Florian Ulrich Jehn

Nuclear winter, caused by stratospheric soot injection after a nuclear conflict, would cause sustained cooling lasting years to over a decade. This cooling shifts precipitation from rain to snow and suppresses snowmelt, with largely unexplored consequences for snow storage and runoff. We force a global temperature-index snow model with climate simulations of three nuclear war scenarios (16, 47, and 150 Tg soot) and analyze runoff in six major river basins. Global snow storage peaks four to six years after the injection and remains slightly above control levels after 15 years. Three regional patterns emerge: new seasonal snowpacks, prolonged snow seasons, and multi-year accumulation at high latitudes. Larger snowpacks raise spring runoff peaks in the Rhine and Tigris-Euphrates, while high-latitude accumulation suppresses snowmelt elsewhere. These shifts would increase the potential for spring floods and prolonged low flows, affecting drinking water supply and irrigation.

The Atlantic Meridional Overturning Circulation (AMOC) functions as a critical climate tipping element, potentially capable of abrupt collapse under sustained anthropogenic forcing [1,2]. Current agricultural impact assessments predominantly focus on ongoing climate change trajectories [3,4], leaving the global food system's vulnerability to a climate shock like an AMOC collapse unquantified. Here we show the global agricultural and economic consequences of such a collapse. By coupling a 100-year climate anomaly [5] with global crop simulations, we identify a 5.3% structural decline in global wheat, maize, and rice production. We demonstrate that this biophysical penalty is geographically asymmetrical, triggering production collapses of 12% to 19% across highly concentrated Northern Hemisphere export hubs. Superimposing these reductions onto current global food trade networks reveals severe structural dietary deficits in import-dependent nations [6]. Finally, economic modeling indicates that if this protracted multi-breadbasket failure outpaces market adaptation, global cereal prices could structurally spike by up to 40%. These findings provide a replicable pipeline from climate tipping points to human impact, underscoring the urgent necessity of preemptive, climate-resilient food infrastructure.

What places on Earth are most resilient to global catastrophic risk (GCR)? We provide the first study of what locations are more resilient against the impacts of nuclear war, near‐Earth objects, large‐magnitude volcanic eruptions, large‐scale cyberattacks, high altitude electromagnetic pulse, geomagnetic storms and pandemics. This shows there is no place on Earth which is resilient against all kinds of GCR. Australia shows resilience across the widest range of GCR scenarios in the literature we reviewed, but even for it, continued international cooperation and trade are essential. Across the different risks, common resilience factors that show up most are geographic isolation (e.g. islands), self‐sufficiency (especially in food production), high governance quality (more democratic and lower inequality) and decentralization to mitigate single point catastrophic failures (e.g. impacting trade or food supply). Many of these factors stand in tension with each other and trade‐offs are required to balance between different GCR scenarios and between a higher resilience against the immediate impacts or against the longer‐term consequences. The literature suggests that increased GCR resilience requires more investment in preparation (e.g., food security), planning (e.g., national risk assessments), and international agreements that facilitate cooperation on preparation and GCR response.

Exploring uncertain timelines and consequences

Exploring uncertain timelines and consequences

And why we only talk about looming catastrophe

And why we only talk about looming catastrophe

Food is the foundation of our society. We often take it for granted, but stocks are rarely available for longer than a year, and food production can be disrupted by catastrophic events, both locally and globally. To highlight such major risks to the food system, we analyzed FAO crop production data from 1961 to 2023 to find the largest crop production shock for every country and identify its causes. We show that large crop production shocks regularly happen in all countries. This is most often driven by climate (especially droughts), but disruptions by other causes like economic disruptions, environmental hazards (especially storms) and conflict also occur regularly. The global mean of largest country-level shocks averaged -29%, with African countries experiencing the most extreme collapses (-80% in Botswana), while Asian and Central European nations faced more moderate largest shocks (-5 to -15%). While global shocks above 5% are rare (occurring once in 63 years), continent-level shocks of this magnitude happen every 1.8 years on average. These results show that large disruptions to our food system frequently happen on a local to regional scale and can plausibly happen on a global scale as well. We therefore argue that more preparation and planning are needed to avoid such global disruptions to food production.