspire other countries like Australia.

* End time economics (https://existentialcrunch.substack.com/p/end-time-economics): Added a paper by Simon Blouin et al. that estimates how destruction of infrastructure leads to decreased industrial output, to better understand the potential effects of a nuclear war.

* Systemic risk and the polycrisis (https://existentialcrunch.substack.com/p/systemic-risk-and-the-polycrisis): Added a paper by Nicholas Studzinski et al. which discusses how systemic risk might be governed at an international level.

* Economic inequality and societal collapse (https://existentialcrunch.substack.com/p/economic-inequality-and-societal): Added a paper by Guido Alfani et al. which compares inequality in the Roman and Han Chinese empires.

* Trade collapse (https://existentialcrunch.substack.com/p/trade-collapse): Added a paper by Jasper Verschuur et al. that models the economic importance of all major global ports.

#Trade #Collapse #SystemicRisk #LivingLiteratureReview #Inequality

New post about the state of research around nuclear war and nuclear winter, with a focus on the food system.

This one's a bit different, as it was originally an invited contribution to the United Nations Independent Scientific Panel on the Effects of Nuclear War. I also wanted to share it publicly, because I think there just aren't that many summaries of the state of nuclear winter research out there.

It also discusses the most important gaps and unanswered research questions in the field. So, if you are interested in the topics in general or plan to work in the area, I think it could be an interesting read.

https://existentialcrunch.substack.com/p/nuclear-war-nuclear-winter-and-the

#NuclearWar #NuclearWinter #FoodSystem

Nuclear war is horrible and I hope it never happens. Yet, there are only a few countries that actually have nuclear weapons and the power to use them is concentrated in just a few individuals. This means the vast majority of the global population has no say on the question if nuclear weapons will be used.

However, due to a potential nuclear winter, which could follow a nuclear war, even countries on the other side of the globe could be directly affected by a nuclear war. This impact could be quite severe and as they have no direct measure to prevent it, these countries should think about how they would prepare. Also, many of the preparations that would be helpful for a nuclear winter would also help for the climatic consequences of large volcanic eruptions or asteroid impacts. So, they should be done anyway.

This is the gist of the argument I made in a new article in the Bulletin of the Atomic Scientists. You can read the full article here: https://thebulletin.org/2026/05/how-nuclear-war-would-impact-the-global-food-system-and-how-to-prepare-for-it/

#NuclearWinter #NuclearWar #FoodSystem #Trade

New preprint!

We reviewed global catastrophic risks: nuclear war, volcanic eruptions, asteroid impacts, cyberattacks, EMP, geomagnetic storms, and pandemics. Which places on Earth are most resilient?

The short answer: nowhere is safe from everything. Australia and New Zealand come closest, but even they have serious vulnerabilities (trade dependence or volcanic exposure).

The key finding is that resilience factors actively trade off against each other. Geographic isolation helps in pandemics but hurts during infrastructure collapse. A large industrial base helps produce emergency food but increases digital vulnerability.

What could help across scenarios: democratic governance, low inequality, decentralized systems, food self-sufficiency, and preparation. Most of these are policy choices, not geographic fate.

You can find the whole preprint here: https://eartharxiv.org/repository/view/12373/

#GlobalCatastrophicRisk #NuclearWar #Pandemic #GeomagneticStorm #Resilience

Next round of updates for my #LivingLiteratureReview. This means I go back to the old posts and add new papers I found, to make sure that everything stays as up to date as possible. Posts which got updated this time:
* Mapping out collapse research (https://existentialcrunch.substack.com/p/mapping-out-collapse-research): Added Goliath's curse and improved the overview figures of different collapse ideas.
* Famine's role in societal collapse (https://existentialcrunch.substack.com/p/famines-role-in-societal-collapse): Added my new paper about crop production shocks.
* Climate anomalies and societal collapse (https://existentialcrunch.substack.com/p/climate-anomalies-and-societal-collapse): Added a study about how extreme weather events were related to major battles in the Roman Empire.
* Economic inequality and societal collapse (https://existentialcrunch.substack.com/p/economic-inequality-and-societal): Added a paper that empirically explores how the onset of capitalism was pretty bad for many societies.

If you want to read about the updates in more detail, you can check out the update post: https://existentialcrunch.substack.com/p/december-2025-updates

#SocietalCollapse #Food #Climate #inequality

Had a great conversation with Samuel Arbesman on the podcast "The Orthogonal Bet" about all things collapse. If you are curious about the interdisciplinary nature of collapse studies, how it connects history to global catastrophic risk, and how societal resilience increases and decreases, check it out.

You can find it as podcast (https://pod.link/1796494444/episode/MGZlMTY2MmItZmVlOC00ZmE3LWJkNDUtMWE5MmEwYTVjMGU4?view=apps&sort=popularity) and on Youtube (https://www.youtube.com/watch?v=ayPkVL7wj4s&feature=youtu.be).

#collapse #resilience #GlobalCatastrophicRisk

One important factor to understanding the impact of global catastrophes is economics. How might agricultural prices rise? What are the general economic outlooks? In the next post in my living literature review I try to explore exactly this. The literature is scarce, but I still think we can learn some interesting things here.

https://existentialcrunch.substack.com/p/end-time-economics

#economics #NuclearWar #GlobalCatastrophicRisk

Who actually shapes global risk?

One common answer is to focus on individual apocalyptic actors, like terrorists aiming to end the world. But are these groups really what we should be on the lookout for most? Or should we not also consider institutional actors, like states, large militaries, or companies, who actually have the power and resources to meaningfully tip the global balance?

Find out more in post: https://existentialcrunch.substack.com/p/who-shapes-global-risk

#GlobalCatastrophicRisk #ExistentialRisk #Terrorism #Military

You are likely familiar with visions of doom.

When I look at the news, at blog posts, at conference abstracts, all everyone ever talks about is some shade of the world ending. And I would not even necessarily disagree with them. Many things are not developing in the right direction.

But I think something important gets lost if all we ever talk about are dystopian futures. Humans need something to strive for and in the past there were many grand narratives of how we could achieve a better world. But today? They seem to have disappeared. Not because they are not needed anymore, but because we have constrained what can even be talked about. Everything that could disrupt the status quo gets pushed to the sideline.

But how could we get started again? How could we talk about alternative ways to construct society?

This is the topic of my new blog post: https://existentialcrunch.substack.com/p/how-environmental-politics-lost-the

It is based on the great book Captured Futures by Maarten A. Hajer and Jeroen Oomen.

What are some positive visions that you would like people to talk more about? Feel free to leave a comment.

#ClimateChange #Environment #Politics #NetZero #Future