Thanks for writing this I thought it was very clear and so upvoted. I disagree with both claims 1 and 2 and will try to explain why.
I think there are ways to constrain climate damages. This is what the climate economics literature tries to do. That literature has come in for some justified criticism in recent years for using out of date literature and being a bit of a mess. However, it remains true that recent studies using recent data that try to add up all of the costs of climate change that people talk about tend to find that the monetised value of the costs of 4 degrees C are equivalent to a 5-10% counterfactual reduction in GDP 2100 relative to a world without climate change. This is not relative to today, it is relative to 2100. On all plausible socioeconomic scenarios, income per head will have grown by at least several hundred % up to 2100, so average living standards will be higher.
To give one example, Takakura et al add up impacts from
Changes in agricultural productivity
Undernourishment
Heat-related excess mortality
Cooling/heating demand
Occupational-health costs
Hydroelectric generation capacity
Thermal power generation capacity
Fluvial flooding and coastal inundation
Their model produces the following results. Note that RCP4.5 is now widely seen as ‘business as usual’, and it implies about 2.7 degrees above pre-industrial. The monetized impact is about 2% of GDP in 2100 relative to a counterfactual without climate change. For RCP8.5, which implies about 4.4 degrees (there is <5% chance of this on current policy) implies a monetized cost of 5-10% of GDP.
Which impact channel do you think this model is missing such that its estimates are wrong by 2,000%?
There is one model by Burke et al (2015) that finds that GDP will be 25% lower in 2100, with a 5% chance it will be 60% lower in 2100 relative to a counterfactual without climate change. This is a massive outlier relative to the rest of the literature, but even this model does not find that average living standards would decline. This study tries to calculate the costs of warming using historical data on interannual weather variation, and I personally don’t trust it, as I will try to explain in a forthcoming report.
In summary, most economic models project that 4K of warming would do damage equivalent to knocking 5% of GDP in a world in which incomes would be much higher due to economic growth. No models project that living standards would decline relative to today. If your claim were true, one would have thought that at least some models would predict a decline in living standards.
This literature would have to be very dramatically wrong in order to justify the claim that climate change is comparable to biorisk and AI. My views on AI and bio are as follows: I believe that there is >20% chance that civilisation will be completely upended in the next 20-30 years, with outcomes as bad as a >50% decline in GDP relative to today. No-one who has tried to develop a model and add up the costs of climate change according to the latest literature thinks that this is true of climate change. So in my view it is unreasonable to think that climate change is in a similar ballpark. I also think nuclear war risk is far greater.
Independently, it is just hard to see why 3K would do such massive damage. The world has warmed by nearly a degree since 1980 and average living standards increased by several hundred %. What is the actual mechanism whereby an extra 2K would cause the collapse of civilisation? Civilisations thrive at very different temperatures across the globe—eg the southern US is more than 3K warmer than the northern US—and people live through very large seasonal and diurnal temperature changes. What is meant to happen at 3k which would destroy civilisation?
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.
Skepticism of the Takakura paper / economic modelling of climate damages
I’m somewhat skeptical of the Takakura paper you mention. First, 2% loss in GDP relative to the counterfactual at 2.7 degrees just seems way too small. I think this is partly due to this paper, which whilst a bit emotive, seems to point out some quite major flaws in Nordhaus’ methodology for calculating climate damages (e.g. 90% of GDP will be unaffected as it happens indoors) who also arrived at 2.1% at 3 degrees warming. Keen in that paper also seems to think that due to the assumption above, plus using the impact of current temperatures on GDP (as you did at the end of your comment, see below), Nordhaus might be underestimating climate damages by an order of magnitude, bringing it to 20%. I feel like a model which has serious methodological flaws (Nordhaus) which produces answer similar to Takakura indicates that Takakura also has things that it hasn’t accounted for.
Independently, it is just hard to see why 3K would do such massive damage. The world has warmed by nearly a degree since 1980 and average living standards increased by several hundred %. What is the actual mechanism whereby an extra 2K would cause the collapse of civilisation?
Like above, I think due to nonlinearity in climate impacts/damages, it doesn’t make sense to that a 1.2 degree temperature increase with little/no impact on living standards will scale up to 3 degrees of warming with also very little impact on living standards.
In terms of the mechanism, there’s credible IPCC estimates that put forced migration due to climate change between 25-1000 million people, with a potential median of 200 million people by 2050. In my opinion, forced migration of that scale could play a role in societal destabilisation, even though the chances of this happening might only be quite small (e.g.5%). For example, there is nothing in Takakura about impact of forced migration, civil unrest, etc, which could also mean they’ve underestimated the GDP impacts. There’s probably many other mechanisms they’ve not been able to include, and the world is very complex, so it seems overconfident to put a lot of weight on one paper that only models 9 specific impacts.
Uncertainty on GDP being a good predictor of x-risk
Otherwise, I’m not even sure that GDP is the best indicator of the probability of x-risk posed by climate change. Even in Takakura’s paper, they say that:
We used the percentage of GDP as an impact indicator but we do not claim it is the best or only indicator to evaluate the impacts of climate change.
For example, one could make a similar claim for AI analogous to what you said about climate:
The world has warmed by nearly a degree since 1980 and average living standards increased by several hundred %.
namely: “AI and ML algorithms have developed exponentially in the past 50 years, yet living standards have only gotten better. So how could additional improvements in ML or AI lead to existential risk?”
Whilst this example probably isn’t perfect, I think it highlights how the past isn’t necessarily a good predictor of future x-risk from certain scenarios. Whilst the AI scenario might lead to more of a rapidly worsening scenario if we develop misaligned AGI, it’s feasible that passing climate tipping points would trigger a serious increase in x-risk that economic models or past GDP metrics fail to account for.
Note that the Takakura paper was not cherry picked as shown in the chart below from the IPCC
The big outlier in green is Burke, but the structural modelling studies that add up the costs of climate change in different sectors tend to put the costs of climate change at <10%.
I don’t think a criticism of Nordhaus’ model is a criticism of Takakura’s model. They are quite different. I agree that the Nordhaus stuff is very flawed. Unfortunately, I think that because of these flaws, people have written off the whole of climate economics, which on the whole produces similar findings to Nordhaus, and not all of which is flawed. I checked their references, and Takakura uses up to date literature on all of the impact mechanisms.
I agree that they don’t cover indirect risks. I would view the literature as a good estimate of the direct costs of climate change, which are less than 10% of GDP. It is still a useful corrective to views like Lynas and others that due to the direct effects on agriculture and the like, the chance of civilisational collapse is at 3C is like 30%.
To be clear, they are not measuring costs that would show up in GDP statistics. They are measuring the welfare costs of climate change expressed in monetised terms, so including effects on health, output and so on.
I take the ding on the AI/ML growth analogy.
If the claim is that the indirect risks of 3C are large enough to destabilise civilisation because displacement would lead to nuclear war or something then we can argue the toss on that one (perhaps now?). But if the claim is that the direct costs are sufficient to destroy civilisation, as Lynas and others seem to think, I just think that is just clearly wrong
Thanks for writing this I thought it was very clear and so upvoted. I disagree with both claims 1 and 2 and will try to explain why.
I think there are ways to constrain climate damages. This is what the climate economics literature tries to do. That literature has come in for some justified criticism in recent years for using out of date literature and being a bit of a mess. However, it remains true that recent studies using recent data that try to add up all of the costs of climate change that people talk about tend to find that the monetised value of the costs of 4 degrees C are equivalent to a 5-10% counterfactual reduction in GDP 2100 relative to a world without climate change. This is not relative to today, it is relative to 2100. On all plausible socioeconomic scenarios, income per head will have grown by at least several hundred % up to 2100, so average living standards will be higher.
To give one example, Takakura et al add up impacts from
Changes in agricultural productivity
Undernourishment
Heat-related excess mortality
Cooling/heating demand
Occupational-health costs
Hydroelectric generation capacity
Thermal power generation capacity
Fluvial flooding and coastal inundation
Their model produces the following results. Note that RCP4.5 is now widely seen as ‘business as usual’, and it implies about 2.7 degrees above pre-industrial. The monetized impact is about 2% of GDP in 2100 relative to a counterfactual without climate change. For RCP8.5, which implies about 4.4 degrees (there is <5% chance of this on current policy) implies a monetized cost of 5-10% of GDP.
Which impact channel do you think this model is missing such that its estimates are wrong by 2,000%?
There is one model by Burke et al (2015) that finds that GDP will be 25% lower in 2100, with a 5% chance it will be 60% lower in 2100 relative to a counterfactual without climate change. This is a massive outlier relative to the rest of the literature, but even this model does not find that average living standards would decline. This study tries to calculate the costs of warming using historical data on interannual weather variation, and I personally don’t trust it, as I will try to explain in a forthcoming report.
In summary, most economic models project that 4K of warming would do damage equivalent to knocking 5% of GDP in a world in which incomes would be much higher due to economic growth. No models project that living standards would decline relative to today. If your claim were true, one would have thought that at least some models would predict a decline in living standards.
This literature would have to be very dramatically wrong in order to justify the claim that climate change is comparable to biorisk and AI. My views on AI and bio are as follows: I believe that there is >20% chance that civilisation will be completely upended in the next 20-30 years, with outcomes as bad as a >50% decline in GDP relative to today. No-one who has tried to develop a model and add up the costs of climate change according to the latest literature thinks that this is true of climate change. So in my view it is unreasonable to think that climate change is in a similar ballpark. I also think nuclear war risk is far greater.
Independently, it is just hard to see why 3K would do such massive damage. The world has warmed by nearly a degree since 1980 and average living standards increased by several hundred %. What is the actual mechanism whereby an extra 2K would cause the collapse of civilisation? Civilisations thrive at very different temperatures across the globe—eg the southern US is more than 3K warmer than the northern US—and people live through very large seasonal and diurnal temperature changes. What is meant to happen at 3k which would destroy civilisation?
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.
Skepticism of the Takakura paper / economic modelling of climate damages
I’m somewhat skeptical of the Takakura paper you mention. First, 2% loss in GDP relative to the counterfactual at 2.7 degrees just seems way too small. I think this is partly due to this paper, which whilst a bit emotive, seems to point out some quite major flaws in Nordhaus’ methodology for calculating climate damages (e.g. 90% of GDP will be unaffected as it happens indoors) who also arrived at 2.1% at 3 degrees warming. Keen in that paper also seems to think that due to the assumption above, plus using the impact of current temperatures on GDP (as you did at the end of your comment, see below), Nordhaus might be underestimating climate damages by an order of magnitude, bringing it to 20%. I feel like a model which has serious methodological flaws (Nordhaus) which produces answer similar to Takakura indicates that Takakura also has things that it hasn’t accounted for.
Like above, I think due to nonlinearity in climate impacts/damages, it doesn’t make sense to that a 1.2 degree temperature increase with little/no impact on living standards will scale up to 3 degrees of warming with also very little impact on living standards.
In terms of the mechanism, there’s credible IPCC estimates that put forced migration due to climate change between 25-1000 million people, with a potential median of 200 million people by 2050. In my opinion, forced migration of that scale could play a role in societal destabilisation, even though the chances of this happening might only be quite small (e.g.5%). For example, there is nothing in Takakura about impact of forced migration, civil unrest, etc, which could also mean they’ve underestimated the GDP impacts. There’s probably many other mechanisms they’ve not been able to include, and the world is very complex, so it seems overconfident to put a lot of weight on one paper that only models 9 specific impacts.
Uncertainty on GDP being a good predictor of x-risk
Otherwise, I’m not even sure that GDP is the best indicator of the probability of x-risk posed by climate change. Even in Takakura’s paper, they say that:
For example, one could make a similar claim for AI analogous to what you said about climate:
namely: “AI and ML algorithms have developed exponentially in the past 50 years, yet living standards have only gotten better. So how could additional improvements in ML or AI lead to existential risk?”
Whilst this example probably isn’t perfect, I think it highlights how the past isn’t necessarily a good predictor of future x-risk from certain scenarios. Whilst the AI scenario might lead to more of a rapidly worsening scenario if we develop misaligned AGI, it’s feasible that passing climate tipping points would trigger a serious increase in x-risk that economic models or past GDP metrics fail to account for.
Hi James, thanks for this.
Note that the Takakura paper was not cherry picked as shown in the chart below from the IPCC
The big outlier in green is Burke, but the structural modelling studies that add up the costs of climate change in different sectors tend to put the costs of climate change at <10%.
I don’t think a criticism of Nordhaus’ model is a criticism of Takakura’s model. They are quite different. I agree that the Nordhaus stuff is very flawed. Unfortunately, I think that because of these flaws, people have written off the whole of climate economics, which on the whole produces similar findings to Nordhaus, and not all of which is flawed. I checked their references, and Takakura uses up to date literature on all of the impact mechanisms.
I agree that they don’t cover indirect risks. I would view the literature as a good estimate of the direct costs of climate change, which are less than 10% of GDP. It is still a useful corrective to views like Lynas and others that due to the direct effects on agriculture and the like, the chance of civilisational collapse is at 3C is like 30%.
To be clear, they are not measuring costs that would show up in GDP statistics. They are measuring the welfare costs of climate change expressed in monetised terms, so including effects on health, output and so on.
I take the ding on the AI/ML growth analogy.
If the claim is that the indirect risks of 3C are large enough to destabilise civilisation because displacement would lead to nuclear war or something then we can argue the toss on that one (perhaps now?). But if the claim is that the direct costs are sufficient to destroy civilisation, as Lynas and others seem to think, I just think that is just clearly wrong