Hi Johannes, thank for all the detailed thoughts. I think we're probably reaching diminishing marginal returns in debating point by point. I will say that we agree that the Rennert et al projections are too pessimisitic, and difficult far future projections can matter a lot with low discounting. Though I think we will need to agree to disagree on the magnitudes of these changes. 

There is one technical point that I'd like to bring to your attention, though, that I think does critically matter. The Rethink application of a new discount rate is NOT a 0% discount rate. It is a 0% "rate of pure time preference", which is one component of the discount rate.  (I'm going to modify my original post to clarify.) Rethink's calculation is built on calculations from the German Environmental Agency, so I will directly reproduce their explanations for how they did discounting:

"we use the social discount rate developed by Frank Ramsey (Ramsey 1928), which combines the two aspects above: expected consumption growth, weighted by its effect on the marginal utility of consumers, and the pure rate of time preference (PRTP).

In the GIVE model the consumption growth rate is a dependent variable. Therefore, it is not possible to specify the exact discount rate used for the climate costs"

I am not familiar enough with these models to get a good intuition for what discount rate would be, and therefore how much weight will be places on the far future. But as a reference, the Stern Review also used Ramsey discounting and a low (.1% PRTP), and resulted in an overall discount rate of 1.4%. 

All of this to say, I think a simple mental model of "no discounting", and therefore the vast majority of damages being in the far future, is not a good description of the Rethink analysis. 

Thanks Stan. I think this is a concise and reasonable critique- I mostly agree. A few thoughts. 

1. My understanding is the CG recently did an internal calculation of SCC along the lines of the Rethink analysis, but one key difference is that they cut off damages around 2100 (not sure the exact year). This was just to have a like-for-like comparison with other interventions where they project benefits out for a fixed amount of time. They came to a conclusion of an SCC around 700. So if you take $1/ton as a reasonable benchmark for climate you get 700x, which doesn't reach the CG bar but is in the ballpark. If I understand correctly, this CG SCC doesn't include growth effects. So my point is that you don't necessarily need long term and growth effects- with just one I think GDH gets competitive under reasonable assumptions, though perhaps not "winning". (I haven't actually seen this CG SCC analysis, but talked to people there about it. Hopefully it gets made public some day!)
2. For (b) I don't think you need damages past 2200 to be competitive with GHD (especially if you do have endogenous growth effects), but the point is well-taken that you do need long-term effects, up to 2100 and beyond. My personal central estimate is that by 2100 we'll have reached near net-zero, at warming of ~2.5 degrees C. But even though emission stops, the warming will persist for centuries, and therefore has the ability to continue to cause damages (compared to a no or lower-warming counterfactual). Of course adaptation is the wildcard. Will AI-powered growth radically increase resilience such that climate damages will drop to zero even in the face of persistent increased temperatures? I am not as optimistic as you are, but I see your perspective. 
    

Thanks a lot for these thoughts, Tony. I'm not sure I have all the answers, but a few ideas to throw in the mix:

• A lot of what we think of as cost-effective interventions in GHD are on-the-ground, direct-delivery type stuff (bednets, vaccines) that require a lot of logistics and therefore large, sophisticated orgs to manage them. This isn't really true for climate (at least in my opinion) where we are focused more on charging policy, technology, and markets. There are still constraints in org capacity, but they look pretty different.
• The climate philanthropy ecosystem actually has a pretty impressive build-out of various funding vehicles that allow lots of money to move very quickly. For instance, there are big cross-sectoral regrantors like Climateworks, tons of sector and region specific regrantors (Industry Hub, Tara Climate Foundation), and focused research organizations working on specific topics (Carbon2Sea, Reflective). These organizations frequently see their missions as building up capacity in a topic as well as funding it. From someone with an EA-aligned perspective, if you believed that the mission of any of these orgs was super cost-effective, they would provide a vehicle to move lots of money quickly. For instance, Founder's Pledge made a ~23M grant to Deploy/US based on this logic. We at Giving Green have so far shied away from giving to regrantors, since we think that keeping tighter control of our grants allows money to move faster (no middleman), and allows us to really focus on what we think is most impactful. But one could definitely debate that choice, and if lots more money came our way we would certainly revisit this assumption.
• As a grantmaker in climate, I haven't felt the absorptive capacity of the field to be a huge constraint. Sometimes we have said "we really want to fund orgs doing XYZ, but can't find people doing it", but I'd say that's the exception rather than the rule. Maybe if I was moving much larger amounts of money (like GW), I would feel these constraints more strongly.
• I really hope that organizations delivering really cost-effective GHD work can scale to meet the moment, that the OP/GW bar goes back up, and that the headline conclusions of this research are indeed softened. That would be great for the world!

Hey Stephen, we at Giving Green actually started a project looking exactly at this- trying to identify cost-effective interventions and funding opportunities at the nexus of health/livelihoods and climate mitigation. We put the research on pause because of other near-term priorities and some uncertainty over whether there was hunger for this kind of thing among donors. But it's something we hope to pick up again next year. 

Thanks for the comments. 

A couple of quick responses.

1. Regardless of what any individual thinks about the underpinning assumptions and methodology, the Rennert et al (2022) SCC is widely used and “mainstream”. 

It is certainly true that there is high uncertainty around the SCC, and a wide range of estimates. But the Rennert et al (2022) paper is just about as mainstream, “blue-chips” of an estimate as you are going to get, and therefore I think is a reasonable anchor for the Rethink analysis.  

A few data points showing how popular the Rennert et al (2022) analysis is (and the underlying GIVE model plus the probabilistic assumptions on emissions pathways that underpin it):

• This work was used heavily by the  Biden administration’s EPA as part of a comprehensive update of their internal social cost of carbon, and their estimate was ultimately adopted. (detailed EPA report here.)
• The German Environment Agency uses a very similar approach built on Rennert, but applies some different assumptions (lower discount rate, equity weighting), and comes to an estimate of 345 EUR (assuming 1% pure rate of time preference)
• From Opus 5.0: “There is no single consensus number, but there is a fairly clear structure to where the field has landed. Short version: ~$190/tCO₂ (2020 USD, 2% near-term discount rate) is the de facto reference value”

Of course this doesn’t mean the paper or its estimated SCC  is “right”, but I do think it’s a highly defensible reference SCC for Rethink’s analysis. As correctly mentioned by Vasco, there are numerous critiques of the Rennert paper, arguing that a lower SCC is more appropriate. But there are also influential critiques in the other direction. In the post I discussed how incorporating effects on economic growth can lead to much higher SCCs. For instance, a recent paper by Bilal and Kanzig (2026) argue for a much higher SCC of $1200 (even assuming a 2% discount rate). 

1. Despite being “mainstream”, is Rennert et al (2022) unreasonably pessimistic about future outcomes?

If I understand correctly, Rennert et al (2022) use distributions of future states of emissions based on Rafferty et at (2017), which use historical data to assign probability distributions to the different IPCC emissions scenarios. If historical trends are not good predictors of future ones (for instance, due to rapid technological advancement), these estimates could be off. 

Personally I’d agree with Johannes that the Rennert future emissions distributions feel pessimistic, but I would not agree with the modifiers "clearly extremely". I think their mean estimate would fall within one standard deviation from the mean in my personal distribution.

But in any case, one could re-do the analysis with more optimistic distributions. Resources for the Future has a handy calculator that allows one to re-calculate the SCC with different models and different parameters. If we switch from the emissions distribution in Rennert (RFF-SP) and instead move to the more optimistic SSP-2 (which is the closest option to my beliefs, though I’d still be a bit more optimistic), SCC falls by 15%, from 185 to 158. Unfortunately the calculator does not allow us to move the discount rate to zero [edit: actually, we want to move the pure rate of time preference to zero, not the discount rate], which is really what we need to test the sensitivity of the Rethink estimate to different emissions futures. One would need actually re-run the models to calculate exactly, but a 5x wedge feels quite off to me.

Hi David, I agree that this is a huge opportunity. That's why we at Giving Green are building a nascent biodiversity charity evaluator, funded by an anonymous donor in the space. We plan to publicly release our initial strategy report along with "Top Charities" in late February. If any potential biodiversity donors would like to see the reports before then, we can share privately. So stay tuned!

I'm mostly aligned with the Seema's view, though I think it's systematic of a wider problem in which funders pay more than their grantees almost universally. I've experienced at both IDinsight (where I was Chief Economist) and Rethink Priorities (where I'm on the board) a steady drumbeat of top talent going to funders, including GiveWell and Coefficient. I don't believe this happens because of any careful thinking on where talent is best allocated in the sector, but instead because (a) foundations just can pay more because they don't have a binding budget constraint and (b) even if they do have enough money (which they typically don't) nonprofits need to be careful about salaries because top salaries are public on 990 forms and donors will be scared away by large salaries.

When I've spoken with friends at funding orgs and brought up the issue of salary disparity, I've usually heard some version of attempting to align salaries with other foundations or the private sector. But that doesn't address this imbalance between foundations and NGOs/grantees in their space. 

After spending some side on both the donee side as well as the donor side (with Giving Green), my opinion is that giving away money is easier and more fun day-to-day than working for an org where you have to fundraise and/or serve demanding clients. Therefore I don't fundamentally think that donor orgs need to pay more to attract similar level of talent as NGOs. But trying to fix the coordination problem required to shift norms in the sector is likely impossible. 

At Giving Green, we happily provide free consultations for donors in this range who are interested in climate change mitigation. 

Thanks so much for the engagement. We at Giving Green share your concern around some of CATF's activities around carbon capture, though I wouldn't go as far as to say that CATF's work on 45Q is "net harmful". Instead we acknowledge there are tradeoffs from CATF's strategy in this sector that have uncertain overall impacts. We have noted this element as a "Key Uncertainty" in our report. The relevant text is copied at the bottom of this post. 

Our recommendation of CATF was primarily based on our assessment of their work in Shipping/Aviation and Enhanced Geothermal, which were two of our focus areas this year. However, we are not specifically recommending restricted donations for two reasons:

1. We think that CATF is an overall strong organization with many important work streams, all focused on climate change mitigation. In these cases, we have a strong bias toward unrestricted funding, as it allows the greatest flexibility for our recommended organizations. 
2. For an organization like CATF that receives a lot of unrestricted funding, recommending restricted funding can be mostly meaningless, since the organization can always funge a restricted donation with unrestricted money. 
    

From the 'Key Uncertainties' Section of our Deep Dive on CATF

"Advocacy for incentives for power sector CCUS and captured CO2 storage via EOR: CATF’s advocacy for enhancements to the US Section 45Q tax credit included continued eligibility for power sector applications of carbon capture utilization and storage (CCUS). There is concern that the tax incentives may extend the life of US coal and natural gas-fired power plants. One analysis suggests that 45Q could increase the operating years of an otherwise end-of-life coal plant into the 2040s, resulting in at least 6 million metric tons of additional CO2e emissions. CATF claims that it foresees little deployment of CCS in the US power sector but that the plants that use it will help bring down its cost through learning by doing, resulting in accelerated uptake in emerging economies. While Giving Green thinks CCS could be a valuable technology in contexts such as heavy industry or power plants in emerging economies, we share concerns about incentivizing its use for US fossil fuel power plants. In addition, CATF has continued to advocate for the inclusion of enhanced oil recovery (EOR) for storage of captured emissions or atmospheric removals in subsidies such as 45Q. CATF argues that EOR is climate beneficial, that it serves as the primary niche market for scaling capture technologies, and that it can help transition to large-scale saline storage. Others question the need to subsidize it, especially given concerns over environmental justice, the potential to prolong oil extraction, and the involvement of the fossil fuel industry in the trajectory of emerging climate technologies like DAC.

Thanks, super-interesting!

On "We still need a RCT powered for Mortality", someone from GW could confirm, but I heard through the grapevine that they are going to fund Kremer to do a large multi-country RCT powered for mortality to get at these very questions.