Climate disruptions following a nuclear conflict would substantially affect food security, putting large parts of mankind at risk of starvation as has been shown by climate-crop modelling studies. Yet, earlier studies did not integrate comprehensive uncertainties in crop models across various intensities of climate perturbations from different levels of atmospheric soot injection, the potentials and limitations of adaptation such as timing of growing seasons or crop choice, and further disruptions in agricultural production such as fertilizer and labor shortages. Herein, we propose a project that will set out to address these research gaps by harnessing the comprehensive crop modelling capacities of the Global Gridded Crop Model Intercomparison (GGCMI) ensemble to simulate secondary climatic impacts of nuclear conflict on global crop production at various levels of stratospheric soot injection for the above adaptation options and extended impacts. This will provide the thus far most comprehensive assessment of potential impacts on crop production and the available option space for adaptation under the working hypotheses that adaptation potential is limited and supply chain disruptions may substantially exacerbate impacts already at lower intensities of soot injection.

Recent threats and growing nuclear arsenals are increasing the risk of a nuclear war. Besides the immediate threat of nuclear-weapon explosions, many uncertainties remain about the impact on climate of the subsequent widespread fires as the emitted particles are able to interact with solar radiation. Currently, previous studies have injected only soot over a very short time frame (1 day or one-model time step) and have not included any other particles such as organic or brown carbon that can be over 10 times larger in amount compared to soot during, for example, forest fires.In this study, we will use a set of models of different complexity from a fire-plume model to a fully coupled Earth System Model to investigate the plume composition, its development and climate effects of the smoke generated by fires following a regional nuclear war. Our results will then be shared with other research groups to be used to drive crop and fishery models to estimate the impacts on food availability following a nuclear conflict. Our results will also be compared to previous modeling studies to provide a more robust estimate of the climate consequences associated with a nuclear war.

The potential destruction of the ozone layer by nuclear war poses grave dangers to humanity and ecosystems. In addition to direct effects on surface climate, previous studies of regional scale nuclear exchanges and associated fires have considered how injection of reactive nitrogen and smoke heating could deplete stratospheric ozone. However, studies of urban fires provide evidence for substantial emissions of chlorine, bromine and possibly iodine compounds (for example, from the burning of plastics, flame retardants, home insulation, medical materials, etc.). We propose to evaluate how much these potent ozone-destroying chemicals would add to current estimates of ozone loss following nuclear exchanges. Further, new studies in our group have altered the fundamental understanding of atmospheric chemistry impacts of fire smoke, and are highly likely to increase expected stratospheric ozone losses following nuclear war from these emissions. We have shown that greatly enhanced solubility of hydrochloric acid in oxidized organic smoke particles enhances chlorine-catalyzed ozone destruction. While the Antarctic ozone hole is currently slated to recover by the 2060s, we will probe the extent to which a nuclear exchange could not only bring it back but make it global, i.e., reversing one of humanity's great environmental achievements and driving widespread devastation.

We recently quantified how the climate change caused by atmospheric soot loadings from nuclear weapon detonation would limit terrestrial and aquatic food production. We used one climate model, one crop model, and one fishery model to estimate the impacts from six scenarios of stratospheric soot injection, predicting the total food calories available in each nation post-war after stored food was consumed. We estimated that more than 2 billion people could die from nuclear war between India and Pakistan, and more than 5 billion could die from a war between the United States and Russia. We propose to work with other scientific teams to refine and advance our work by using multiple climate and crop models, and addressing changes in the availability of fuel, fertilizer, and agricultural infrastructure, the effects of radioactive contamination, adaptation measures such as planting different crops, and assumptions about food distribution within nations and trade between nations. We will create software for nuclear states to use so they can calculate and avoid civilian deaths depending on how they plan to use nuclear weapons. We will communicate our results with talks, publications, and social media, to inform public policy of the consequences of any use of nuclear weapons.

Crop models indicate substantial detrimental impacts on global crop production under nuclear conflict (NC) scenarios. However, crop models have mainly been developed for assessing climate change impacts, focussing on the effects of warming and drought, giving little attention to yield penalties associated with frost damage, excess soil moisture, and flooding. The climate damage mechanisms associated with cooling and excess soil moisture are particularly relevant for evaluating impacts due to NC, but current process-based crop models have limited capacity to represent the associated impacts, leading to overly optimistic impact projections. Here, we propose to improve three well-established global gridded crop models (LPJmL, pDSSAT, CLM-crop) with respect to responses to excess moisture and cold temperatures, based on the expertise from AgMIP’s Global Gridded Crop Model Intercomparison (GGCMI). Flood damage will be accounted for in post-processing based on inundation estimates from an external flood model. These results also help to put into perspective results from a partner project that generates a large ensemble of crop model projections under different NC and management scenarios. Conclusions from this work provide new and corroborated quantitative evidence for the catastrophic indirect but global effects of nuclear conflict.

Model studies suggest that intense fires subsequent to the detonation of nuclear warheads would create so-called ‘nuclear-winters’ that could persist for many years leading to global famine. Even regional-scale wars could pose an existential threat to ecosystems and humanity. Here, we utilise a fully-coupled version of the UKESM1 Earth System model to assess the impacts of three different nuclear scenarios i) all-out USA-Russia nuclear war, ii) war between India-Pakistan, iii) more limited nuclear conflicts in eastern Europe. Different numbers of nuclear detonations, vertical profiles, and seasons of conflict are assumed over each area and the climate response is analysed over the subsequent twenty year period. For USA-Russia and India-Pakistan nuclear scenarios, the results are compared to those from significantly less sophisticated and significantly coarser resolution models to examine the fidelity of the earlier results. The new scenarios examine the climatic impacts of the detonation of as few as ten Hiroshima sized nuclear warheads over eastern Europe. Analyses include the physical evolution and longevity of the stratospheric plume and the response in terms of near-surface temperatures, precipitation, stratospheric ozone, induced changes in atmospheric and ocean dynamics, impacts on net primary productivity, ecosystem adaptability and impacts on crop productivity.

There are many uncertainties in assessing the consequences of nuclear conflict. Here I propose to work on several outstanding questions, and to communicate the results to society at large. Tasks include:1. I propose to finish a list of military targets in the U.S. and other NATO countries, as well as in Russia and its allies. 2. I propose a modern analysis of the fatalities and casualties from the explosions to gain a better estimate of direct effects. 3. The greatest danger to the global population in a nuclear war is from climate changes due to smoke from fires. I propose to complete a data base of black carbon and smoke emission factors. We will use that data base to determine how much smoke and black carbon will be emitted in a global nuclear war. 4. Using these new targets, and emission factors we will conduct a series of climate modeling studies to determine how military targets compare with urban targets in terms of casualties and impacts on climate. We will also investigate how the components of the smoke other than black carbon contribute to the climate changes assuming the other components are mainly organics.

This project will create two new pieces of software, OpenSIOP and TARGETMAP. OpenSIOP is an application designed to make the curation of nuclear war scenarios by researchers easier, quicker, and more transparent. It is an open-source framework for managing datasets of possible nuclear targets, national nuclear arsenals, and target allocations. It will allow expert researchers to easily share and modify target sets, create subsets of targets on the basis of sophisticated targeting philosophies, create force allocations (war scenarios) based on those targets, and export these results to other tools for consequence estimation. It will also be designed to accommodate historical data and methodologies. At every stage, this development will be informed by close communication with other researchers working on the humanitarian impacts of nuclear weapons. TARGETMAP will be built upon the data model developed for OpenSIOP as a public-facing tool for lay audiences to visualize nuclear war scenarios across time and enable them to think concretely about the nature of nuclear war and its impacts. These two tools have the potential to radically improve and enhance academic research into realistic nuclear war scenarios, both in the present and past, as well as facilitate an increased level of engagement with the topic than has ever been possible among lay (and journalist) audiences.

Nearly all organic material on Earth is produced by photosynthesizing organisms that play a critical role in food web dynamics, providing the energy needed to sustain consumers at higher trophic levels, including humans. Studies conducted with chemistry-climate models suggest that the firestorms associated with a potential nuclear conflict destroy the protective stratospheric ozone layer, exposing critical photosynthesizers to high levels of UV radiation. Despite the potentially devastating impacts, few studies have investigated the effects of postnuclear UV radiation perturbations on terrestrial and marine photosynthesizers. In this project, we will use a state-of-the-art Earth system model to simulate the response of terrestrial and marine primary production to postnuclear UV radiation. We will modify an existing model to include parameterizations for damage by UV radiation for different types of crops, plants, and marine phytoplankton. We aim to conduct multiple simulations with the modified model to produce a detailed quantification of the sensitivity of photosynthesizers to postnuclear UV radiation and to assess the potential for cascading impacts of nuclear conflict on ecosystem integrity and food security.

We propose to develop a framework to simulate urban-scale fires resulting from regional nuclear blasts. It will leverage data on urban morphology and results from simulations performed with a coupled urban-fire-atmosphere model to produce heat and aerosol emissions from burning cities. It will also simulate the evolution of resulting urban pyroconvective smoke plumes, as well as their vertical distribution and final injection level. The effort will leverage the existing fire-atmosphere model WRF-SFIRE-CHEM, which couples a fire spread model and the chemistry version of the Weather Research and Forecasting Model (WRF-Chem) linked with an advanced urbanized version of WRF. Existing wildfire spread and fuel consumption modules will be complemented by the urban fire model, leveraging detailed urban morphological information from the WUDAPT methodology to estimate urban fire heat and emission fluxes. The resulting urban-fire model will allow urban, meteorological, as well as fire processes and interactions, to be resolved in one integrated modeling framework. This will allow us to estimate vertical distributions of emission fluxes, plume rise, and smoke aerosol concentrations, and will allow NW modeling of groups of burning cities anywhere in the world, with simulated detailed characteristics of pyroconvection and emissions from urban fires initiated by nuclear explosions.