Comments
A preliminary estimate, and a request for better ones.
Summary
I believe the standard literature estimates for the number of DALYs attributable to a case of stunting are too low, largely because they don’t account for the long term effects. This means that childhood nutritional interventions that reduce the prevalence of stunting may be substantially more cost-effective than previously believed.
Epistemic status
Exploratory and back-o...
I think the general answer for non-military threats is going to be "the Civil Service", in branches that deal with the respective area (health, climate impact, food supply chain, tech policy, space assets) with academics and businesspeople and policy wonks consulted for expertise, and the government getting their own Special Advisers on the case when they're planning policy. Generally they're going to be interested in threats to people in the UK and the UK economy in general rather than purely existential threats. I'm not sure what sort of models of farming and industry you're envisaging, but the Office for National Statistics and various budget and health and weather forecasting related bodies do loads of modelling work of varying quality. I'm just not sure much of it relates to x-risk.
I suppose I'm interested in questions around what is an existential threat. How bad a nuclear winter would it have to be to cause the collapse of society (and how easily could society be rebuilt afterwards). Both require robust models of agriculture in extreme situations and models of energy flows in economies where strategic elements might have been destroyed (to know how easy rebuilding would be). Since pandemic/climate change also have societal collapse as a threat the models needed would apply to them too (they might trigger nuclear exchange or at least loss of control over nuclear reactors, depending upon what societal collapse looks like).
The national risk register is the closest I found, in the public domain. It doesn't include things like large meteorites, that I found.