Thanks for writing this, this is fascinating!
To me, the assumptions around the issue of risk of loss seem quite optimistic for a couple of reasons:
From these considerations, 1% seems like a realistic guess, but it seems -- at least to me -- unlikely to be conservative in the sense of "with high likelihood being pessimistically biased against the argument".
A related "windows of wisdom" argument would be that ability to act in the future might be especially valuable in times where expropriation takes place / there is a certain turmoil, so investing in non-financial assets that do not require the current market order to persist could be relatively more valuable from that angle.
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.
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
“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!
Thanks -- this is great and very useful, good to have a tractable model of the chain from emissions to warming!A couple of questions, comments, and ideas on the emissions trajectory path of the model, very much in constructive spirit.
Happy to help implement them if you think this would be useful and grateful for any clarifications!
I. What is the meaning of “extra effort” and, relatedly, what can we conclude from this analysis?You write that the model is about constructing a baseline if we do not pursue “extra effort”. It is not quite clear to me what would constitute “extra effort” here, this is not only an issue with your model but with similar attempts as well (e.g. whether RCP 8.5 represents business-as-usual or not). But this seems key for knowing how to use this. From what you write, the main goal is cause prioritization at the current margin, but it seems to me that the emissions trajectory model more closely resembles a worst case that would bound “how bad can it get?”. I will explain through the remainder why I think that. Also, just to clarify, I understand that this is a rough and simple model, though it seems to me that the simplifications tend to upwards-bias the estimate.
II. Carbon intensity assumptions seem closer to worst case than “no extra effort”
The main variable that has past effort flowing into it (assuming we haven’t -- at scale -- foregone growth or kids for climate, which seems really unlikely for the last 30 years) appears to be carbon intensity and this is modeled based on the average trend from the last 30 years (right?). If that is so, then I think there are many reasons to think that this estimate is on the pessimistic side, because:(a) The overarching impact on carbon intensity over the past 30 years has been China’s unprecedented rise in coal consumption, which has weakened the carbon intensity decline due to decoupling in much of the OECD. China is not growing as fast anymore and it does seem, absent the growth shock scenarios via AI or other growth explosions (which you account for separately), rather unlikely that another similarly sized region will experience such strong fossil-driven growth.
(b) For much of the last 30 years, climate policy has not existed in earnest in most parts of the world (The intensity variable goes until 2014, which makes this even more true). This is different now. While climate policy is much weaker than we would like it to be, it is not non-existent anymore.
(c) Relatedly, the last 10 years have seen technological breakthroughs that have not materialized in their impact on carbon intensity yet but that will drive down carbon intensity and that arguably have not been business as usual but rather the result of active climate policy -- primarily, cheap renewables (at least for low levels of penetration) and electric mobility. If one thinks that past carbon intensity trends have mostly been driven by forces other than climate policy, then the existence of climate policy should have an additional effect on carbon intensity (not necessarily emission totals) that we should be able to see going forward.
(d) There are many more of those in store (which we both heavily advocate for :)) that would likely not happen or happen later absent climate concerns, e.g. advanced nuclear, CCS, cheap power-to-gas etc. We would hope those things to happen sooner rather than later, but I don’t think it is right to think that “no extra effort” implies that those things will never happen or that they happen at the same rate and with the same impact on carbon intensity in which they have happened before. [Counterpoint: Long-run low oil prices]
(e) Even if we were to think that there are other “Chinas” in store that would drive up both growth and carbon intensity for a couple of decades, experiences with long-run growth trajectories seem to point towards lower carbon intensity.
III. Worst-case implications of assumed independence
As you write, the assumption of indepence is for simplicity and clearly false, but I do think the effect of this simplification likely leads to a significant over-estimation of climate damage for several reasons:
(a) The independence assumption means that high growth and high carbon intensity over the 21st century is equally likely as low growth and low carbon intensity. But, over such a long time frame, (i) Kuznets curve effects, (ii) affluence-induced postmaterialism and environmental concern, (iii) more low-carbon than high-carbon innovation, (iv) post-industrialization etc. (not fully independent reasons, hinting at the same process) would all seem to suggest that a high growth case would lead to a lower carbon-intensity over the long run, i.e. some moderation that should make the extreme case of high growth and high carbon intensity leading to extreme warming less likely.
I find it hard to think of a substantive relationship between long-run growth and carbon intensity that would make this more likely (but would be good to think about more, maybe I am too positively biased in my expectation here!).(b) I would also think that for the AI-growth scenarios and carbon intensity the relationship between growth and carbon intensity would probably be strongly negative. If everyone gets a lot richer when there are lots of AI-breakthroughs this might push emissions up in total, but at least in terms of intensity a lowering of intensity seems more likely than not (because AI helps with resource efficiency, with innovation and with realizing preferences and most rich people do not enjoy pollution for its own sake, so even if they don’t give up on consumption there will be some positive incentive for resource efficiency and resultant low carbon intensity) [I am more unsure about this point than the other ones](c) Over the time-frame considered, we will be able to observe warming and at least narrow our understanding of climate sensitivity somewhat. As such, assuming that a high-emissions high climate-sensitivity case is as likely as a low-emissions low climate sensitivity case (i.e. assuming independence) seems quite pessimistic, at least when one -- as you tend to suggest (and I agree) -- puts low probability on such abrupt and catastrophic climate change that reaction is impossible.
IV. Other aspects that make this model close to a worst-case
Aside: From what I can tell, the model does not include emissions from land-use, land use change and agriculture. E.g. you write that emissions are 35 GtCO2/year, while with non-energy emissions it is closer to 50Gt/year. Luckily, many of those are short-lived pollutants, so we can somewhat discard them for the present analysis, but forestry and land-use-change seems quite important for mid-range scenarios of climate progress.
(a) As far as I can tell, the model assumes zero negative emissions, while almost all models of successful climate mitigation assume a significant role of negative emissions and there is strongly increasing interest in this space and no fundamental reason to think that all methods of storing carbon will always be expensive. So, this seems fairly pessimistic, especially for those cases of most concern -- assuming high growth, high climate damage and no finding of negative emissions tech seems really unlikely.
(b) The model also assumes zero geo-engineering. But I find it quite hard to imagine a world where we have (i) high growth, (ii) high climate damage and (ii) no geo-engineering (maybe if Russia threatens nuclear war to parties manipulating the climate, but that seems the only case I can think of). I tend to think of geo-engineering as somewhat bounding the badness of climate (and then inviting the potential badness of geo-engineering), what makes you think otherwise?
In any case, great post and looking forward to your thoughts!
I think it is worth treating Drawdown with a couple of grains as salt, in particular it is (a) not neutral but strongly biased to favorite solutions of environmentalists, (b) bases the importance of different solutions on a small set of possible decarbonization futures, (c) focuses only on existing solutions, (d) if useful for EA-style intervention prioritization at all then only as a first step data input, not a conclusion.
(a) is clear from how they discuss nuclear vs. renewables (see Halstead's comment), for example the description of nuclear mentions almost only negatives, whereas the description of wind almost does not mention negative aspects, treats intermittency of wind as if it was a minor issue (whereas it is a major issue as regions seeking to expand renewables experience), does not mention the environmental impacts of materials mining which are higher than for nuclear (given lower energy density) nor the significant opposition to wind power expansion in countries. Then the potential of wind power is assessed at at least 10x that of nuclear by 2050 despite nuclear now contributing more zero-carbon power than wind and not being technologically constrained in any relevant sense. Carbon capture and storage, a key technology in almost all energy decarbonization models (e.g. those featured in IPCC or by the IEA) is not even included in the list!
(b) When we think about decarbonization futures, examining just two scenarios seems way too few for robust planning and investment decisions. When the IPCC or other groups of energy modelers do these kind of analyses they examine hundreds/thousands of futures which then allows to get a sense of the criticality of different technologies (the degree to which they can or cannot be replaced by other technologies and decarbonization outcomes can still be achieved), this tends to raise the importance of technologies where there aren't a multitude of options (such as, for example, zero-carbon fuels for heavy-duty transport and aviation).
(c) The focus of Drawdown is on existing solutions. However, as Hauke Hillebrandt, Halstead and myself have argued in different contexts, energy innovation is hugely neglected and can create very significant leverage by reducing the technology cost (if one had done Drawdown 20 years ago, solar would not have featured, yet the policies focused to advance solar have proven crucial to reduce cost and make solar viable). So, the focus on existing solutions distracts from the importance and potential of accelerating technological innovations. Just two examples where this matters: (i) There is no direct air capture in the list even though advancing direct air capture is plausible one of the most important things one can do right now given the enormous importance of the tech and the relative neglect to date. (ii) There is no advanced nuclear in the list, no accounting for advanced geothermal (mentioned but not modeled), i.e. it is assumed the technological landscape from now to 2050 will be essentially the same though in the last 15 years we got both cheap renewables + fracking, i.e. it seems unrealistic to stay stable for that long.
(d) Relatedly, apart from neglect that is ignored in the analysis (see Halstead's comment for more detail) something else that is ignored here is tractability, how easy these options can be realized. So at best this seems like a list from which to take ideas, but then one needs to look at whether there are effective approaches to realize the potentials and whether those are under-resourced.
I have found Drawdown useful, e.g. it alerted me to the potential of peatlands, but I think we should be careful in putting much faith into it as a last word on climate giving/investment prioritization and rather treat it as one source amongst many.
In my experience the debate about climate damage is quite ideologically loaded so I am a priori very skeptical of using a single study for these kind of estimates, they always come with a host of assumptions that are ultimately fairly arbitrary.
In addition when you have a causal chain of at least three steps (climate sensitivity > impact of warming > human response) each with significant uncertainty that affects the next step it seems easy to get the estimate wrong by much more than one order of magnitude so the strategy of saying 'even if we take a tenth of the estimate' to save us from overestimation does not seem sufficient to me.
Wouldn't you need to look at the price elasticity of egg consumption rather than absolute trends to conclude whether / to which degree the reduced demand by some is moderated by replacement effects?
It also seems that, at least in the medium term, lower prices cannot necessarily support the same scale of egg production so the market would, hopefully, shrink, no?
Thanks, Holden, for the AMA and everyone for their questions!
When looking at the application form initially, there was a mentioning of an applied task as part of the application -- as far as I can tell this has now been removed.
Could someone confirm this change? Does that mean that the application now only consists of the Google Form plus resume in the first stage?
Thanks in advance!