Thanks for your comments, for the detailed response, and for upvoting on clarity rather than agreement! I’m looking forward to your upcoming report.
I am not enough of an expert on the economic models at this moment for a debate on the detailed ins and outs of the models to be particularly productive. Nevertheless I do have a lot of experience with mathematical modeling in general, and particularly in modeling systems with nonlinear phenomena (i.e. cascading/systemic effects). From this background, I find the complete absence from these models of phenomena that will almost obviously be key drivers in any global collapse (war, mass migration, etc. --- which are notably missing from the list you give) rather disturbing. As I said in the text, there is no way that models excluding phenomenon X can give you a reasonable estimate for the likelihood of X.
Of course things like war and mass migration are missing from the models because they’re really hard to model, and so you can’t fault the economic modelers for that. But all models are a crude abstraction of reality anyway; what’s important is whether, for the scenario being studied, the models describe the real world in any useful way. I gladly concede that economic models are helpful for predicting, e.g. “small” changes in GDP due to climate change, but see no grounds yet for moderating my skepticism on their ability to say anything meaningful about risks of collapse.
I emphasize that these are not good grounds for thinking that the collapse risk is very high, and this is also not the position I am defending! But they are good grounds for being skeptical of the ability for current models to truly constrain the probability of these extreme scenarios.
I think this is too bearish on the economic modeling. If you want to argue that climate change could pose some risk of civilization collapse, you have to argue that some pathway exists from climate to a direct impact on society that prevents the society from functioning. When discussing collapse scenarios from climate most people (I think) are envisiging food, water, or energy production becoming so difficult that this causes further societal failures. But the economic models strongly suggest that the perturbations on these fronts are only “small”, so that we shouldn’t expect these to lead to a collapse. I think in this regime we should trust the economic modeling. If instead the economic models were finding really large effects (say, a 50% reduction in food production), then I would agree that the economic models were no longer reliable. At this point society would be functioning in a very different regime from present, so we wouldn’t expect the economic modeling to be very useful.
You could argue that the economic models are missing some other effect that could cause collapse, but I think it is difficult to tell such a story. The story that climate change will increase the number of wars is fairly speculative, and then you would have to argue that war could cause collapse, which is implausible excepting nuclear war. I think there is something to this story, but would be surprised if climate change were the predominant factor in whether we have a nuclear war in the next century.
Famine induced mass migration also seems very unlikely to cause civilization collapse. It would be very easy with modern technology for a wealthy country to defend itself against arbitrarily large groups of desperate, starving refuges. Indeed, to my knowledge there has been no analogy for a famine->mass migration->collapse of neighbouring society chain of events in the historic record, despite many horrific famines. I haven’t investigated this quesiton in detail however, and would be very interested if such events have in fact occurred.
Thanks for the perspective! I agree in part with your point about trusting the models while the perturbations they predict are small, but even then I’d say that there are two very different possibilities:
we can safely ignore real-world nonlinearities, cascading effects, etc., because the economic models suggest the perturbations are small.
the predicted perturbations are small because the economic models neglect key real-world nonlinearities and cascading effects.
As long as we think the second option is plausible enough, strong skepticism of the models remains justified. I don’t claim to know what’s actually the case here—this seems like a pretty important thing to work on understanding better.
I don’t understand 2. The neglected cascading effects have to cascade from somewhere. You are saying that the model could be missing an effect on the variables in its system from variables outside the system. But the variables outside the system you highlight are only going to be activated when the variables in the system are highly perturbed!
Forgetting the models for a second, if the only causal story to wars and mass migration that we can think of goes through high levels of economic disruption, then it is sufficient to see small levels of economic disruption and conclude that wars and mass migration are very unlikely.
I do not think that “small levels” is necessarily what we see—increased rates of natural disasters have really substantial effects on migration and could produce localized resource conflicts. But those don’t seem large scale enough to trigger global catastrophes.
I agree with Damon’s comment. To add to that, in the post, you appeal to Mark Lynas’ opinion on the risk of collapse due to climate change. But he thinks civilisation will collapse due to the direct effects.
Another point is that economic models can shed light on how big the indirect effects are meant to be. Presumably if something has larger direct effects, then it will have larger indirect effects, as a rule. If the models are correct and the direct costs of climate change of 2-3C are equivalent to ~5% GDP, that would put it in the ballpark many other problems that constrain global welfare, like housing regulation, poor pricing of water, underinvestment in R&D, the lack of a land value tax, etc. But few argue that these sorts of problems are a key driver of the risk of nuclear war this century.
Thanks for your comments, for the detailed response, and for upvoting on clarity rather than agreement! I’m looking forward to your upcoming report.
I am not enough of an expert on the economic models at this moment for a debate on the detailed ins and outs of the models to be particularly productive. Nevertheless I do have a lot of experience with mathematical modeling in general, and particularly in modeling systems with nonlinear phenomena (i.e. cascading/systemic effects). From this background, I find the complete absence from these models of phenomena that will almost obviously be key drivers in any global collapse (war, mass migration, etc. --- which are notably missing from the list you give) rather disturbing. As I said in the text, there is no way that models excluding phenomenon X can give you a reasonable estimate for the likelihood of X.
Of course things like war and mass migration are missing from the models because they’re really hard to model, and so you can’t fault the economic modelers for that. But all models are a crude abstraction of reality anyway; what’s important is whether, for the scenario being studied, the models describe the real world in any useful way. I gladly concede that economic models are helpful for predicting, e.g. “small” changes in GDP due to climate change, but see no grounds yet for moderating my skepticism on their ability to say anything meaningful about risks of collapse.
I emphasize that these are not good grounds for thinking that the collapse risk is very high, and this is also not the position I am defending! But they are good grounds for being skeptical of the ability for current models to truly constrain the probability of these extreme scenarios.
I think this is too bearish on the economic modeling. If you want to argue that climate change could pose some risk of civilization collapse, you have to argue that some pathway exists from climate to a direct impact on society that prevents the society from functioning. When discussing collapse scenarios from climate most people (I think) are envisiging food, water, or energy production becoming so difficult that this causes further societal failures. But the economic models strongly suggest that the perturbations on these fronts are only “small”, so that we shouldn’t expect these to lead to a collapse. I think in this regime we should trust the economic modeling. If instead the economic models were finding really large effects (say, a 50% reduction in food production), then I would agree that the economic models were no longer reliable. At this point society would be functioning in a very different regime from present, so we wouldn’t expect the economic modeling to be very useful.
You could argue that the economic models are missing some other effect that could cause collapse, but I think it is difficult to tell such a story. The story that climate change will increase the number of wars is fairly speculative, and then you would have to argue that war could cause collapse, which is implausible excepting nuclear war. I think there is something to this story, but would be surprised if climate change were the predominant factor in whether we have a nuclear war in the next century.
Famine induced mass migration also seems very unlikely to cause civilization collapse. It would be very easy with modern technology for a wealthy country to defend itself against arbitrarily large groups of desperate, starving refuges. Indeed, to my knowledge there has been no analogy for a famine->mass migration->collapse of neighbouring society chain of events in the historic record, despite many horrific famines. I haven’t investigated this quesiton in detail however, and would be very interested if such events have in fact occurred.
Thanks for the perspective! I agree in part with your point about trusting the models while the perturbations they predict are small, but even then I’d say that there are two very different possibilities:
we can safely ignore real-world nonlinearities, cascading effects, etc., because the economic models suggest the perturbations are small.
the predicted perturbations are small because the economic models neglect key real-world nonlinearities and cascading effects.
As long as we think the second option is plausible enough, strong skepticism of the models remains justified. I don’t claim to know what’s actually the case here—this seems like a pretty important thing to work on understanding better.
I don’t understand 2. The neglected cascading effects have to cascade from somewhere. You are saying that the model could be missing an effect on the variables in its system from variables outside the system. But the variables outside the system you highlight are only going to be activated when the variables in the system are highly perturbed!
Forgetting the models for a second, if the only causal story to wars and mass migration that we can think of goes through high levels of economic disruption, then it is sufficient to see small levels of economic disruption and conclude that wars and mass migration are very unlikely.
I do not think that “small levels” is necessarily what we see—increased rates of natural disasters have really substantial effects on migration and could produce localized resource conflicts. But those don’t seem large scale enough to trigger global catastrophes.
I agree with Damon’s comment. To add to that, in the post, you appeal to Mark Lynas’ opinion on the risk of collapse due to climate change. But he thinks civilisation will collapse due to the direct effects.
Another point is that economic models can shed light on how big the indirect effects are meant to be. Presumably if something has larger direct effects, then it will have larger indirect effects, as a rule. If the models are correct and the direct costs of climate change of 2-3C are equivalent to ~5% GDP, that would put it in the ballpark many other problems that constrain global welfare, like housing regulation, poor pricing of water, underinvestment in R&D, the lack of a land value tax, etc. But few argue that these sorts of problems are a key driver of the risk of nuclear war this century.