While I do suggest a 0.1% probability of existential catastrophe from climate change, note that this is on my more restricted definition, where that is roughly the chance that humanity loses almost all its longterm potential due to a climate catastrophe. On Beard et al’s looser definition, I might put that quite a bit higher (e.g. I think there is something more like a 1% chance of a deep civilisation collapse from climate change, but that in most such outcomes we would eventually recover). And I’d put the risk factor from climate change quite a bit higher than 0.1% too — I think it is more of a risk factor than a direct risk.
The problem in my view, is that climate change could, if severe enough (say >3.5 degrees before 2100) become a “universal stressor”, increasing the probability of various risks that in turn make other risks more likely. For example: economic stagnation, institutional decay, political instability, inter-state conflicts, great power conflicts, zoonotic spillover events, large and destabilizing refugee flows, famine, etc. Every item on this list is made more likely in a warmer planet, but also made worse, because we will have fewer resources to deal with them.
Each of these adverse events also increases the risk of other adverse events. So even if CC only increases the risk of each event by a small percent, the total risk added to the system could be considerable.
With regards to the worst risks, this becomes even more problematic. Consider a nuclear winter scenario. That is pretty bad. But a nuclear winter scenario in combination (partly caused by) with a severe climate crisis is much worse (since CC will affect many countries that will be spared from NW, but also because countries suffering from CC will have fewer resources to help refugees etc).
Now consider the added risk that a zoonotic spillover event might happen. This is also made more likely by CC. But in the case that we combine social collapse due to CC with zoonotic spillover it becomes more and more difficult to see a path from there to recovery.
While I do suggest a 0.1% probability of existential catastrophe from climate change, note that this is on my more restricted definition, where that is roughly the chance that humanity loses almost all its longterm potential due to a climate catastrophe. On Beard et al’s looser definition, I might put that quite a bit higher (e.g. I think there is something more like a 1% chance of a deep civilisation collapse from climate change, but that in most such outcomes we would eventually recover). And I’d put the risk factor from climate change quite a bit higher than 0.1% too — I think it is more of a risk factor than a direct risk.
The problem in my view, is that climate change could, if severe enough (say >3.5 degrees before 2100) become a “universal stressor”, increasing the probability of various risks that in turn make other risks more likely. For example: economic stagnation, institutional decay, political instability, inter-state conflicts, great power conflicts, zoonotic spillover events, large and destabilizing refugee flows, famine, etc. Every item on this list is made more likely in a warmer planet, but also made worse, because we will have fewer resources to deal with them.
Each of these adverse events also increases the risk of other adverse events. So even if CC only increases the risk of each event by a small percent, the total risk added to the system could be considerable.
With regards to the worst risks, this becomes even more problematic. Consider a nuclear winter scenario. That is pretty bad. But a nuclear winter scenario in combination (partly caused by) with a severe climate crisis is much worse (since CC will affect many countries that will be spared from NW, but also because countries suffering from CC will have fewer resources to help refugees etc).
Now consider the added risk that a zoonotic spillover event might happen. This is also made more likely by CC. But in the case that we combine social collapse due to CC with zoonotic spillover it becomes more and more difficult to see a path from there to recovery.
FWIW this seems too high, although “any major catastrophe commonly associated with these things” could be interpreted broadly.
Edit: Meant FWIW not FYI, FYI would be a bit aggressive here.