Project Drawdown released their 2020 Update last week. It's now completely freely available and, in my opinion, the most accessible quantitative reference on climate solutions.

Updated table of climate solutions:

Drawdown 2020 review (requires email registration to download):

Notably, Reducing food waste has moved up to take the top rank, followed by Health and Education and then Plant-based diets. Refrigerant management, the previous top priority, is now ranked fourth, followed by Tropical forest restoration.

Three out of those five are already front and center in EAs' awareness anyway; but Reducing food waste and Refrigerant management perhaps less so. I'm curious to hear whether this may compel folks to update their mental models (or why not).

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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.

My understanding from looking briefly was that Drawdown focused on total reduction potential, not cost-effectiveness

I think drawdown has lots of flaws as a prioritisation source.

(1) How they arrive at the ranking is unclear - the details on the models at the time I looked were very unclear.

(2) Technologies should be assessed as part of a whole system rather than individually. e.g. Having lots of energy storage makes sense when you have intermittent power sources like solar, but not much when you have controllable ones like gas with carbon capture. So, it doesn't really make sense to assess the possible climate contribution of storage independently of everything else because its contribution depends on the whole system. Figuring out what energy system each country should have depends significantly on local context. e.g solar makes a lot of sense in Australia, but very little in England.

(3) I didn't think that the potential contribution of various different energy technologies was well justified, and provided a false sense of certainty. E.g. nuclear could in principle supply the vast majority of global low carbon energy supply, but you have to think about all the potential unclear political barriers. Solar and wind could provide maybe up to 40% electricity, but you need to think about the massive land use implications of this and the consequent local opposition

(4) They don't talk about neglectedness, which is a crucial determinant of what difference donors can make on the margin. Wind and solar will probably be important going forward, but philanthropists are already ploughing hundreds of millions of dollars into advocating for them in Europe and the US. In contrast, things like CCS and nuclear get almost no money. Even less attention is paid to things like low carbon heavy duty transport.

(5) Some of the research seemed to be lacking in places. e.g. they put refrigerant management very high, but there are strong arguments suggesting that we should deprioritise short-lived climate pollutants. Similar thoughts apply to plant-based diets.

(6)The ranking is from the point of view of governments to a large extent. This isn't a flaw but does make it less relevant for people donating.

There are valid criticisms of Drawdown, but it's lack of consideration of nuclear and research into SMRs is not among them.

*Nuclear energy for electricity production will not make a meaningful contribution to addressing climate change*

I'm happy to go into more technical and numeric detail than the comments below.

1) Nuclear is too expensive (, ( The O&M costs alone (<20% of total cost of a nuclear build) are greater than new onshore wind and utility scale PV. Solar and wind costs have been declining at 5-7% per year, while nuclear costs have stagnated or gone up.

2) SMRs will still involve a rankine-cycle based power production with its massive water and construction requirements. Even if research eventually yields a 10x capital cost reduction in nuclear, by that time it will have to compete with even cheaper wind and solar and new offshore wind and solar perovskites. Simply, advanced nuclear doesn't have a chance at being competitive in the future, even with massive R&D. It's O&M costs will still be above current wind and solar. Most goals involve decarbonizing the electricity sector in developed countries by 2035. It'd be lucky if there were even 1-2 demonstration SMRs online by that time.

3) Variable renewable energy (VRE) is manageable, and grid integration studies from LBNL and NREL show VRE can easily reach 70-80% of production with little additional storage needs. New onshore wind is reaching capacity factors of 40-50%, and offshore wind at 60-70%, creeping into that mythological "baseload" generation. Buildings are becoming much more grid-responsive to control when and how they use power. Energy storage research is getting much more funding and showing similar price declines as early renewables. The challenges are not VRE amount, but rather the power electronics involved with switching from a synchronous-generator based grid to an inverter based grid. Even with current technology, existing energy storage plus overbuild and massive curtailment of VRE will be much cheaper than nuclear in hitting a 100% renewable grid.

The academic debate has moved beyond whether advanced nuclear power will be a relevant solution to addressing climate change. It's now at whether it would be better from a climate perspective to shut down certain LWRs early and spend the money on renewables and efficiency instead, or if a subsidy in the form of a carbon-price would help keep existing LWRs open a little bit longer. This is largely a function of carbon price and utility regulation in mandating that all cost savings from closing nuclear plants go towards efficiency and new VRE.

Instead of seeing nuclear research as promising, we should view it alongside its current R&D partner - CCS for coal plants. Even if it is neglected in total funding compared to other R&D doesn't stop it from being a wasteful money pit. I think there is an argument for SMR R&D for ship propulsion, space propulsion, and extreme security and redundancy military installations, but this is not a climate change consideration.

Hi Matthew,

1. I think you give a partial picture of the split in expert opinion here in the penultimate paragraph. I think it would be more accurate to say that some people take the view you do and some respectable people take the view that firm controllable low carbon power will be very important. e.g. Your headline claim is pretty strongly at odds with IPCC integrated assessment models, which the typical model saying that a quadrupling of nuclear is needed, rather than the controlled mothballing that you suggest here. And these models also assume a massive increase in bioenergy with CCS, which seems very unlikely to happen, suggesting that nuclear will have to step in.

2. The picture you give on cost ignores where most nuclear new build is happening today. The vast majority of new nuclear is built in China at the moment, and the typical plant construction time is around 6 years, with costs at around $3000/kW. This shows that failures in the US and Europe are particular to the politics and licensing regime and to the industry, rather inherent to the technology. And it shows that changing the licensing regime to allow next gen nuclear in the US and Europe could make a large difference.

3. It is useful to think about the role of nuclear as one about reducing the risk of our decarbonisation efforts. On your approach, I take it that we would bet on solar and wind continuing to get cheaper and then taking over 80% of electricity. To me, it is much safer to invest in the full range of low carbon tech options, including nuclear, if there turn out to be barriers to getting to 80% solar and wind.

  • Technology-level levelised cost is a meaningless metric. The more relevant one is the system-level levelised cost. Studies show that once solar and wind go past 50-80% of electricity production, system-level costs start to rise dramatically. Should we bet on the inflection point in the real world being 80% rather than 50% or 40%? I would prefer not to.
  • Cost is only one determinant of political feasibility. The studies you mention I take it refer to increasing long-distance transmission infrastructure 2-4x. The land use requirements of this and of high solar and wind systems are enormous. There is already significant local opposition to onshore wind in the UK, where it supplies about 9% of UK electricity - there was a ban on subsidies until recently even at these levels of penetration. In Germany, new onshore wind has flatlined in part due to local opposition.
  • Value deflation at higher levels seems to be a major problem in high-solar and wind systems. Various studies suggest that for example solar would have to decline well in advance of this historical trend in order to outpace value deflation.
  • The route you propose is the one Germany has taken, and it is going very badly. Why do you think the entire world should double-down on this approach?
  • Historical experience seems like it should carry some weight here. The only advanced economies that have decarbonised are those with lots of hydro and geothermal and/or nuclear power. Nuclear is a proven solution to decarbonised electricity. Solar and wind are not.

4. Your points only focus on electricity. But electricity and heat is only about 45% of emissions from fossil fuel combustion. Nuclear is much better suited to producing zero carbon fuels and district heating than solar and wind.

Responses to your points above:

1. IPCC Integrated Assessment models don't dictate technologies. By design, they assume many different future scenarios and calculate impacts from those scenarios. Some scenarios use ample amounts of BECCS to achieve negative emissions to hit a 2C target by trading off more short term emissions with expensive negative emissions in the future. This isn't a determination of what is needed, just an example of a technology scenario that hits an emissions target. Massive amounts of BECCS would be extremely expensive; IAMs don't factor in these economic factors. However BECCS may be needed to get negative emissions. Nuclear can't do that, and will need to compete economically for energy production. If you think nuclear is absolutely necessary, please send me the particular IAM that states that and the economic assumptions compared to other electric grid build-outs.

When I speak of the academic community here, I'm referring to the community doing resource planning and grid modeling - the people that are making the decisions about what grid resources, transmission, and R&D to pursue. In this community, nuclear is not recognized as a substantial contributor to short term or long term decarbonization.

2. Break out the capital cost figures. Licensing and regulation isn't the major difference. That accounts for less than 10% of the cost; The World Nuclear Association (nuclear lobbying group) puts it at 5% of the cost. The $3k figure in China is because labor is much cheaper there, which is also a reality for renewables.

On cost - I'll make the point again - even with heroic capital cost reductions, nuclear won't be competitive in the market. The O&M and fuel costs associated with rankine-cycle based power production cannot compete with VRE. Even the most nuclear pro lobbying groups can't claim nuclear is competitive using recent data (the link above compares to 2012 prices). Nuclear plants are closing now because even with O&M costs, they are more expensive than new VRE.

The same economics apply to coal plants - large rankine based producers with substantial fuel costs.

The slight difference is that coal also has to contended with large capital expenditures on criteria pollutant emissions controls (in most countries), whereas nuclear has larger capital cost requirements for the reactor.


a) On LCOE vs system LCOE. Marginal LCOE is what determines what new generation resources get built. In fact, utilities have an obligation to consumers to pursue lowest cost generating resources as overseen by the public utility commission. No one uses total system levelized cost in planning, and it's not clear how one would even do that. If this was Sim City and you could plan out the eventually 50 year grid from the beginning could you do it? Maybe, but it may not be centralized generating resources. As for high VRE costs, there isn't "betting" on the cost inflection point for VRE- we have very accurate models of the electric grid and build-out concerns. Electric battery storage is already cost-competitive with gas peakers in some grid regions. And as VRE increases, the marginal LCOE will tilt in favor of load shifting, DR, and storage assets instead of gas peakers, gas CCs, and certainly baseload coal and nuclear plants which have to earn revenue in the production and capacity markets to stay viable.

In a high VRE scenario, it's not clear that added nuclear or any baseload generator is the cost-preferred option to extra VRE with curtailment or even existing storage costs. Saying baseload generators are a solution needs supporting evidence, especially including how the market would need to be restructured to keep these plants viable.

b) On the point of political feasibility - eminent domain is an issue regardless of generating source. Gas lines, transmission lines, siting uranium or coal mines all have political pushback. Local opposition is much stronger against nuclear and fossil generating facilities in general.

c) Value deflation is an issue for solar, though not so much wind with a higher capacity factor and 24/7 power production. This is where load shifting and DR technology in buildings is likely to become cost-competitive with new generation. Building codes in California are already account for this using a TDV (time-dependent valuation) metric in design, rewarding energy savings during peak evening hours a lot and daytime savings comparatively little.

d) Germany heavily subsidized solar, providing the market incentive that brought the price down considerably for everyone else. And now subsidies are no longer needed to make wind and solar competitive - in general, they are the cheapest generating source on their own. But to claim the subsidies failed looking only at historical solar build out in Germany alone in comparison to the total German subsidy cost is to ignore the massive price decrease it meant for solar globally. I could make a similar claim for nuclear if I weighed U.S. nuclear program costs vs. the first 5-10 years of nuclear production in the U.S.

e) Sure, historical experience, especially recent historical experience should carry weight. No advanced economy has decarbonized. The fastest rates of decarbonization in absolute terms are from VRE, and nuclear is nowhere close. France, used as the common example, is building out VRE and retiring older nuclear plants. Nuclear prices have increased in every developed economy in the last 2 decades.

4. Exxon, Shell, BP are very interested in zero carbon fuels. NREL has a $100 million research project on next gen VRE to biofuels "electrons to molecules" funded by Exxon. Here cost of energy is incredibly important; I'm not sure why you suggest nuclear here? Electricity to fuels is well-paired with renewables to absorb low cost solar and wind during periods of otherwise curtailment.

District heating is a specific application where cogeneration is preferable, and a potential U.S. of SMRs in a few major cities with central district steam systems (e.g. NYC). I suspect a cogeneration application is where we most likely see an SMR demonstration project. For newer district systems, there are competing technologies of heat-pump based ambient loops or four-pipe chilled water/hot water loops that are much more efficient than conventional steam district systems and have lower operating costs that steam-based systems.

As to your point that 45% of fossil fuel emissions are electricity and heat? I assume you got that from Fig 2 in:

The numbers heat 2% + combined heat + elec 5% + elec 26% + load following elec 12% + res/commercial heat 10% = 55%, transportation is 22%, cement 4%, iron & steel 5%, and other industry 14%.

Note that this graph includes other industrial non-energy related CO2 emissions and other gas emissions. Cement production involves emissions from limestone reforming in kilns, and steel mills from coke production. Other industry involves substantial methane emissions from refineries and oil and gas production, as well as ammonia.

Combined heat and energy - where future nuclear has potential economic competitive viability is <5% of this picture.

I don't agree with the view that an "all of the above" strategy that includes substantial support for nuclear R&D for electric production is the least risky from a climate perspective. Even if the R&D budget increases, these funds could be better spent on storage, integration, liquid fuels from electricity, direct carbon capture, market commercialization of several lab-proven technologies, or support for better building codes (75% of grid load). I see it as similar to "clean" coal CCS - unlikely to ever be viable and a distraction to less-risky efforts.

Hi Matthew,

Thanks for this vigorous and informed replies!

1. You say that IAM's don't factor in economic factors. I think this is wrong, or perhaps I have misunderstood your point? IAMs model the role of different energy technologies in an energy system meeting an emissions and economic constraint. The typical IAM does indeed imply a quadrupling of nuclear to 2050 (Peters et al, p4). This suggests that you are wrong to give the impression that all experts believe that nuclear should be phased out. As another example, the authors of the Clack et al response to Jacobson et al are all highly respected energy researchers who believe that at least 20% of energy needs to come from firm controllable low carbon sources. This means either gas+ ccs or nuclear, right?

2. It was very difficult until recently for private Gen IV nuclear companies to operate due to licensing and regulation. This was the point I was making.

Korea and UAE also show low cost and labour costs there will be comparable to the US/EU.


a. System levelised cost is important because it tells us what technologies we will need in a completely decarbonised system. It is at the system level where the case for nuclear becomes clear.

Re betting - my point was that there appear to be lots of potential barriers to VRE, including uncertain cost, local opposition, system grid balancing etc. There are a range of studies which suggest that with a zero emissions constraint, costs increase nonlinearly as VRE penetration passes 50%. Do you deny this?

i'm surprised you give the example of batteries to make your case here. A VRE-dependent system has *multi-week* electricity droughts to which batteries are ill-suited. It might be true that we get long duration storage but the technology isn't there yet.

b. The problem I was highlighting was of VRE *relative to* nuclear. VRE at high penetration has colossal land use requirements. David McKay argued that due to local opposition, VRE could at best provide one sixth of electricity in the UK. Nuclear in contrast because it is very energy dense doesn't have the same concerns.

4. I think you are missing my point on Germany. Germany has indeed subsidised VRE a lot and this has indeed helped to bring costs down. However, the point I was making was that Germany's own domestic performance on climate targets is bad relative to Europe, but they are following the exact strategy you propose - no nuclear, lots of VRE. Onshore wind additions fell to a twenty year low last year in part due to local opposition - they are around a quarter of what they need to be for them to get to their target if 65% of electricity from VRE. I think it highly likely that this local opposition to lots of wind will be replicated everywhere else where it is proposed.

5. The fastest rates of decarbonisation in absolute terms are from VRE. I don't think this is right, but perhaps I am not understanding what you mean. France and Sweden nearly completely decarbonised their electricity supply in ten years with nuclear/nuclear+hydro. I don't think anyone is on course to do that with VRE are they?

6. On zero carbon fuels, the problem here is that VRE would mean that the electrolyser is not used most of the time, whereas nuclear could run the electrolyser at max capacity. From memory the electrolyser is a third of the cost of hydrogen production. From modelling I've seen, VRE would be a very expensive way to produce liquid fuels.

I want to make one more point, separated from the disinterested economic and technological arguments above. Understand that lobbying for nuclear research - as you and Let's Fund have promoted - is not politically neutral and does not occur in a vacuum. The U.S. through the DOE and NSF is by far the largest R&D supporter of nuclear and energy research in general, worldwide. The current administration is heavily focusing on financial support and R&D for coal and nuclear at the expense of other energy technologies and energy efficiency. The are using dishonest tactics and misleading information, including some of the points you mentioned above, as talking points to promote these interests. As an example, read the DOE grid reliability report that concluded grids would be fine without coal and nuclear, but had its abstract edited by former DOE head Ricky Perry to claim the opposite result. Two years ago, the administration tried to pass an emergency declaration for subsidies for power production with on-site fuel storage (coal and nuclear). And the most recent main thrust of R&D at DOE is for coal CCS and nuclear. This is at the expense of many other areas of R&D. The current administration has tried multiple times to cut ARPA-E, a highly successful technology development program across the whole energy sector, and the office of energy efficiency and renewable energy (EERE). EERE provides technology R&D and market commercialization for energy efficiency (the cheapest form of energy - "negawatts") and was the source of funding that helped make solar and wind as cheap as they are today. To suggest precious EA dollars go to supporting nuclear R&D in the U.S. is ignorant of the political reality and potentially damaging to other energy and energy efficiency efforts, insofar as it shifts funds instead of increases the pie. I understand this is surely not the intent of Founders Pledge and Let's Fund recommendations. But ignoring this reality is not an excuse for what is, in my opinion, a bad philanthropic recommendation.

Thanks for the link.

Health and Education ... Three out of those five are already front and center in EAs' awareness anyway

According to drawdown Health and Education is mostly about basic education (high school equivalent in USA) and access to contraception. Contraception is a minor issue that EA correctly pays little attention.

Education on the other hand is given very little attention in EA, and is the critical factor in human well being. Sadly a big miss by EA.