Firstly, on the assumption that the direct or indirect global catastrophic risk (defined as killing >10% of the global population or doing equivalent damage) of climate change depends on warming of more than 6 degrees, the global catastrophic risk from climate change is at least an order of magnitude lower than previously thought. If you think 4 degrees of warming would be a global catastrophic risk, then that risk is also considerably lower than previously thought: where once it was the most likely outcome, the chance is now arguably lower than 5%.
I think that the crux between climate pessimists and optimists is, at the moment, mostly about how much damage the effects of 2-4 degrees of warming would cause. This has been a recent development—I feel like I saw a lot more arguments that 6+ degrees of warming would make earth uninhabitable in the past when that seemed more likely, and now I see more arguments that 2-4 degrees of warming could cause way more damage than we think. Mark Lynas in a recent 80k podcast puts it this way when asked about civilisational collapse:
Mark Lynas: Oh, I think… You want to put me on the spot. I would say it has a 30 to 40% chance of happening at three degrees, and a 60% chance of happening at four degrees, and 90% at five degrees, and 97% at six degrees.
Arden Koehler: Okay. Okay. No, I appreciate you being willing to put numbers on this because I feel that’s always really hard, but it’s really helpful.
Mark Lynas: Maybe 10% at two degrees.
These new environmentalist arguments for climate posing a GCR aren’t that we expect to get a lot of warming, but that even really modest amounts of warming, like 2-4 degrees, could be enough to cause terrible famines by reducing global food output suddenly or else knock out key industries in a way that cascades to cause mass deaths and civilisational collapse.
They don’t dispute the basic physical effects of 2-4 degrees of warming, but they think that human civilisation is way more fragile than it appears, such that a modest loss of agricultural productivity and/or a couple of key industries being badly damaged by extreme weather could knock out other industries and so on leading to massive economic damage.
Now, I’ve always been very sceptical of these arguments because they seem to rely on nothing but intuition and go against historical precendent, but also because I thought we had reliable evidence against them—the IPCCs economic models of climate change say that 2 degrees of warming, for example, represents only a few percent in lost economic output.
For example, in 2011, Michael Greenstone and Olivier Deschenes published a paper about climate change and mortality (I studied an earlier version of this paper in a grad school class). Their approach is to measure the effect of temperature on mortality rates in normal times, and use that estimate to predict how a warmer world would affect mortality.
The authors make the obvious and grievous mistake of assuming that climate change affects human mortality only through the direct effects of air temperature — heatstroke, heart attack, freezing, and so on. The word “storm” does not appear in the paper. The word “fire” does not appear in the paper. The word “flood” does not appear in the paper. The authors do mention that climate change might increase disease vectors, but wave this away. Near the end of the paper they write that “it is possible that the incidence of extreme events would increase, and these could affect human health…This study is not equipped to shed light on these issues.”
You don’t say.
The big conceptual mistake here is to assume that whatever economists can easily measure is the sum total of what’s important for the world — that events for which a reliable cost or benefit cannot be easily guessed should simply be ignored in cost-benefit calculations. That is bad science and bad policy advice.
His source for a lot of these criticisms appears to be this (admittedly very clearly biased) paper: https://www.tandfonline.com/doi/full/10.1080/14747731.2020.1807856 by Steve Keen, who seems to be some sort of fringe economist. But I see them repeated by environmentalists a lot. The claim is that the economic models are really wrong and therefore we should expect lots more damage from relatively minor amounts of global warming.
So, if we accept these criticisms of the IPCCs climate economic forecasts (and please let me know if there are good responses to them), then where does that leave us epistemically? It means that the total economic damage caused by e.g. 3 degrees of warming doesn’t have a clear, low, upper bound and that the ‘extreme fragility’ argument doesn’t have strong evidence against it.
However there still isn’t any positive evidence for it either! And it still strikes me as implausible, and against historical precedent for how famines work (plus resource shorages are the sort of problem markets are good at solving).
As far as I can tell, this really is the epistemic situation we’re in with regard to the economic side of climate change forecasting—in the podcast episode with Rob Wiblin and Mark Lynas, they discuss this extreme fragility idea and neither cite climate forecasts to try and assess if modest losses to agricultural productivity would cause massive famines or not—it’s just intuition Vs intuiton
Mark Lynas: So that’s, for me, the main question. And one of the most important studies I think that’s ever been performed on this was a study in the PNAS Journal, which looked at what they called synchronous collapse in breadbaskets around the world. So at the moment, the world still produces enough food every single year very reliably. We’ve never had a major food shortage which has been as a result of harvest failure.
Mark Lynas: So I mean, if the U.S. Corn Belt was knocked out one year, that would have a huge impact on food prices, and have a huge impact on food security, in fact, as a direct result of that. But imagine if it really wasn’t just the U.S. Corn Belt. It was Australia, it was Brazil, and Argentina, it was breadbaskets of Eastern Europe, and the former USSR, all of that added together, then you enter a situation which humanity has never experienced before, and which looks very much like famine.
Robert Wiblin: So when I envisage a situation where there’s a huge food shortfall like that, firstly, I think we’ll probably have some heads up that this is coming ahead of time. You start to notice the warning signs earlier, like food prices going up, and food futures going up. And then I imagine that people would start… Because it’ll be a global emergency much worse than the coronavirus, say. You just start seeing everyone starts paying attention to how the hell can we get more calories produced? And fortunately, unlike 500 years ago, we are in the fortunate situation where most people today aren’t already producing food, and most capital today isn’t already allocated towards producing more food. So there’s potentially a bunch of elasticity there where, if food prices go up tenfold, that a lot more people can go out and try to grow food one way or another. And a lot more capital can be reallocated towards agriculture in order to try to ameliorate the effects.
Robert Wiblin: And you can also imagine, just as everyone in March was trying to figure out how the hell do we solve this COVID problem, everyone’s going to be thinking “How can I store food? How can I avoid consuming food? How can we avoid wasting food? Because every calorie looks precious”. And maybe that sense of our adaptability, or our ability to set our mind to something when there’s a huge disaster and just throw everything at it, perhaps makes me more optimistic that we’ll be able to muddle through, perhaps more than you’re envisaging. Do you have a reaction to that?
Mark Lynas: My reaction is: imagine if Donald Trump is in charge of the response. It’s all very well to have optimistic notions of technological progress and adaptive capacity and things. And yeah, if smart people were running the show, that would no doubt be the most likely outcome. But smart people don’t run the show most of the time, in most places, and people are amenable to hate and fear, and denial and conspiracies, and all of those kinds of things as you’ve seen, even in the very short term challenges of COVID.
My point is that, unlike temperature forecasts, there aren’t any concrete models to support either Rob or Mark’s position. And elsewhere in the article Mark claims this scenario is 10% likely with 2 degrees of warming. If he’s right, butterfly effects of 2 degrees of warming causing civilisational collapse is twice as likely as the 5% chance of 4 degrees of warming cited in this post, and it’s therefore where the majority of the subjective risk comes from.
Regardless, as the physics side of climate change modelling has started to rule out enough warming to directly end civilisation by clear obvious mechanisms, this ‘other climate tail risk’ (i.e. what if the fragility argument is right) seems worth investigating if only to exclude the possibility. I still place a very low weight on these arguments being right, but it’s probably higher than the chance we get 6+ degrees of warming.
Again, this isn’t my area so please let me know if this has all been heavily debunked by climate economists. But currently it seems to me that the main arguments of climate pessimists aren’t addressed by ruling out extreme warming scenarios.
Speaking for me personally and not Johannes. I strongly disagree with the claim that 3,4, 5 or 6 degrees of warming would do anything even remotely close to ending human civilisation or causing civilisational collapse. However, I don’t think this post is the best place to discuss the question of climate impacts. I am working on a large report on that question which will be out next year.
I see—that seems really valuable and also exactly the sort of work I was suggesting (I.e. addressing impact uncertainty as well as temperature uncertainty).
In the meantime, are there any sources you could point me to in support of this position, or which respond to objections to current economic climate models?
Also, is your view that the current Econ models are fundamentally flawed but that the economic damage is still nowhere near catastrophic, or that those models are actually reasonable?
For sources, I would recommend just reading the technical summary of the 2014 IPCC Impacts report. There is no indication there that civilisation will end at 4 degrees.
I think a lot of the economic models are very flawed yes. I think it is more useful to look at the impacts literature and try and make your own mind up from there. But I also think it is instructive that the most pessimistic models suggest that 4 degrees of climate change would leave us with something like a 400% increase in GDP compared to a counterfactual 900% increase without climate change by 2100. There is absolutely no indication from any of the economic literature that civilisational collapse is on the cards, and that is an update, even if the models are bad, which they likely are.
There are a couple of sources which I’d recommend taking a look at.
2015 Climate Change Risk Assessment—particularly worth reading the section which includes the quote “A simple conclusion is that we need to know more about the impacts associated with higher degrees of temperature increase. But in many cases this is difficult. For example, it may be close to impossible to say anything about the changes that could take place in complex dynamic systems, such as ecosystems or atmospheric circulation patterns, as a result of very large changes very far into the future.”
Climate change risk assessment 2021 - conclusion starts out by saying “Unless NDCs are dramatically increased, and policy and delivery mechanisms commensurately revised, many of the climate change impacts described in this paper are likely to be locked in by 2040, and become so severe they go beyond the limits of what nations can adapt to.” Section 4 of this paper considers various cascading systemic risks. These are a big part of what makes predicting the future impacts of climate change so hard.
Agree that these seem like useful links. The drought/food insecurity/instability route to mass death that my original comment discusses is addressed by both reports.
The first says there’s a “10% probability that by 2050 the incidence of drought would have increased by 150%, and the plausible worst case would be an increase of 300% by the latter half of the century”, and notes “the estimated future impacts on agriculture and society depend on changes in exposure to droughts and vulnerability to their effects. This will depend not only on population change, economic growth and the extent of croplands, but also on the degree to which drought mitigation measures (such as forecasting and warning, provision of supplementary water supplies or market interventions) are developed.”
The second seems most concerned about brief, year-long crop failures, as discussed in my original post: “probability of a synchronous, greater than 10 per cent crop failure across all the top four maize producing countries is currently near zero, but this rises to around 6.1 per cent each year in the 2040s. The probability of a synchronous crop failure of this order during the decade of the 2040s is just less than 50 per cent”.
On its own, this wouldn’t get anywhere near a GCR even if it happened. A ~10% drop in the yield of all agriculture, not just Maize, wouldn’t kill a remotely proportionate fraction of humanity, of course. Quick googling leads to a mention of a 40% drop in the availability of wheat in the UK in 1799/1800 (including imports), which led to riots and protests but didn’t cause Black Death levels of mass casualties. (Also, following the paper’s source, a loss of >20% is rated at 0.1% probability per year)
What would its effects be in that case (my original question)? This is where the report uses a combination of expert elicitation and graphical modelling, but can’t assign conditional probabilities to any specific events occurring, just point out possible pathways from non-catastrophic direct impacts to catastrophic consequences such as state collapse.
Yeah the IPCC seems to think that there is a lot of scope to use irrigation to adapt to increasing droughts. in Bangladesh >50% of agricultural land is irrigated and people in the fertile crescent at the dawn of agriculture made extensive use of irrigation. I’m still pretty worried about the potential effects on very poor agrarian countries. But this still falls well short of a GCR on any reasonable projection of future changes in agricultural technology. The effect outlined is more like—maybe the price of one staple crop increases by at most 50%. For example, the right hand pane shows the effect on food prices of climate change—up by on the order of 25% than the counterfactual, depending on the socioeconomic scenario.
Yeah, between the two papers, the Chatham house paper (and the PNAS paper it linked to, which Lynas also referred to in his interview) seemed like it provided a more plausible route to large scale disaster because it described the potential for sudden supply shocks (most plausibly 10-20% losses to the supply of staple crops, if we stay under 4 degrees of warming) that might only last a year or so but also arrive with under a year of warning.
The pessimist argument would be something like: due to the interacting risks and knock-on effects, even though there are mitigations that would deal easily with a supply shock on that scale, like just rapidly increasing irrigation, people won’t adopt them in time if the shock is sudden enough, so lots of regions will have to deal with shortfalls way bigger than 10-20% and have large scale hunger.
This particular paper has been cited several times by different climate pessimists (particularly ones who are most concerned about knock-on effects of small amounts of warming), so I figured it was worth a closer look. To try and get a sense of what a sudden 10-20% yield loss actually looks like, the paper notes ‘climate-induced yield losses of >10% only occur every 15 to 100 y (Table 1). Climate-induced yield losses of >20% are virtually unseen’.
The argument would then have to be ‘Yes the sudden food supply shocks of 10-20% that happened in the 20th century didn’t cause anything close to a GCR, but maybe if we have to deal with one or two each decade, or we hit one at the unprecedented >20% level the systemic shock becomes too big’. Which, again, is basically impossible to judge as an argument.
Also, the report finishes by seemingly agreeing with your perspective on what these risks actually consist of (i.e. just price rises and concerning effects on poorer countries): Our results portend rising instability in global grain trade and international grain prices, affecting especially the ∼800 million people living in extreme poverty who are most vulnerable to food price spikes. They also underscore the urgency of investments in breeding for heat tolerance.
Update: looks like we are getting a test run of sudden loss of supply of a single crop. The Russia-Ukraine war has led to a 33% drop in the global supply of wheat:
Now, I’ve always been very sceptical of these arguments because they seem to rely on nothing but intuition and go against historical precendent
What historical precedent do you have in mind here? The reason my intuitions initially would go in the opposite direction is a case study like invasive species in Australia.
tl;dr is when an ecosystem has evolved holding certain conditions constant (in this case geographical isolation), and that changes fairly rapidly, even a tiny change like a European rabbit can have negative consequences well beyond what was foreseen by the folks who made the change.
I won’t pretend to be an expert on how analogous climate is to this example, but if someone wanted to shift my intuitions, a good way to start would be to convince me that, for some given optimistic economic forecast, the likelihood it has missed significant knock-on negative consequences of an X degree average rise in temperature is <50%.
I think that the crux between climate pessimists and optimists is, at the moment, mostly about how much damage the effects of 2-4 degrees of warming would cause. This has been a recent development—I feel like I saw a lot more arguments that 6+ degrees of warming would make earth uninhabitable in the past when that seemed more likely, and now I see more arguments that 2-4 degrees of warming could cause way more damage than we think. Mark Lynas in a recent 80k podcast puts it this way when asked about civilisational collapse:
These new environmentalist arguments for climate posing a GCR aren’t that we expect to get a lot of warming, but that even really modest amounts of warming, like 2-4 degrees, could be enough to cause terrible famines by reducing global food output suddenly or else knock out key industries in a way that cascades to cause mass deaths and civilisational collapse.
They don’t dispute the basic physical effects of 2-4 degrees of warming, but they think that human civilisation is way more fragile than it appears, such that a modest loss of agricultural productivity and/or a couple of key industries being badly damaged by extreme weather could knock out other industries and so on leading to massive economic damage.
Now, I’ve always been very sceptical of these arguments because they seem to rely on nothing but intuition and go against historical precendent, but also because I thought we had reliable evidence against them—the IPCCs economic models of climate change say that 2 degrees of warming, for example, represents only a few percent in lost economic output.
E.g. this: https://marginalrevolution.com/marginalrevolution/2021/02/the-economic-geography-of-global-warming.html So the damage is bounded and not that high.
However, I found out recently that these models are so oversimplified as to be close to useless—at least according to Noah Smith:
https://noahpinion.substack.com/p/why-has-climate-economics-failed
His source for a lot of these criticisms appears to be this (admittedly very clearly biased) paper: https://www.tandfonline.com/doi/full/10.1080/14747731.2020.1807856 by Steve Keen, who seems to be some sort of fringe economist. But I see them repeated by environmentalists a lot. The claim is that the economic models are really wrong and therefore we should expect lots more damage from relatively minor amounts of global warming.
So, if we accept these criticisms of the IPCCs climate economic forecasts (and please let me know if there are good responses to them), then where does that leave us epistemically? It means that the total economic damage caused by e.g. 3 degrees of warming doesn’t have a clear, low, upper bound and that the ‘extreme fragility’ argument doesn’t have strong evidence against it.
However there still isn’t any positive evidence for it either! And it still strikes me as implausible, and against historical precedent for how famines work (plus resource shorages are the sort of problem markets are good at solving).
As far as I can tell, this really is the epistemic situation we’re in with regard to the economic side of climate change forecasting—in the podcast episode with Rob Wiblin and Mark Lynas, they discuss this extreme fragility idea and neither cite climate forecasts to try and assess if modest losses to agricultural productivity would cause massive famines or not—it’s just intuition Vs intuiton
https://80000hours.org/podcast/episodes/mark-lynas-climate-change-nuclear-energy/?startTime=2614&btp=476595d6
https://80000hours.org/podcast/episodes/mark-lynas-climate-change-nuclear-energy/
My point is that, unlike temperature forecasts, there aren’t any concrete models to support either Rob or Mark’s position. And elsewhere in the article Mark claims this scenario is 10% likely with 2 degrees of warming. If he’s right, butterfly effects of 2 degrees of warming causing civilisational collapse is twice as likely as the 5% chance of 4 degrees of warming cited in this post, and it’s therefore where the majority of the subjective risk comes from.
Regardless, as the physics side of climate change modelling has started to rule out enough warming to directly end civilisation by clear obvious mechanisms, this ‘other climate tail risk’ (i.e. what if the fragility argument is right) seems worth investigating if only to exclude the possibility. I still place a very low weight on these arguments being right, but it’s probably higher than the chance we get 6+ degrees of warming.
Again, this isn’t my area so please let me know if this has all been heavily debunked by climate economists. But currently it seems to me that the main arguments of climate pessimists aren’t addressed by ruling out extreme warming scenarios.
Speaking for me personally and not Johannes. I strongly disagree with the claim that 3,4, 5 or 6 degrees of warming would do anything even remotely close to ending human civilisation or causing civilisational collapse. However, I don’t think this post is the best place to discuss the question of climate impacts. I am working on a large report on that question which will be out next year.
I see—that seems really valuable and also exactly the sort of work I was suggesting (I.e. addressing impact uncertainty as well as temperature uncertainty).
In the meantime, are there any sources you could point me to in support of this position, or which respond to objections to current economic climate models?
Also, is your view that the current Econ models are fundamentally flawed but that the economic damage is still nowhere near catastrophic, or that those models are actually reasonable?
For sources, I would recommend just reading the technical summary of the 2014 IPCC Impacts report. There is no indication there that civilisation will end at 4 degrees.
I think a lot of the economic models are very flawed yes. I think it is more useful to look at the impacts literature and try and make your own mind up from there. But I also think it is instructive that the most pessimistic models suggest that 4 degrees of climate change would leave us with something like a 400% increase in GDP compared to a counterfactual 900% increase without climate change by 2100. There is absolutely no indication from any of the economic literature that civilisational collapse is on the cards, and that is an update, even if the models are bad, which they likely are.
There are a couple of sources which I’d recommend taking a look at.
2015 Climate Change Risk Assessment—particularly worth reading the section which includes the quote “A simple conclusion is that we need to know more about the impacts associated with higher degrees of temperature increase. But in many cases this is difficult. For example, it may be close to impossible to say anything about the changes that could take place in complex dynamic systems, such as ecosystems or atmospheric circulation patterns, as a result of very large changes very far into the future.”
Climate change risk assessment 2021 - conclusion starts out by saying “Unless NDCs are dramatically increased, and policy and delivery mechanisms commensurately revised, many of the climate change impacts described in this paper are likely to be locked in by 2040, and become so severe they go beyond the limits of what nations can adapt to.” Section 4 of this paper considers various cascading systemic risks. These are a big part of what makes predicting the future impacts of climate change so hard.
agree on the first one—it is very good. I hadn’t seen the second one thanks for sharing!
Agree that these seem like useful links. The drought/food insecurity/instability route to mass death that my original comment discusses is addressed by both reports.
The first says there’s a “10% probability that by 2050 the incidence of drought would have increased by 150%, and the plausible worst case would be an increase of 300% by the latter half of the century”, and notes “the estimated future impacts on agriculture and society depend on changes in exposure to droughts and vulnerability to their effects. This will depend not only on population change, economic growth and the extent of croplands, but also on the degree to which drought mitigation measures (such as forecasting and warning, provision of supplementary water supplies or market interventions) are developed.”
The second seems most concerned about brief, year-long crop failures, as discussed in my original post: “probability of a synchronous, greater than 10 per cent crop failure across all the top four maize producing countries is currently near zero, but this rises to around 6.1 per cent each year in the 2040s. The probability of a synchronous crop failure of this order during the decade of the 2040s is just less than 50 per cent”.
On its own, this wouldn’t get anywhere near a GCR even if it happened. A ~10% drop in the yield of all agriculture, not just Maize, wouldn’t kill a remotely proportionate fraction of humanity, of course. Quick googling leads to a mention of a 40% drop in the availability of wheat in the UK in 1799/1800 (including imports), which led to riots and protests but didn’t cause Black Death levels of mass casualties. (Also, following the paper’s source, a loss of >20% is rated at 0.1% probability per year)
What would its effects be in that case (my original question)? This is where the report uses a combination of expert elicitation and graphical modelling, but can’t assign conditional probabilities to any specific events occurring, just point out possible pathways from non-catastrophic direct impacts to catastrophic consequences such as state collapse.
Note that this isn’t a criticism—I’ve worked on a project with the same methodology (graphical modelling based on expert elicitation) assessing the causal pathways towards another potential X-risk that involves many interacting factors. These questions are just really hard, and the Chatham house report is at least explicit about how difficult modelling such interactions is.
Yeah the IPCC seems to think that there is a lot of scope to use irrigation to adapt to increasing droughts. in Bangladesh >50% of agricultural land is irrigated and people in the fertile crescent at the dawn of agriculture made extensive use of irrigation. I’m still pretty worried about the potential effects on very poor agrarian countries. But this still falls well short of a GCR on any reasonable projection of future changes in agricultural technology. The effect outlined is more like—maybe the price of one staple crop increases by at most 50%. For example, the right hand pane shows the effect on food prices of climate change—up by on the order of 25% than the counterfactual, depending on the socioeconomic scenario.
Yeah, between the two papers, the Chatham house paper (and the PNAS paper it linked to, which Lynas also referred to in his interview) seemed like it provided a more plausible route to large scale disaster because it described the potential for sudden supply shocks (most plausibly 10-20% losses to the supply of staple crops, if we stay under 4 degrees of warming) that might only last a year or so but also arrive with under a year of warning.
The pessimist argument would be something like: due to the interacting risks and knock-on effects, even though there are mitigations that would deal easily with a supply shock on that scale, like just rapidly increasing irrigation, people won’t adopt them in time if the shock is sudden enough, so lots of regions will have to deal with shortfalls way bigger than 10-20% and have large scale hunger.
This particular paper has been cited several times by different climate pessimists (particularly ones who are most concerned about knock-on effects of small amounts of warming), so I figured it was worth a closer look. To try and get a sense of what a sudden 10-20% yield loss actually looks like, the paper notes ‘climate-induced yield losses of >10% only occur every 15 to 100 y (Table 1). Climate-induced yield losses of >20% are virtually unseen’.
The argument would then have to be ‘Yes the sudden food supply shocks of 10-20% that happened in the 20th century didn’t cause anything close to a GCR, but maybe if we have to deal with one or two each decade, or we hit one at the unprecedented >20% level the systemic shock becomes too big’. Which, again, is basically impossible to judge as an argument.
Also, the report finishes by seemingly agreeing with your perspective on what these risks actually consist of (i.e. just price rises and concerning effects on poorer countries): Our results portend rising instability in global grain trade and international grain prices, affecting especially the ∼800 million people living in extreme poverty who are most vulnerable to food price spikes. They also underscore the urgency of investments in breeding for heat tolerance.
Update: looks like we are getting a test run of sudden loss of supply of a single crop. The Russia-Ukraine war has led to a 33% drop in the global supply of wheat:
https://www.economist.com/finance-and-economics/2022/03/12/war-in-ukraine-will-cripple-global-food-markets
What historical precedent do you have in mind here? The reason my intuitions initially would go in the opposite direction is a case study like invasive species in Australia.
tl;dr is when an ecosystem has evolved holding certain conditions constant (in this case geographical isolation), and that changes fairly rapidly, even a tiny change like a European rabbit can have negative consequences well beyond what was foreseen by the folks who made the change.
I won’t pretend to be an expert on how analogous climate is to this example, but if someone wanted to shift my intuitions, a good way to start would be to convince me that, for some given optimistic economic forecast, the likelihood it has missed significant knock-on negative consequences of an X degree average rise in temperature is <50%.