I agree that climate-economy models aren’t good at some types of extremes, but I think there are different versions of this argument, some of which have become weaker over the years. One of Weitzman’s points was that there was a decidedly non-negligible chance of more than 6ºC and our economic models weren’t good at capturing how bad this would be and so tended to underestimate climate risk. I think this was basically right at the time he was writing. But since 5ºC now looks less and less likely, this critique has less and less bite. Because there is such a huge literature on the impact of 5ºC, the models now in principle have a much firmer foundation for damage estimates. eg the Takakura 2019 paper that I go on about in the report uses up to date literature on a wide range of impact channels, but still only gets like a 5% counterfactual reduction in welfare-equivalent of GDP by 2100, and so probably higher average living standards than today.
Another version of this is that the models aren’t good at capturing tipping points. I agree with this, but I also find it difficult to see how this would make a dramatic difference to the damage estimates if you actually drill down into the literature on the impact of different tipping points. Tipping points that might cause different levels of warming are not relevant to damage estimates, so the main ones that seem relevant are ice sheet collapse, regional precipitation and temperature changes, such as changes in monsoons, which might be caused eg by collapse of the AMOC. For the impacts discussed in the literature, it is difficult to see how you get anywhere close to an existential catastrophe if any of these things happen.
Aside from that, it is noteworthy that some economic models actually try to capture the literature on the impact of warming of 5ºC on things like agriculture, sea level rise, temperature-related deaths, lost productivity from heat etc. There is a group of scientists who say that 3ºC/4ºC is catastrophic on the basis of what the scientific literature says about these impacts. The models strongly suggest that they are wrong, and it is not clear what their response is.
All this being said, I am sympathetic to some critiques of the economic models, eg a lot of the Nordhaus stuff. When I was writing the report, I had thought about putting no weight on them at all, but after digging a bit I changed my mind. I think some of the models make a decent stab at quantifying aggregate costs.
I agree that climate changes have contributed at least to some civilisational trauma throughout history. The literature on this suggests that climate change has been correlated with local civilisational trauma. But: (a) local collapse is a far cry from global collapse; (b) most of the time this was due to cooling rather than warming; (c) the mechanism was usually damage to agricultural output, but there is now far more slack in the system, and we have massively better technology to deal with any disruption; (d) we in general have far more advanced technology, and whereas in the past >90% of the workforce would have been employed in agriculture, now <20% is (or whatever); (e) the relationship between climate change and civilisational turmoil breaks down by the industrial revolution, which provides some support for point (c).
The paleoclimate point doesn’t rely on one datapoint: it’s data from 160 million years of climatic and evolutionary history. Massive climate change over that period didn’t cause species extinctions, as some might have expect it to have done.
As you say, with climate change, the extinctions usually happened among marine life, due to ocean anoxia and ocean acidification, and it’s hard to see the mechanism by which CO2 pollution would cause land-based extinctions, unless something else weird happens at the time, such as a volcanic eruption puncturing though salt deposits as happened at the Permian.
For the level of warming that now looks likely of 2-4ºC, it’s really hard to see why it would cause similar damage eg to the Permian, given that the effect is an order of magnitude smaller.
I don’t think they are quasi-arbitrary, they are totally arbitrary. eg they propose a planetary boundary for biodiversity intactness which by their own admission is made up. The boundary also can’t be real since various countries across Eurasia completely destroyed their pre-modern ecosystems after the agricultural revolution without causing anything like civilisational collapse.
A lot of people criticise planetary boundaries for being political advocacy. The clearest evidence for this is Steffen et al proposing a supposed planetary boundary for a ‘Hothouse earth’ at 2ºC (which happens to be the Paris target) on the basis of no argument.
When we are acting under uncertainty I think we should use expected value. Alleged boundaries might be a useful schelling point for political negotiation (like the 2ºC threshold), but it’s not a good approach for actually quantifying risk. Another downside of a boundary is that it implies that anything we do once we pass the boundary is pointless.
Kemp, Jehn and others claim that the effect of warming of more than 3ºC is ‘severely neglected’. But all of the impacts literature explores the effect of rcp8.5 by 2100, which implies 4-5ºC of warming. Jehn’s search strategy uses temperature mentions to measure neglect, but if you use RCP mentions, you don’t get the same result.
My argument here was that I think your argument proves too much—it suggests that the world is extremely fragile to eg agricultural disruption and heat waves that happen all the time. Given that the world was eg a lot poorer in 1980 and so had a lot lower adaptive capacity, why didn’t various weather disasters trigger cascading catastrophes back then? The number of people dying in weather-related disasters has declined massively over time, so we should expect the cascade to have happened in the 1920s and less so in the future?
I also don’t see why cascading risk would change the cause ranking among top causes. Why aren’t democratised bioweapons and AI also cascading risks?
What are the causal pathways that might contribute to conflict risk that you think I have missed? I don’t really get what is meant to happen that I haven’t already discussed. I talk about all of the contributors to war outlined in textbooks about war and combine that with the literature on climate impacts. It is just really a stretch to make it an important contributor to US-China dynamics.
In particular, climate economy models still do bad at the heavy tail, not just of warming, but at civilisational vulnerability etc, again presenting a pretty “middle of the road” rather than heavy tailed distribution. The sort of work from Beard et al 2021 for instance highlights something I think the models pretty profoundly miss. Similarly, I’d be really interested in research similar to Mani et al 2021 on extreme weather events and how this may change due to climate change.
I dpon’t see why the models discount the idea that there is a low but non-negligable probability of catastrophic consequences from 3-4 degrees of warming. What aspect of the models? I’m reticent to rely on things like damage functions here, as they don’t seem to engage with the possib;le heavy-tailedness of damage. Whilst I agree that the models probably are decent approximations of reality, I’m just not really very sure they are useful at telling us anything about the low probabil;ity high impact scenarios that we are worried about here.
Whilst I agree there are reasons to think our vulnerability is less, there is clear reasons to think with a growing interconnected (and potentially fragile) global network and economy, our vulnerability is increasing, meaning that whilst the past collapse data might not be prophetic, there is at least value in it; after all, we are in a very evidence poor environment, meaning that I would be reticent to dismiss it as strongly as you seem to. And whilst it is true our agricultural system is more resilient, there is still a possibility of multiple breadbasket failures etc caused by climate change, and the beard et al and richards et al both explore plausible pathways to this. Again, whilst the past collapse data is definitely not a slam dunk in my favour, I would at least argue it is an update nonetheless. I think you might argue the fact that none led to human extinction makes that data an update in yopur direction, and i think your view on this depends on whether you see collapse and GCR and extinction on a continuum or not; I broadly do, and I assume you broadly don’t?
When I said one data point, I meant really one study. The reason I say this, is as cited, studies of different species/ species groups. In your comment, you don’t seem to engage with Song et al 2021. Kaiho at al 2022 also shows a positive relationship between warming and extinction rate. Moreover, I think it takes an overly confident view of our understanding of kill mechanisms, and seems to suggest that just because we don’t have all what you speculate were the important factors that were present in past mass extinctions doesn’t make that not useful evidence. I think a position like Keller et al 2018 (PETM as the best case, KPg as the worst case) is probably useful at looking at this (only using modern evidence!). Once again, this is an attempt by me, in a low evidence situation, to make best use of the evidence available, and I don’t find your points compelling enough to make me not think that this past precident can’t be informative.
On the Planetary Boundaries, you don’t seem to be engaging with what I’m saying here, which is most alluding to the Baum et al paper on this. Moreover, even if you think we are to use EV, what are you basing the probabilities on? I assume some sort of subjective bayesianism, in which case you’ll have to tell me why I should put a decently high (>1%) prior on moving beyond certain Holocene boundaries posing a genuine threat to humanity? That seems perfectly reasonable to me
I’m not really sure I understand the argument? Whilst in some ways the world has indeed got less vulnerable, in other ways it has got more connected, more economically vulnerable to natural disasters etc. Cascading impact seems to be seen more along these lines than along others. Moreover, if you only had a 5% probability of such a cascade occuring over a century, and we have hardly had a hyper-globalised economy for even that long, why would you expect it to have happened already? Your statements here seem pretty out of step with my actual probabilities etc.. And as I talk about in my talk, I also see problems from AI, biorisk and a whole host more. Thats why this talk, and this approach, is seriously not just about climate change; the hope is to add another approach to studying X-Risk.
I’m also pretty interested in your approach to evidence on X-Risk. I should say from the outset that I think climate change is unlikely to cause a catastrophe, but I don’t think you have provided compelling evidence that the probability is exceptionally small. Your evidence often seems to rely on the very things that we think ought to be suspect in X-Risk scenarios (economic models, continued improved resilience, best case scenario analogies etc.), and you seem to reject some things that might be useful for reasoning in such evidence poor environments (plausibly useful but somewhat flawed historical analogies, foresight, storytelling, scenarios etc.) . Basically, you seem to have a pretty high bar for evidence to be worried about climate change, which whilst I in general think is useful, I’m just not sure how appropriate it is in such an evidence poor environment as X-Risk, including climate change contributions to it. Its pretty interesting that you seem very willing to rely on much more speculative evidence for AI and biorisk (eg probabilistic forecasts which don’t have track records of being able to work well over such long time scales), and I genuinely wonder why this is. Note that such more speculative approaches (in this case superforecasters) gave a 1% probability of climate change being a necessary but not sufficent cause of human extinction by 2100, and gave an even higher probability to global catastrophe by 2100, which certainly then has the probability of later leading to extinction. Whilst I myself am somewhat sceptical of such approaches, I’d be interested in seeing why you seem accepting of them for bio and AI but not climate? Is it because you see evaluation of the existential risk from climate change as a much more evidence rich environment than for bio/AI?
I’m not sure they’re middle of the road on civilisational vulnerability. It would be pretty surprising if extreme weather events made a big difference to the overall picture. For the kinds of extreme weather events one sees in the literature, it’s just not a big influence on global GDP. How bad would a hurricane or flood have to be to push things from ‘counterfactual GDP reduction of 5%’ to civilisational collapse.
I don’t think they fully discount/ignore the possibility of catastrophe 3/4ºC. In part this is just an outcome of the models and of the scientific literature. There are no impacts that come close to catastrophe in the scientific literature for 3/4ºC. I agree they miss some tipping points, but looking at the scientific literature on that, it’s hard to see how it would make a big difference to the overall picture.
I haven’t read those papers and don’t have time to do so now unfortunately. My argument there doesn’t rely on one study but on a range of studies in the literature for different warm periods. The Permian was a very extreme and unusual case because it caused such massive land-based extinctions, which was caused by the release of halogens, which is not relevant to future climate change. Also, both the Permian and PETM were extremely hot relative to what we now seem to be in for (17ºC vs 2.5ºC).
I’m not sure I see how I am not engaging with you on planetary boundaries. I thought we were disagreeing about whether to put weight on planetary boundaries, and I was arguing that the boundaries just seem made up. Using EV may have its own problems but that doesn’t make planetary boundaries valid.
I don’t really see how the world now is more vulnerable to any form of weather events in any respect than it has been at any other point in human history. Society routinely absorbs large bad weather events; they don’t even cause local civilisational collapse any more (in middle and high income countries). Deaths from weather disasters have declined dramatically over the last 100 or so years, which is pretty strong evidence that societal resilience is increasing not decreasing. In the pre-industrial period, all countries suffered turmoil and hunger due to cold and droughts. This doesn’t happen any more in countries that are sufficiently wealthy. Many countries now suffer drought, almost entirely due to implicit subsidies for agricultural water consumption. It is very hard to see how this could lead to eg to collapse in California or Spain.
Can you set out an example of a cascading causal process that would lead to a catastrophe?
I’m not sure that there is some meta-level epistemic disagreement, I think we just disagree about what the evidence says about the impacts of climate change. In 2016, I was much more worried than the average FHI person about climate change, but after looking at the impacts literature and recent changes in likely emissions, I updated towards climate change being a relatively minor risk. Comparing to bio for instance, after reading about trends in gene synthesis technologies and costs, it takes about 30 minutes to see how it poses a major global catastrophic risk in the coming decades. I’ve been researching climate change for six years and struggle to see it. I am not being facetious here, this is my honest take.
I agree that climate-economy models aren’t good at some types of extremes, but I think there are different versions of this argument, some of which have become weaker over the years. One of Weitzman’s points was that there was a decidedly non-negligible chance of more than 6ºC and our economic models weren’t good at capturing how bad this would be and so tended to underestimate climate risk. I think this was basically right at the time he was writing. But since 5ºC now looks less and less likely, this critique has less and less bite. Because there is such a huge literature on the impact of 5ºC, the models now in principle have a much firmer foundation for damage estimates. eg the Takakura 2019 paper that I go on about in the report uses up to date literature on a wide range of impact channels, but still only gets like a 5% counterfactual reduction in welfare-equivalent of GDP by 2100, and so probably higher average living standards than today.
Another version of this is that the models aren’t good at capturing tipping points. I agree with this, but I also find it difficult to see how this would make a dramatic difference to the damage estimates if you actually drill down into the literature on the impact of different tipping points. Tipping points that might cause different levels of warming are not relevant to damage estimates, so the main ones that seem relevant are ice sheet collapse, regional precipitation and temperature changes, such as changes in monsoons, which might be caused eg by collapse of the AMOC. For the impacts discussed in the literature, it is difficult to see how you get anywhere close to an existential catastrophe if any of these things happen.
Aside from that, it is noteworthy that some economic models actually try to capture the literature on the impact of warming of 5ºC on things like agriculture, sea level rise, temperature-related deaths, lost productivity from heat etc. There is a group of scientists who say that 3ºC/4ºC is catastrophic on the basis of what the scientific literature says about these impacts. The models strongly suggest that they are wrong, and it is not clear what their response is.
All this being said, I am sympathetic to some critiques of the economic models, eg a lot of the Nordhaus stuff. When I was writing the report, I had thought about putting no weight on them at all, but after digging a bit I changed my mind. I think some of the models make a decent stab at quantifying aggregate costs.
I agree that climate changes have contributed at least to some civilisational trauma throughout history. The literature on this suggests that climate change has been correlated with local civilisational trauma. But: (a) local collapse is a far cry from global collapse; (b) most of the time this was due to cooling rather than warming; (c) the mechanism was usually damage to agricultural output, but there is now far more slack in the system, and we have massively better technology to deal with any disruption; (d) we in general have far more advanced technology, and whereas in the past >90% of the workforce would have been employed in agriculture, now <20% is (or whatever); (e) the relationship between climate change and civilisational turmoil breaks down by the industrial revolution, which provides some support for point (c).
The paleoclimate point doesn’t rely on one datapoint: it’s data from 160 million years of climatic and evolutionary history. Massive climate change over that period didn’t cause species extinctions, as some might have expect it to have done.
As you say, with climate change, the extinctions usually happened among marine life, due to ocean anoxia and ocean acidification, and it’s hard to see the mechanism by which CO2 pollution would cause land-based extinctions, unless something else weird happens at the time, such as a volcanic eruption puncturing though salt deposits as happened at the Permian.
For the level of warming that now looks likely of 2-4ºC, it’s really hard to see why it would cause similar damage eg to the Permian, given that the effect is an order of magnitude smaller.
I don’t think they are quasi-arbitrary, they are totally arbitrary. eg they propose a planetary boundary for biodiversity intactness which by their own admission is made up. The boundary also can’t be real since various countries across Eurasia completely destroyed their pre-modern ecosystems after the agricultural revolution without causing anything like civilisational collapse.
A lot of people criticise planetary boundaries for being political advocacy. The clearest evidence for this is Steffen et al proposing a supposed planetary boundary for a ‘Hothouse earth’ at 2ºC (which happens to be the Paris target) on the basis of no argument.
When we are acting under uncertainty I think we should use expected value. Alleged boundaries might be a useful schelling point for political negotiation (like the 2ºC threshold), but it’s not a good approach for actually quantifying risk. Another downside of a boundary is that it implies that anything we do once we pass the boundary is pointless.
Kemp, Jehn and others claim that the effect of warming of more than 3ºC is ‘severely neglected’. But all of the impacts literature explores the effect of rcp8.5 by 2100, which implies 4-5ºC of warming. Jehn’s search strategy uses temperature mentions to measure neglect, but if you use RCP mentions, you don’t get the same result.
My argument here was that I think your argument proves too much—it suggests that the world is extremely fragile to eg agricultural disruption and heat waves that happen all the time. Given that the world was eg a lot poorer in 1980 and so had a lot lower adaptive capacity, why didn’t various weather disasters trigger cascading catastrophes back then? The number of people dying in weather-related disasters has declined massively over time, so we should expect the cascade to have happened in the 1920s and less so in the future?
I also don’t see why cascading risk would change the cause ranking among top causes. Why aren’t democratised bioweapons and AI also cascading risks?
What are the causal pathways that might contribute to conflict risk that you think I have missed? I don’t really get what is meant to happen that I haven’t already discussed. I talk about all of the contributors to war outlined in textbooks about war and combine that with the literature on climate impacts. It is just really a stretch to make it an important contributor to US-China dynamics.
Hi John, sorry this has taken a while.
In particular, climate economy models still do bad at the heavy tail, not just of warming, but at civilisational vulnerability etc, again presenting a pretty “middle of the road” rather than heavy tailed distribution. The sort of work from Beard et al 2021 for instance highlights something I think the models pretty profoundly miss. Similarly, I’d be really interested in research similar to Mani et al 2021 on extreme weather events and how this may change due to climate change.
I dpon’t see why the models discount the idea that there is a low but non-negligable probability of catastrophic consequences from 3-4 degrees of warming. What aspect of the models? I’m reticent to rely on things like damage functions here, as they don’t seem to engage with the possib;le heavy-tailedness of damage. Whilst I agree that the models probably are decent approximations of reality, I’m just not really very sure they are useful at telling us anything about the low probabil;ity high impact scenarios that we are worried about here.
Whilst I agree there are reasons to think our vulnerability is less, there is clear reasons to think with a growing interconnected (and potentially fragile) global network and economy, our vulnerability is increasing, meaning that whilst the past collapse data might not be prophetic, there is at least value in it; after all, we are in a very evidence poor environment, meaning that I would be reticent to dismiss it as strongly as you seem to. And whilst it is true our agricultural system is more resilient, there is still a possibility of multiple breadbasket failures etc caused by climate change, and the beard et al and richards et al both explore plausible pathways to this. Again, whilst the past collapse data is definitely not a slam dunk in my favour, I would at least argue it is an update nonetheless. I think you might argue the fact that none led to human extinction makes that data an update in yopur direction, and i think your view on this depends on whether you see collapse and GCR and extinction on a continuum or not; I broadly do, and I assume you broadly don’t?
When I said one data point, I meant really one study. The reason I say this, is as cited, studies of different species/ species groups. In your comment, you don’t seem to engage with Song et al 2021. Kaiho at al 2022 also shows a positive relationship between warming and extinction rate. Moreover, I think it takes an overly confident view of our understanding of kill mechanisms, and seems to suggest that just because we don’t have all what you speculate were the important factors that were present in past mass extinctions doesn’t make that not useful evidence. I think a position like Keller et al 2018 (PETM as the best case, KPg as the worst case) is probably useful at looking at this (only using modern evidence!). Once again, this is an attempt by me, in a low evidence situation, to make best use of the evidence available, and I don’t find your points compelling enough to make me not think that this past precident can’t be informative.
On the Planetary Boundaries, you don’t seem to be engaging with what I’m saying here, which is most alluding to the Baum et al paper on this. Moreover, even if you think we are to use EV, what are you basing the probabilities on? I assume some sort of subjective bayesianism, in which case you’ll have to tell me why I should put a decently high (>1%) prior on moving beyond certain Holocene boundaries posing a genuine threat to humanity? That seems perfectly reasonable to me
I’m not really sure I understand the argument? Whilst in some ways the world has indeed got less vulnerable, in other ways it has got more connected, more economically vulnerable to natural disasters etc. Cascading impact seems to be seen more along these lines than along others. Moreover, if you only had a 5% probability of such a cascade occuring over a century, and we have hardly had a hyper-globalised economy for even that long, why would you expect it to have happened already? Your statements here seem pretty out of step with my actual probabilities etc.. And as I talk about in my talk, I also see problems from AI, biorisk and a whole host more. Thats why this talk, and this approach, is seriously not just about climate change; the hope is to add another approach to studying X-Risk.
I’m also pretty interested in your approach to evidence on X-Risk. I should say from the outset that I think climate change is unlikely to cause a catastrophe, but I don’t think you have provided compelling evidence that the probability is exceptionally small. Your evidence often seems to rely on the very things that we think ought to be suspect in X-Risk scenarios (economic models, continued improved resilience, best case scenario analogies etc.), and you seem to reject some things that might be useful for reasoning in such evidence poor environments (plausibly useful but somewhat flawed historical analogies, foresight, storytelling, scenarios etc.) . Basically, you seem to have a pretty high bar for evidence to be worried about climate change, which whilst I in general think is useful, I’m just not sure how appropriate it is in such an evidence poor environment as X-Risk, including climate change contributions to it. Its pretty interesting that you seem very willing to rely on much more speculative evidence for AI and biorisk (eg probabilistic forecasts which don’t have track records of being able to work well over such long time scales), and I genuinely wonder why this is. Note that such more speculative approaches (in this case superforecasters) gave a 1% probability of climate change being a necessary but not sufficent cause of human extinction by 2100, and gave an even higher probability to global catastrophe by 2100, which certainly then has the probability of later leading to extinction. Whilst I myself am somewhat sceptical of such approaches, I’d be interested in seeing why you seem accepting of them for bio and AI but not climate? Is it because you see evaluation of the existential risk from climate change as a much more evidence rich environment than for bio/AI?
I’m not sure they’re middle of the road on civilisational vulnerability. It would be pretty surprising if extreme weather events made a big difference to the overall picture. For the kinds of extreme weather events one sees in the literature, it’s just not a big influence on global GDP. How bad would a hurricane or flood have to be to push things from ‘counterfactual GDP reduction of 5%’ to civilisational collapse.
I don’t think they fully discount/ignore the possibility of catastrophe 3/4ºC. In part this is just an outcome of the models and of the scientific literature. There are no impacts that come close to catastrophe in the scientific literature for 3/4ºC. I agree they miss some tipping points, but looking at the scientific literature on that, it’s hard to see how it would make a big difference to the overall picture.
I haven’t read those papers and don’t have time to do so now unfortunately. My argument there doesn’t rely on one study but on a range of studies in the literature for different warm periods. The Permian was a very extreme and unusual case because it caused such massive land-based extinctions, which was caused by the release of halogens, which is not relevant to future climate change. Also, both the Permian and PETM were extremely hot relative to what we now seem to be in for (17ºC vs 2.5ºC).
I’m not sure I see how I am not engaging with you on planetary boundaries. I thought we were disagreeing about whether to put weight on planetary boundaries, and I was arguing that the boundaries just seem made up. Using EV may have its own problems but that doesn’t make planetary boundaries valid.
I don’t really see how the world now is more vulnerable to any form of weather events in any respect than it has been at any other point in human history. Society routinely absorbs large bad weather events; they don’t even cause local civilisational collapse any more (in middle and high income countries). Deaths from weather disasters have declined dramatically over the last 100 or so years, which is pretty strong evidence that societal resilience is increasing not decreasing. In the pre-industrial period, all countries suffered turmoil and hunger due to cold and droughts. This doesn’t happen any more in countries that are sufficiently wealthy. Many countries now suffer drought, almost entirely due to implicit subsidies for agricultural water consumption. It is very hard to see how this could lead to eg to collapse in California or Spain.
Can you set out an example of a cascading causal process that would lead to a catastrophe?
I’m not sure that there is some meta-level epistemic disagreement, I think we just disagree about what the evidence says about the impacts of climate change. In 2016, I was much more worried than the average FHI person about climate change, but after looking at the impacts literature and recent changes in likely emissions, I updated towards climate change being a relatively minor risk. Comparing to bio for instance, after reading about trends in gene synthesis technologies and costs, it takes about 30 minutes to see how it poses a major global catastrophic risk in the coming decades. I’ve been researching climate change for six years and struggle to see it. I am not being facetious here, this is my honest take.