Paul Gambill's climate interventions work — update #3

[Garrity, Dennis]

For your information:

"If you missed the first update back in October, here's the backstory.

The short version of why this matters: we've crossed 1.5°C, tipping points like AMOC collapse could hit within the next decade or two, and neither emissions cuts nor carbon removal will move fast enough to prevent them. Cooling interventions are the only tool that works on the timeline we're facing. But almost nobody is making that case publicly.

That's what we're trying to change. We have a name now: Light The Beacons. The idea is simple: sound the alarm and signal that it's time to take cooling seriously. We're building the cultural permission space for these conversations to actually happen."

From: Paul Gambill <pa...@paulgambill.com>
Date: Saturday, February 28, 2026 at 3:44 AM
To: Dennis Garrity <dennis....@evergreening.org>
Subject: Paul's climate interventions work — update #3

Hey everyone, My last update included my pitch deck for Light The Beacons. The consistent feedback from funders was some version of "we're interested, but demonstrate this at a smaller scale first." There's real alignment on the problem, as the narrative gap around climate interventions is widely recognized. The question is what to do about it. So we're starting with research. We're now getting paid to figure out where narrative strategy can actually expand "permission space" for climate interventions. Through conversations with Joshua Elliott, who leads the ARC program at Renaissance Philanthropy, they funded a three-month pilot to scope out the narrative landscape for climate interventions, figure out where the real permission barriers sit, and develop a coordination strategy for the Climate Emergencies Forum—a network of researchers, funders, and practitioners working on catastrophic climate risks. The contract is signed and we're a month in. I'm co-leading this with Ben Lachman, who spent 20 years building climate, energy, and software products and co-created The Orbital Index, a well-regarded newsletter on the private space industry. He brings a complementary skill set with many years working on energy transition, technical depth, product mindset, and experience communicating complex topics without losing people. What we're doing We picked two risk domains to go deep on: coral reef collapse and Arctic/permafrost destabilization. For each, we're mapping the intervention landscape—who's working on what, who funds it, what's blocked and why—and analyzing where the narrative and permission constraints sit. We're building out an actor and audience map of the broader climate interventions ecosystem, and developing a framework for assessing permission space that coordination bodies like CEF can use going forward. We've been interviewing practitioners, funders, researchers, policy folks, and communications experts across these domains to answer a few core questions through this work: Where do the actual permission barriers sit—is it scientific disagreement, social pressure, institutional inertia, or something else?  How does funding flow in these risk domains, and why does so little of it reach intervention research?  Is there a constituency of people who privately support this work but aren't saying so publicly, and if so, what would change that?  And what can coordination bodies like CEF actually do to shift these dynamics? We have a lot more interviews ahead of us and I don't want to get ahead of the findings. But if any of this resonates with your own experience—or contradicts it—I'd love to hear from you. Where this is heading Ben and I are using this pilot to figure out how we can best move this field forward and make interventions more fundable and actionable. It's clear that the narrative problem is real. There are most definitely social barriers that are holding back work that the science increasingly supports. What's less clear is the best mechanism for solving it. The Stabilization Plan I described in the last update is one possibility, but it might not be the right one. We might need something entirely different. That's part of what we're trying to learn through this research. By May we should have a much clearer picture of what's needed and where we can add the most value. Separately, in January, I published the most complete version yet of how I see the big picture: The Stabilization Framework. If you want to understand why I think we need a third pillar beyond emissions cuts and carbon removal, that's the piece to read. If you're not already subscribed, I publish weekly articles (and a soon-to-come podcast!) on interventions at Inevitable & Obvious. SF Climate Week Part of this pilot work is to do a couple of in-person engagement tests to see what's most effective. To that end, we got invited to co-organize a San Francisco Climate Week event with Devonian Systems on April 21st that's focused on what's needed to stabilize the climate. More details and a registration link coming soon. If you're in the Bay Area or planning to attend SFCW, keep an eye out.  How you can help A couple specific things I'm looking for: People thinking about life in an overshoot world. Researchers, entrepreneurs, or organizations working on what it means to live in a world that's blown past 1.5°C. This could mean adaptation under extreme scenarios, managing tipping point risks, and planning for futures that our current models don't account for. I'm trying to expand my understanding of what's happening at the edges. Big-picture thinkers with audiences. I'm looking for introductions to people like Packy McCormick (Not Boring), or similar newsletter writers, podcast hosts, and commentators who cover large-scale civilizational challenges. Climate interventions should be part of that conversation and largely aren't yet. If you know someone with an audience who thinks about big problems and might be receptive, I'd love an introduction. I'll continue to send more updates as we learn things. Thanks, Paul

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[Alan Kerstein]

Dennis,

This relates to a recent thread about possible ways to get people to feel this like a gut punch. I suggested a way to make this local, personal, and immediate. In regions most susceptible to becoming uninhabitable in the relatively near term, people at the community level can begin contingency planning for evacuation and relocation of the local population in places like Miami and similarly vulnerable cities, low-lying parts of the Baltic region, parts of South Asia, etc. There should be a laser focus on the hazard and the required action, without complicating the picture with immediate mention of preventive measures like SRM that would lead to more abstract discussions that dilute the gut-punch impact. Of course, once people become desperate for a better solution, there could be a low-key explanation of SRM without getting into advocacy mode. The key is to generate enough hullabaloo locally so that it goes viral and gets wider attention.

In general, this or other strategies should involve:

- focusing attention on local impacts that could happen during a relatable time frame

- personalizing the disruption to normal life, e.g. through serious, prudent contingency planning

- informing people about SRM in response to their demand for solutions rather than initiating this part of the discussion

- discussing SRM in an understated way that gives people space to absorb the risk-vs.-risk perspective rather that retreating into absolutism

Alan

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[br...@chesdata.com]

Dennis –

 

I think that Paul’s suggestion that we focus on “stabilization” is good idea.  However, if we want to address “global stabilization” there really is only one intervention that realistically works:

 

(Paul’s suggestion with my comments highlighted in green:)

When I talk about stabilization, I’m trying to capture a range of interventions that share a common purpose: preventing irreversible cascades of compounding catastrophic risks while the slower solutions scale. This could include:

1.       Cooling interventions like stratospheric aerosol injection, marine cloud brightening, and cirrus cloud thinning. Good for global stabilization

2.       Ice sheet preservation using thermosiphons to stabilize glaciers, seabed curtains, and other interventions to slow collapse that’s already underway. Probably not realistic - way too expensive

3.       Ecosystem protection, from localized cooling to protecting coral reefs to interventions that prevent Amazon dieback. Might be helpful for local stabilization, but not something we should count on.  For planning purposes,  I think we should expect that at least 95% of coral reefs will be lost before 2050 no matter what we do.  Preventing Amazon dieback might prevent an additional 0.10 to 0.15⁰C of warming by 2100 – not a particularly large amount  (see below).

4.       Tipping point prevention more broadly, from Arctic preservation, to permafrost management, to other efforts that keep feedback loops from triggering. This is not “stabilization”. This requires that the temperature increase be reduced by mitigation, CDR, cooling interventions, etc.

5.       Regional weather modification and storm intensity reduction, though I know that category is contested and raises its own set of concerns. Not global stabilization

 

Some thoughts:

1. Suggesting that there are realistic ways to address “global stabilization” other than realistic cooling intervention (e.g., mitigation, CDR, new technologies, etc.) gives people false hope that climate change can be “solved” without cooling intervention. 
2. Assume that 0.3–0.5 W/m² of forcing would reduce peak warming by ~0.2–0.3°C.
3. Assume that it would take ten years after a commitment to begin studying the feasibility of implementing stratospheric aerosol injection to reach 0.3–0.5 W/m² of forcing reduction
4. After 10 years it would be possible to start slowly reducing the temperature increase to 1.5°C  (or a lower amount)
5. Assume that, without significant cooling intervention before 2040, the temperature increase in 2040 might be at least 2.0⁰C, with the temperature increasing 0.3-0.4⁰C per decade after 2040.
6. It would be helpful to have climate scientists detail the likely consequences of a both a 1.8⁰C and 2.0⁰C temperature increase in 2040 and a 2.5⁰C temperature increase in 2050
7. It might be helpful to reach a “consensus” on the “maximum acceptable temperature increases” in 2040 and 2050
8. Every 5-year delay in beginning to study the feasibility of implementing stratospheric aerosol injection increases the likely temperature increases in 2040 and 2050 by 0.15-0.2⁰C
9. Given all of the current opposition to cooling intervention, it will take many years (decades?) to convince the public of the need for cooling intervention
10. Our energy might be best spent on coming up with a person/organization/country/group of countries that might be willing to do some initial minimal (and meaningful) deployment of SAI and ”lobbying” them to actually do it

 

Bruce Parker

=====================================================================================

1. The Amazon has turned from a carbon sink to a carbon source

• At the end of the last century the Amazon was sequestering about 0.5 GTCO2 per year (https://link.springer.com/article/10.1186/s13021-016-0069-2). 
• “We estimate that Amazonia carbon emissions increased from a mean of 0.24 ± 0.08 PgC year^-1 in 2010-2018 to 0.44 ± 0.10 PgC year^-1 in 2019 and 0.52 ± 0.10 PgC year^-1 in 2020 (± uncertainty). (https://pubmed.ncbi.nlm.nih.gov/37612502)
• The forest in the south-eastern Amazon has already become a carbon source. This is not just because of emissions from forest fires or deforestation. It is because tree mortality is increasing tremendously. If the Amazon hits a tipping point, our calculations show we are going to lose 50-70% of the forest. That would release between 200 and 250bn tonnes of carbon dioxide between 2050 and 2100, making it completely impossible to limit global warming to 1.5C. (https://www.theguardian.com/environment/ng-interactive/2025/jun/26/tippping-points-amazon-rainforest-climate-scientist-carlos-nobre )
• Future cumulative emissions (from ChatGPT):

Scenario	Cumulative Amazon CO₂ Emissions (to 2100)	Notes	Expected Additional Temperature Increase in 2100 (1⁰C per 1,500 GTCO2 of Cumulative emissions)
Strong mitigation & protection	~40–80 GtCO₂	Based on sustained small net source (–0.16 GtC/yr) plus limited land-use emissions	0.03 to 0.05⁰C
Intermediate (moderate warming, mixed land use)	~100–150 GtCO₂	Accounts for moderate weakening of sink and some forest loss	0.07 to 0.10⁰C
Business-as-usual (high emissions & deforestation)	~200–300+ GtCO₂	Includes potential dieback and large carbon releases (e.g., 250 GtCO₂)	0.13 to >0.20⁰C
Table 1

[Paul Gambill]

Hi Bruce,

Thanks for the detailed feedback. I agree with most of your assumptions and want to build on a couple of points.

You're right that SAI is the only tool that works at a global scale for temperature stabilization. I don't think that's really in dispute. Where I'd push back is on what "stabilization" requires beyond getting the global temperature number down.

Let's say everything goes well: governance challenges get resolved, SAI testing begins in the 2030s, and by the end of that decade we're in full deployment. The serious proposals being discussed today are modest in scope and would ramp up over time. At most, we're plausibly looking at about 1°C of cooling before negative side effects become significant, and initial deployment would start well below that. In the absolute best case, by the late 2030s we've brought temperatures back down to around 1.5°C, maybe a bit lower if atmospheric methane destruction pans out (a very big "if").

That's a world where the tourniquet has been applied to the bleeding wound. But we're not out of the woods. The risks of triggering destabilizing tipping points such as Amazon dieback, ice sheet collapse at Thwaites, and permafrost feedback loops aren't binary thresholds. They're probability ranges that increase the longer we persist even at 1.3–1.5°C. Cooling the global temperature does the bulk of the risk mitigation, no question. But it doesn't eliminate the need to understand and potentially intervene in these specific systems.

And then there's the long-term exit plan of net zero and legacy carbon dioxide removal, which will take hundreds of years. Stabilization doesn't conclude with getting SAI underway.

You may be right that ice sheet preservation is too expensive, or that 95% of coral reefs are lost regardless. But those should be conclusions we reach through funded research, not by default because nobody looked. Ice sheet work has barely been studied. For example, the Arête Glacier Initiative is only now getting started on a 10-year research plan. Proposals for protecting the Amazon beyond stopping deforestation have had essentially zero research. Coral reef interventions have had some, but in the grand scope is actually very little. These are questions with discoverable answers, but they need to be funded, prioritized, and worked on.

Which is why the work I described in the original update is focused on unlocking the barriers to research and philanthropic capital. That's what I see as the highest-leverage tool right now. We don't know if the other interventions will prove viable, but we need to find out.

On your point 10, you're right that finding willing actors is critical. That's essentially the approach several coordinating groups in this space are already pursuing, which is encouraging.

I welcome any further thoughts or areas of disagreement.

Thanks,

Paul

--

Paul Gambill

Inevitable & Obvious

[oswald....@hispeed.ch]

Hi Paul,

 

atmospheric methane destruction is a valid method, it will contribute to global cooling significantly. Unlike SAI it can start on a local scale, it needs no global agreement for initiating it.

 

Discussions in the HPAC community tend to ignore political facts. Of course it has its merits to discuss things “privately”, but facts do not go away by ignoring them.

 

It would be beneficial to discuss avenues to global cooling under the assumption that SAI won’t happen.

 

Regards

 

Oswald Petersen

Author of „GeoRestoration – Cool the Climate with Natural Technology“

Atmospheric Methane Removal AG

Lärchenstr. 5

CH-8280 Kreuzlingen

Tel: +41-71-6887514

Mob: +49-177-2734245

https://amr.earth

https://georestoration.earth

https://cool-planet.earth

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[Michael MacCracken]

Hi Paul--I want to probe a bit about two of your points:

1. Regarding the timetable, especially if we start with high latitude injections where really only needed in times of year with strong sunlight and planes can now get above the tropopause. Aside from governance, why not get started by 2030, given that the rate that climate change seems to be increasing? I'm not at all clear what "testing" will be productive and necessary other than engineering regarding how to do the injection, and testing on that should not really require governance as the amounts to test injection is considerably smaller than existing injections of materials from passenger aircraft, rockets, etc. Yes, there are uncertainties regarding the exact amounts of material to be injected and that ultimately form aerosols, but one can really only work those out by getting started, learning as one goes along and adjusting. The Earth system is not really so sensitive that uncertainties can't be worked out by doing (and some model studies to get plausible ranges) given it can take weeks and more for injected SO2 to form sulfate and there is no way a small, test injection can be followed for that long. The stratification of the stratosphere is going to spread the aerosol out in thin layers that will, in my view, also make it hard to find and sample the injection soon after the injection, especially of a small amount. Basically, I think the general discussion about there being a lot of need for research is overdone and being built up as a way to avoid actually getting started doing it--we have a lot of experience with volcanic eruptions and climate models have been tested against observations on volcanic eruptions and generally do pretty well (injected aerosols cause cooling, mainly in the warm season, which is what is needed). Now, as you note, I agree that better understanding the barriers to doing anything is needed and your note about it being from earlier proposals to change the natural world to try and make it better as Jim Fleming's book discusses may be a key factor, and that, as you say (and I've tried to say over the years), the present situation is the reverse--intervention is intended to keep the climate close to what it would be without GHG emissions. 

2. I'm not clear about the intervention side effects that you are talking about that would be close to the damages from not doing intervention? Many of the model studies making comparisons look at time-averaged impacts being a bit more or less from the time-averaged impacts without intervention. Such a comparison seems quite narrowly conceived. All locations are always facing a range of conditions, some sort of distribution of conditions. It seems to me the comparisons need to be more focused on the ranges of conditions and some sort of measure of how much they overlap or don't and the significance of that situation with respect to the way that the weather and extremes are going to be experienced or not and their resilience to the changes and effects on overall local societal welfare and well-being. Given where climate change without intervention is taking the world, I'm wondering if there are indeed intervention that, as a whole or even locally, would make thoughtful intervention (so on continuing basis using the best, least disruptive approaches) that can be a worse course than without intervention, which it seems to me is the metric to be considering rather than wanting intervention to be, essentially,, perfect.

I'm all for many of the other points you make.

Best, Mike

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[br...@chesdata.com]

Hi Paul -

 

I think we are in general agreement.  Some additional thoughts:

 

1. I think of coral reefs as an “adaptation” issue, not a “stabilization” issue.   And coral reefs are facing three problems – bleaching, ocean acidification, and sea level rise.
2. Sea level rise is also primarily an “adaptation” issue. It might be helpful to have discussions about (1) what the costs of dealing with sea level rise might be (per foot??) between now and 2100 , (2) what amount of sea level rise would be “catastrophic”, and (3) the expected sea level rise this century. 
3. Analysis of cryosphere intervention is fine, but needs to include analysis on what we might be willing to spend on projects. Politicians are reluctant to allocate funds for expensive projects that have little (or no) near-term value for their constituents.  And mobilizing huge amounts of money for global projects will be even more daunting.  SRM might cost $10-$20 billion per year, so should be manageable.  But would projects costing many hundreds of billion dollars be acceptable?  It should be possible to do a “back of the envelope” cost calculation for cryosphere intervention projects, perhaps calculating the cost per foot (or inch?) of sea level rise avoided (and the total a project might capable of)  or cost per tenth of a Watt/square meter of radiative forcing added (and the total RF expected to be added by the project).  Only projects that meet some threshold should be considered (and I doubt that any will)
4. The Amazon is partly a “stabilization” issue.  My analysis in my original email suggested the Amazon is now a carbon source, perhaps a 2 GTCO2/year change from 100 years ago.  If this continues through 2100 cumulative emissions would be about 150 GTCO2, resulting in a temperature increase of a about 0.1°C.  Assuming that SRM is implemented and that CDR costs can be reduced to point CDR can be implemented at scale, the equivalent of Amazonian CO2 emissions can be captured and sequestered
5. Once annual carbon feedback and anthropogenic CO2 emissions get to about 20 GTCO2, the atmospheric CO2 concentration should stabilize.  As emission are reduced below 20 GTCO2 the atmospheric CO2 concentration should decline
6. Humanities biggest challenge is to get the cost of CDR to point CDR can be  (and will be) implemented at scale so that SRM can eventually be ended.  The cost will likely need to be well under $50/ton for removal and storage.  This needs a detailed analysis of the remaining carbon budget, expected anthropogenic CO2 emissions, expected emissions from carbon feedbacks, and what society might realistically be willing to spend for CDR
7.  

Cheers!

 

Bruce  Parker

[Sev Clarke]

Hi Bruce, Paul et al.,

See my comments in bold below.

Cheers,

Sev

On 2 Mar 2026, at 10:28 am, br...@chesdata.com wrote:

Hi Paul -

 

I think we are in general agreement.  Some additional thoughts:

 

1. I think of coral reefs as an “adaptation” issue, not a “stabilization” issue.   And coral reefs are facing three problems – bleaching, ocean acidification, and sea level rise. Most corals should easily adapt to a sea level rise of ~3mm/yr as their vertical growth rate would normally exceed this. However, adaptation is probably not possible for the amount of ocean warming and acidification that is to be expected. Only stabilisation will work. 
2. Sea level rise is also primarily an “adaptation” issue. It might be helpful to have discussions about (1) what the costs of dealing with sea level rise might be (per foot??) between now and 2100 , (2) what amount of sea level rise would be “catastrophic”, and (3) the expected sea level rise this century.  The most viable adaptation method is to move higher, but this involves losing many of our coastal cities, infrastructure and farmland. It would also give us immense refugee, food, conflict and environmental problems. It will be better to use direct cooling methods that help avoid these.
3. Analysis of cryosphere intervention is fine, but needs to include analysis on what we might be willing to spend on projects. Politicians are reluctant to allocate funds for expensive projects that have little (or no) near-term value for their constituents.  And mobilizing huge amounts of money for global projects will be even more daunting.  SRM might cost $10-$20 billion per year, so should be manageable.  But would projects costing many hundreds of billion dollars be acceptable?  It should be possible to do a “back of the envelope” cost calculation for cryosphere intervention projects, perhaps calculating the cost per foot (or inch?) of sea level rise avoided (and the total a project might capable of)  or cost per tenth of a Watt/square meter of radiative forcing added (and the total RF expected to be added by the project).  Only projects that meet some threshold should be considered (and I doubt that any will) Some of the most feasible and economic cryosphere interventions may take place far from cryospheric regions. 
4. The Amazon is partly a “stabilization” issue.  My analysis in my original email suggested the Amazon is now a carbon source, perhaps a 2 GTCO2/year change from 100 years ago.  If this continues through 2100 cumulative emissions would be about 150 GTCO2, resulting in a temperature increase of a about 0.1°C.  Assuming that the better SRM and TRM interventions are implemented and that CDR and/or GGR costs can be reduced to point CDR can be implemented at scale, the equivalent of Amazonian CO2 emissions can be captured and sequestered
5. Once annual carbon feedback and anthropogenic CO2 emissions get to about 20 GTCO2, the atmospheric CO2 concentration should stabilize. No, for stabilisation we need to go net carbon negative for several decades if not centuries. As emission are reduced below 20 GTCO2 the atmospheric CO2 concentration should decline
6. Humanities biggest challenge is to get the cost of CDR to point CDR can be  (and will be) implemented at scale so that SRM can eventually be ended. Not quite. With short and long term increases in albedo and heat radiance from ocean, land and atmospheric surfaces (by direct cooling methods), we and the biosphere could handle considerably higher levels of atmospheric CO2. As good planetary stewards we might well wish to keep on using proven safe SRM and TRM methods.  The cost will likely need to be well under $50/ton for removal and storage.  Some of our proposed CDR methods might well become profitable, that is to say to be of negative cost, once they had been properly optimised and governed. However, this will require substantial investment, persuasion and fortitude. This needs a detailed analysis of the remaining carbon budget, Our carbon budget was probably exceeded in the 1980s. Forget it. Instead, we need to work on finding out which are the best set of climate solutions, then work on deploying them at existential emergency speed. As in wartime, there will be unavoidable costs to such a necessity.  expected anthropogenic CO2 emissions, expected emissions from carbon feedbacks, and what society might realistically be willing to spend for CDR
7.  

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[Gene Fry]

I think the natural CDR rate is about 1 GTCO2 per year, from ordinary rock weathering.

So, on point 5, stabilization should start once emissions fall below 1 GTCO2.

Gene

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[br...@chesdata.com]

Atmospheric CO₂ concentrations will begin to stabilize when total anthropogenic CO₂ emissions are balanced by natural CO₂ sinks. These sinks include the terrestrial biosphere (~11–13 GtCO₂), the oceans (~9–11 GtCO₂), and chemical weathering of rocks (~1–2 GtCO₂). At present, they collectively absorb about 21–26 GtCO₂ per year, roughly half of annual human-caused emissions. Provided that net global emissions remain near 22 gigatons per year, these sinks would likely continue absorbing CO₂ at approximately that rate.

 

Bruce Parker

[Michael MacCracken]

Hi Bruce--The ocean and terrestrial sinks are what the INCREMENTS are now to preindustrial fluxes (when sources and sinks were roughly balance during the Holocene). As emissions go toward zero, there is no guarantee that these rates will continue. Due to wind-mixing of the upper ocean, there is a pretty rapid (year or few) equilibrium of the mixed layer pCO2 and atmospheric CO2--this suggests that the increment to the atmospheric CO2 loading caused each 1-2 years is a key driver of the flux uptake, so if the emissions created difference is reduced, it would seem that the incremental rate of ocean uptake will drop. The additional driver is that the mixed layer loading is being pulled down by the flux to the deep ocean, so contributing to sustaining the atmospheric-mixed layer gradient. With the reduced amount of sea ice formation and deep water formation, how the downward flux will change or be sustained is subject to some discussion.

Similarly for the rate of C uptake by the terrestrial biosphere. FACE (Free-Air Carbon Experiments, I think it is) studies where they doubled the CO2 concentration in envelopes put around plants, etc. suggested that the plant growth would sort of adjust over a few years to the new equilibrium CO2 concentration, so, again, it seems likely that the flux to the terrestrial biosphere is dependent on the ongoing increments to the CO2 concentration by ongoing emissions. If this is indeed the case, then as emissions drop, the terrestrial uptake rate will drop as emissions drop.

Thus, in working toward net zero emissions, it may be that the airborne fraction will tend to be the same and guideline rather than that the fluxes we have now will continue. So, if I understand what you were saying, I think I disagree.

Best, Mike

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[br...@chesdata.com]

Hi Mike –

 

Good points.  I was looking for a simple explanation.

 

To get a better idea of the CO2 sink for various CO2 emissions, I analyzed 12 En-ROADs emissions scenarios with 2100 temperature increases between 1.4 and 4.0⁰C .

 

The graphs shown here indicate that when CO2 emissions are above 20 GTCO2 the atmosphere gains CO2 but when CO2 emissions are below 20 GTCO2 the atmosphere loses CO2. For example, at 440PPM, the CO2 sink is about 25 GTCO2 when CO2 emissions are about 45 GTCO2 and the CO2 sink is about 15 GTCO2 when CO2 emissions are about 10 GTCO2.

 

Bruce Parker

 

(none of the scenarios had emissions of between 10  and 35 GTCO2 when atmospheric CO2 was 430PPM)

[David Price]

Hi Folks

Regarding the terrestrial C budget, I have to agree with Mike but I think you are all underestimating the effect of warmer conditions on the overall effectiveness of natural terrestrial C sinks to continue operating.

There are several contributing factors:

(1) Plant respiration rates and heterotrophic decomposition of dead organic material increase exponentially with mean temperature. The rule of thumb is the so called “Q10 function” which is typically assumed to be about 2 — meaning rates double for every 10 C increase.

(2) Ecosystem shifts, due to their quasi-optimal climate zones shifting (and related to ecological tipping points being crossed), will cause relatively large and rapid accumulations of dead organic material -- more than would occur if the ecosystems are “stable”. There will always be a delay between ecosystem dieback and degradation (along with increased losses of CO2 due to biomass burning, either by humans or natural wildfires), and eventual replacement. E.g., consider the loss of forests to be replaced by shrubs or grasses.

Establishment of “new” stable ecosystems will invariably take longer than the losses of previous ecosystems—and many of these will not be as strong C sinks as the ecosystems that disappear.

(3) Don’t forget high latitude peatlands and organic permafrost. Large areas are thawing and drying out — not only are these prone to accelerated decomposition (see (1) above), they are also quite likely to burn. Hence, their huge potential to release major additional quantities of CO2 and CH4.

These contributing processes are already in progress --- do not assume they will suddenly stop or reverse if GHG concentrations stop increasing. 

Yes FACE experiments showed relatively small changes in C uptake. As I recall what they mainly showed was that photosynthesis rates of ecosystems (including forests) would increase quite significantly in a doubled CO2 atmosphere, (assuming no changes in mean climate and no extra limitations in soil water and nutrients). But this did not result in anything like a proportional increase in net C "sequestered". Plants grew faster, produced more leaves, twigs and branches, fine roots,  and then discarded most of the extra material. This stimulated populations of bacteria, fungi and invertebrates which then decomposed most of the extra material faster as well. 

Regards 

David 

From my cellphone

I acknowledge that I reside on unceded Traditional Territory of the Secwépemc People

On Mar 4, 2026, at 8:36 am, 'Michael MacCracken' via Healthy Planet Action Coalition (HPAC) <healthy-planet-...@googlegroups.com> wrote:



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[robert...@gmail.com]

Interesting details that. as usual, if taken into account would paint a worse picture than the one we already have.  Does anyone know whether, and to what extent, these factors are already built into climate models (whether complex or simple).  If they are already there we can breathe a sigh of relief that things might not be worse than we currently expect.  If they're not, it doesn't matter that much because the story is already beyond bleak without them.  If policymakers aren't acting on what we already know, one has to wonder why they would act if the potential harms were now recognised to be a a notch or two higher on the calamity scale.

The need right now is to provoke an adequate response to what we already know.  Just ramping up the potential grief is probably more of a distraction because it demands investigation and thereby becomes another source of delay.

We have to embrace the uncertainty.  Trying to eliminate it before we act is a recipe for permanent inaction.

Regards

RobertC

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[Michael MacCracken]

Hi Bruce--Very interesting about what EN-ROADS does--I think I'll write and ask them.

Best, Mike

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[robert...@gmail.com]

Hi Bruce

I'm intrigued to understand what you've done here.

You seem to be comparing the CO2 emissions to the CO2 sink.  Is that right?  How did you calculate the sink?  Was that simply the difference between the annual emissions and the annual change in CO2 concentration (expressed in GtCO2)?  Or did you do something more sophisticated to assess the extent to which the atmospheric stock of CO2 affects the sink capacity?  

If you set emissions to zero from 2026, atmospheric concentration immediately starts reducing implying that sinks are taking up the CO2 coming out of the atmosphere.  That's presumably some kind of baseline.

In WTF, if I set annual emissions from 2026 to be a flat 2GtCO2, CO2 ppm comes down to 405ppm by 2100 and then slowly falls to 400ppm by 2300 i.e. more of less flat from 2100.  If I set emissions to zero from 2026 I get 395ppm by 2100 and 373ppm by 2300, i.e. continuing slow decline.  If I set emissions at 5GtCO2, the corresponding ppm are 421 and 451 respectively, i.e. increasing.

I can't get my head round what those results say about sink efficacy, and if they don't say much, what else is needed to be able to complete the picture.

I also don't understand why you selected 12 emissions scenarios by reference to their 2100 warming.  How does the amount of warming affect the sink capacity?

Regards

RobertC

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[John Nissen]

Hi David,

I'm inclined to side with you rather than Bruce.  Absorption/expulsion rates are critically dependent on temperature.  It used to be said that, once 2C was reached, both land and sea sinks would become sources.  I'm not sure this would be true, but you point out several other factors which make things worse.

Cheers, John

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[br...@chesdata.com]

Hi John –

 

My take is that the “climate-related” processes are so complex that we need to rely on output from climate models to give is an idea of what to expect.  (I simply analyzed the result from runs of the EN-ROADs model.)  One of the many failures of the current process is that fails to answer the very question we are addressing here.  What is desperately needed is an analysis similar to mine based on results from the global climate models, including the assumptions that they made.

 

Bruce

[John Nissen]

Fair enough, Bruce.  But I don't trust the models, I'm afraid.  I prefer to work from first principles, and try and get some feel for the magnitude of effects.  An understanding of the operation of the Earth System helps to clarify what's going on.  At least, that's what I claim, somewhat immodestly!  (I did submit a paper to the AGU on the subject.) 

Cheers, John

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[Gene Fry]

I concur with John in not trusting the models.

I suspect their primary problem is they (badly) underestimate cloud feedbacks.

The spread in cloud feedback estimates back in 2017 was huge (-0.2 to +1.2 W/sq m/°C).

Climate scientist Dr. Kate Marvel has highlighted that 

the primary source of variation among different climate models is how they simulate, or "treat," clouds. Because clouds act as both a planetary sunshade (reflecting sunlight) and a greenhouse blanket (trapping heat), slight differences in how models predict future cloud behavior can lead to large discrepancies in predicted future warming.

In recent years, several models in the ICCP6 round have substantially narrowed the gap between climate sensitivity and paleo observations.  In the figure below, cloud feedbacks are in orange.  Mean climate sensitivity is 4.3 for the top group, 3.6 for the earlier group of models in the bottom half

 from Zelinka, 2020

Gene