1. Thanks for clarifying the meaning—so it is not a worst case, but more a baseline where extra effort would be going beyond what we currently see.
It still seems to me what you model is significantly more pessimistic than that.
I think average marginal carbon prices are not a good proxy of overall climate policy effort, because carbon prices are usually not the (i) only climate policy, (ii) mostly not the dominant climate policy (possible exceptions of Sweden and British Columbia, but those are both negligible jurisdictions in terms of emissions) and (iii) other much stronger policies exist and drive carbon intensity reductions.
E.g. we both mention renewables, electric mobility and advanced nuclear as (potentially) important influences on carbon intensity trends, yet none of those has been brought about by carbon pricing policies, but by innovation and deployment policy. Across Europe, progressive states in the US, and China, we have fairly aggressive policies to stimulate low-carbon tech, often with implied carbon prices (technology specific and realized via subsidies) in the 100s USD/tCO2 range.
So, I think even without extra effort, there are significant efforts underway to drive cost differentials down, at least for electric power and light-duty transport, and that is very clearly the result of climate policy (plus air pollution policy).
This is far from enough, but I don’t think it is well-proxied by the state of average carbon pricing policy.
2.
a. On China: Yes, the growth factor is in the growth parameter, but it is *also* in the intensity parameter as a weight, in the same period in which China rises quickly by burning lots of coal its economic importance also increases strongly (i.e. its weight in defining the trend).
I would agree that we should expect developing countries to escape poverty as cheaply as possible, though the other aspect there is that the sheer centralized action capacity and population size are anomalous for the Chinese case. Plus, availability and price of natural gas and renewables have somewhat changed since China’s decision to go all the way with coal.
b. Climate policy kicking off: I think we are talking about different things here. Yes, global climate policy is very weak and I would agree with you that we should, for example, not necessarily expect a change in trajectory from the Paris Agreement.
But despite that, strong climate policy exists in some places and will affect carbon intensity once championed technologies do scale. And this is new and this has not been reflected in carbon intensity yet but likely will.
c. Technologies in store: (I actually think the most significant technology for this to date will be electric mobility.) But even if it is solar and wind, I don’t think that “what solar and wind have done in Germany so far” is a good proxy for “what the technologies accelerated by some governments will do worldwide”, because (i) Germany isn’t very sunny, (ii) we phased out nuclear at the same time (genius, I know!), and (iii) we are already experiencing value deflation which most parts of the world will reach significantly later. (iv) Plus, the share of electrification and thereby the impact of low-carbon electric sources will already increase in a “no extra effort” case (v) And we are still in the beginning of seeing the impact of those technologies globally (the data from which you extrapolate the intensity ends in 2014).
d. New technologies in store: CCS and advanced nuclear both might or might not happen and I hope we can make them more likely to happen and happen faster, but at least for Europe and progressive parts of the US carbon prices in the range of USD 50 by 2030 (or comparable non-price policies) are part of my prediction of “no extra effort”. I agree with the relative evaluation of CCS and advanced nuclear.
e. Political coordination: I think both your and my “no extra effort” case assume essentially zero political coordination. When you assume carbon intensity trends going forward based on the last 30 years (and those end in 2014, i.e. pre-Paris), where there was very little coordination on emissions (in the grand scheme of things, Kyoto doesn’t really matter), there being even less coordination might be a plausible worst case, but just assuming continued no coordination should not change the estimate much. Likewise, I think your estimate is pessimistic not because I am more optimistic about global coordination, but because I think you underplay the non-coordinated-but-present efforts by some governments to change relative cost. If they have some effect, then carbon intensity declines in the future should be higher than in the last 30 years as a matter of default no-extra-effort-prediction.
g. Breakdown of cooperation / arms race: I agree with that. That should widen our range of estimates, not sure it should shift the median much (but the mean).
4. Negative emissions: As discussed above, I think also in the no-extra-effort scenario there is significant effort do enable low-carbon tech, and it seems a fairly pessimistic assumption that by the end of the century we will not have at least some cheap negative emissions tech (not necessarily enough to offset all emissions, but significantly more than having no effect in expectation). This is not the world I am seeing when I see what UK, EU, progressive governments in US are doing to further technological development. We are not in a world where no one is trying to make low-carbon solutions succeed and get cheaper. And in particular, it seems hard to imagine a world with high climate sensitivity, high growth and no one attempting to bring down the cost of negative emissions approaches.
This seems quite at odds with typical dynamics of higher problem severity and higher capability driving a more active search for solutions, of which negative emissions are attractive because they can still work after we failed on having foresight early on and avoid some of the more unpredictable risks of geo-engineering.
On geo-engineering: You seem to answer a different question here, the value of geo-engineering. But if the question of the model is, “how hot will it get?”, then I think it makes sense to make an explicit assumption about when you would expect it being used based on empirical expectation.
In terms of conclusion
You write:
“All of this suggests that the estimates of carbon intensity decline might be biased a bit upwards. The most important factors seem to be decline in costs of renewables, electric cars and potentially advanced nuclear, as well as factors e and f.”
I think that downplays the issue and it conflates two distinct effects as if they affected the same variable (carbon intensity), which they do not.
From your list a-d (and g?) are responses to effects on carbon intensity (in my list the points under II).
From your list e-f and the issues under III in my list affect the probability that all four variables driving warming (population, GDP per capita, carbon intensity, climate sensitivity) vary in the same direction with regards to their effect on overall warming probabilities, which is probably less likely (we agree on that) and thereby will have an effect on expected warming quite different from the potential upward bias in carbon intensity.
This latter point is very different from arguing for a mean/median change in carbon intensity decline rate.
As you suggest, I will try to play around with the model a bit and see what the effects of these different assumptions are. Thanks for the good discussion!
2a. On China, I don’t think population size matters for the carbon intensity of gdp—that should mostly be accounted for in the population parameter. agree that gas and reneawables are cheaper and that might be a reason that emerging economies won’t use as much coal.
b. It doesn’t seem to matter that much that strong climate policy exists in some places, e.g. Sweden. What seems to matter is whether there has been a notable change in global climate policy over the last 5 years that renders just extrapolating from the last 30 years especially unreliable. I don’t see anything that would justify that.
c. Yeah that’s fair. renewables a re a reason to think that intensity might decline below trend.
d. The places where we might get $50 per tonne carbon prices are less than 10% of global emissions to 2050, on current trends. historical experience suggests that some extremely wealthy left wing countries might impose high carbon prices in the next 30 years. Unfortunately, this won’t have much of an effect on global emissions. there might be some places that impose high carbon prices, but they will cover a small fraction of emissions, just following the trend of the last 5, 10 or 30 years.
e. I don’t think they assume zero political coordination. Political coordination would increase on the trend it has been doing over the last 5, 10 or 30 years.
4. It might be that there is cheap negative emissions, but this doesn’t seem to me in the most likely range of scenarios (barring ocean fertilisation or something being good, which I don’t know much about). It’s worth pointing out that median carbon intensity ends up being pretty low on the estimate I give—it is a quarter of carbon intensity today, and the the upper end of the 95th percentile is a tenth of carbon intensity today. This is with climate action proceeding at the same dismal pace as it has over the last 30 years.
5. It would be weird to model geoengineering in this model. It seems to make much more sense to think about geoengineering as one of the solution tools you could use given where emissions might go. If you start thinking about the probability of solar geo in this model, the emissions wouldn’t matter anyway, the temperature would. If you think there is a 10% chance of solar geo, then you would have to model at 10% chance of there being 2 degrees of warming. I think it is much easier to think about solar geo separately from this model.
Re 2a, China, what matters is the degree to which it has influenced global average carbon intensity. It is difficult to think of an event as impactful on global average carbon intensity than the boom of the second largest country population wise fueled by coal, at least as long as the estimate of carbon intensity is global (population and gdp/capita matter here as time increasing weights for carbon intensity).
Re 2b, the state of strong local climate policy matters insofar as it gives reason for global carbon intensity decline going forward and the initiatives of California and EU countries on electric mobility and renewables have been very decisive changes begun the past 20 years but with most of their impact in the future.
Re 4, it seems pretty likely to me that we will figure out some negative emissions options that are cheap, there will be strong reasons to try,
there are many natural and technological approaches and there is still time for progress on that. But can’t offer you more than that as justification, I guess I just have a different prior for that.
Re 5, this might be more about semantics then. I agree it would not be natural to build this into the model (though the way you suggest would work) but I also think that for scenarios with more than 2 or 3 degrees of warming expectations about geoengineering will drive a significant part of the answer to your question of how hot it will get.
Hi John,
Thanks for the clarifications and responses!
Regarding your points:
1. Thanks for clarifying the meaning—so it is not a worst case, but more a baseline where extra effort would be going beyond what we currently see.
It still seems to me what you model is significantly more pessimistic than that.
I think average marginal carbon prices are not a good proxy of overall climate policy effort, because carbon prices are usually not the (i) only climate policy, (ii) mostly not the dominant climate policy (possible exceptions of Sweden and British Columbia, but those are both negligible jurisdictions in terms of emissions) and (iii) other much stronger policies exist and drive carbon intensity reductions.
E.g. we both mention renewables, electric mobility and advanced nuclear as (potentially) important influences on carbon intensity trends, yet none of those has been brought about by carbon pricing policies, but by innovation and deployment policy. Across Europe, progressive states in the US, and China, we have fairly aggressive policies to stimulate low-carbon tech, often with implied carbon prices (technology specific and realized via subsidies) in the 100s USD/tCO2 range.
So, I think even without extra effort, there are significant efforts underway to drive cost differentials down, at least for electric power and light-duty transport, and that is very clearly the result of climate policy (plus air pollution policy).
This is far from enough, but I don’t think it is well-proxied by the state of average carbon pricing policy.
2.
a. On China: Yes, the growth factor is in the growth parameter, but it is *also* in the intensity parameter as a weight, in the same period in which China rises quickly by burning lots of coal its economic importance also increases strongly (i.e. its weight in defining the trend).
I would agree that we should expect developing countries to escape poverty as cheaply as possible, though the other aspect there is that the sheer centralized action capacity and population size are anomalous for the Chinese case. Plus, availability and price of natural gas and renewables have somewhat changed since China’s decision to go all the way with coal.
b. Climate policy kicking off: I think we are talking about different things here. Yes, global climate policy is very weak and I would agree with you that we should, for example, not necessarily expect a change in trajectory from the Paris Agreement.
But despite that, strong climate policy exists in some places and will affect carbon intensity once championed technologies do scale. And this is new and this has not been reflected in carbon intensity yet but likely will.
c. Technologies in store: (I actually think the most significant technology for this to date will be electric mobility.) But even if it is solar and wind, I don’t think that “what solar and wind have done in Germany so far” is a good proxy for “what the technologies accelerated by some governments will do worldwide”, because (i) Germany isn’t very sunny, (ii) we phased out nuclear at the same time (genius, I know!), and (iii) we are already experiencing value deflation which most parts of the world will reach significantly later. (iv) Plus, the share of electrification and thereby the impact of low-carbon electric sources will already increase in a “no extra effort” case (v) And we are still in the beginning of seeing the impact of those technologies globally (the data from which you extrapolate the intensity ends in 2014).
d. New technologies in store: CCS and advanced nuclear both might or might not happen and I hope we can make them more likely to happen and happen faster, but at least for Europe and progressive parts of the US carbon prices in the range of USD 50 by 2030 (or comparable non-price policies) are part of my prediction of “no extra effort”. I agree with the relative evaluation of CCS and advanced nuclear.
e. Political coordination: I think both your and my “no extra effort” case assume essentially zero political coordination. When you assume carbon intensity trends going forward based on the last 30 years (and those end in 2014, i.e. pre-Paris), where there was very little coordination on emissions (in the grand scheme of things, Kyoto doesn’t really matter), there being even less coordination might be a plausible worst case, but just assuming continued no coordination should not change the estimate much. Likewise, I think your estimate is pessimistic not because I am more optimistic about global coordination, but because I think you underplay the non-coordinated-but-present efforts by some governments to change relative cost. If they have some effect, then carbon intensity declines in the future should be higher than in the last 30 years as a matter of default no-extra-effort-prediction.
g. Breakdown of cooperation / arms race: I agree with that. That should widen our range of estimates, not sure it should shift the median much (but the mean).
4. Negative emissions: As discussed above, I think also in the no-extra-effort scenario there is significant effort do enable low-carbon tech, and it seems a fairly pessimistic assumption that by the end of the century we will not have at least some cheap negative emissions tech (not necessarily enough to offset all emissions, but significantly more than having no effect in expectation). This is not the world I am seeing when I see what UK, EU, progressive governments in US are doing to further technological development. We are not in a world where no one is trying to make low-carbon solutions succeed and get cheaper.
And in particular, it seems hard to imagine a world with high climate sensitivity, high growth and no one attempting to bring down the cost of negative emissions approaches.
This seems quite at odds with typical dynamics of higher problem severity and higher capability driving a more active search for solutions, of which negative emissions are attractive because they can still work after we failed on having foresight early on and avoid some of the more unpredictable risks of geo-engineering.
On geo-engineering: You seem to answer a different question here, the value of geo-engineering. But if the question of the model is, “how hot will it get?”, then I think it makes sense to make an explicit assumption about when you would expect it being used based on empirical expectation.
In terms of conclusion
You write:
“All of this suggests that the estimates of carbon intensity decline might be biased a bit upwards. The most important factors seem to be decline in costs of renewables, electric cars and potentially advanced nuclear, as well as factors e and f.”
I think that downplays the issue and it conflates two distinct effects as if they affected the same variable (carbon intensity), which they do not.
From your list a-d (and g?) are responses to effects on carbon intensity (in my list the points under II).
From your list e-f and the issues under III in my list affect the probability that all four variables driving warming (population, GDP per capita, carbon intensity, climate sensitivity) vary in the same direction with regards to their effect on overall warming probabilities, which is probably less likely (we agree on that) and thereby will have an effect on expected warming quite different from the potential upward bias in carbon intensity.
This latter point is very different from arguing for a mean/median change in carbon intensity decline rate.
As you suggest, I will try to play around with the model a bit and see what the effects of these different assumptions are. Thanks for the good discussion!
2a. On China, I don’t think population size matters for the carbon intensity of gdp—that should mostly be accounted for in the population parameter. agree that gas and reneawables are cheaper and that might be a reason that emerging economies won’t use as much coal.
b. It doesn’t seem to matter that much that strong climate policy exists in some places, e.g. Sweden. What seems to matter is whether there has been a notable change in global climate policy over the last 5 years that renders just extrapolating from the last 30 years especially unreliable. I don’t see anything that would justify that.
c. Yeah that’s fair. renewables a re a reason to think that intensity might decline below trend.
d. The places where we might get $50 per tonne carbon prices are less than 10% of global emissions to 2050, on current trends. historical experience suggests that some extremely wealthy left wing countries might impose high carbon prices in the next 30 years. Unfortunately, this won’t have much of an effect on global emissions. there might be some places that impose high carbon prices, but they will cover a small fraction of emissions, just following the trend of the last 5, 10 or 30 years.
e. I don’t think they assume zero political coordination. Political coordination would increase on the trend it has been doing over the last 5, 10 or 30 years.
4. It might be that there is cheap negative emissions, but this doesn’t seem to me in the most likely range of scenarios (barring ocean fertilisation or something being good, which I don’t know much about). It’s worth pointing out that median carbon intensity ends up being pretty low on the estimate I give—it is a quarter of carbon intensity today, and the the upper end of the 95th percentile is a tenth of carbon intensity today. This is with climate action proceeding at the same dismal pace as it has over the last 30 years.
5. It would be weird to model geoengineering in this model. It seems to make much more sense to think about geoengineering as one of the solution tools you could use given where emissions might go. If you start thinking about the probability of solar geo in this model, the emissions wouldn’t matter anyway, the temperature would. If you think there is a 10% chance of solar geo, then you would have to model at 10% chance of there being 2 degrees of warming. I think it is much easier to think about solar geo separately from this model.
Re 2a, China, what matters is the degree to which it has influenced global average carbon intensity. It is difficult to think of an event as impactful on global average carbon intensity than the boom of the second largest country population wise fueled by coal, at least as long as the estimate of carbon intensity is global (population and gdp/capita matter here as time increasing weights for carbon intensity).
Re 2b, the state of strong local climate policy matters insofar as it gives reason for global carbon intensity decline going forward and the initiatives of California and EU countries on electric mobility and renewables have been very decisive changes begun the past 20 years but with most of their impact in the future.
Re 4, it seems pretty likely to me that we will figure out some negative emissions options that are cheap, there will be strong reasons to try, there are many natural and technological approaches and there is still time for progress on that. But can’t offer you more than that as justification, I guess I just have a different prior for that.
Re 5, this might be more about semantics then. I agree it would not be natural to build this into the model (though the way you suggest would work) but I also think that for scenarios with more than 2 or 3 degrees of warming expectations about geoengineering will drive a significant part of the answer to your question of how hot it will get.