Climate boundaries and anthropogenic CO2 emissions, CDR and SRM pathways compatible with these boundaries

[Chris Vivian]

All,

 

See this paper behind a paywall:

 

Spaces of anthropogenic CO2 emissions compatible with climate boundaries - https://www.nature.com/articles/s41558-025-02460-5

 

Abstract:

Climate boundaries are planetary boundaries for the climate system: limits within which humanity can sustainably prosper. Here we introduce a modelling framework to analyse global warming, ocean acidification, sea-level rise and Arctic sea-ice melt. Using a reduced-form model, we map out anthropogenic CO2 emissions, carbon dioxide removal and solar radiation management pathways compatible with these boundaries. We define safety levels as the probability to stay within one or several boundaries considering physical uncertainty. If CO2 emissions peak in 2030, net-zero CO2 is reached in 2050, and carbon dioxide removal capacity is 10 PgC yr−1, without solar radiation management, remaining within the global warming boundary of 2 °C exhibits a safety level of 80%. When all four boundaries are considered together, the safety level drops to 35%. Our results highlight key trade-offs in mitigation options and suggest a need to assess climate boundaries holistically to develop sustainable future strategies.

 

Chris.

 

[br...@chesdata.com]

Is there any way to review the data the article used?  The abstract is missing many of assumptions needed to understand how they arrived at their conclusions:

1. “Starting conditions” - temperature increase, CO2 PPM, total RF, albedo, etc., in 2025
2. 2025-2100 by year for
1. Temperature increase, CO2 PPM, total RF
2. Anthropogenic CO2 emissions
3. CO2 removals
4. Carbon feedbacks
5. GHG emissions and RF other than CO2
6. SRM
7. Albedo and Earth’s energy imbalance
8. Etc.

 

Bruce Parker

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[John Nissen]

Hi Chris and Bruce 

The authors disregard the current trend of about 1/3 °C global warming per decade which takes us to 2 °C by 2040. Even if CDR were at 37 GtCO2 per year, cancelling emissions and giving net zero emissions, the warming from legacy emissions would maintain the current warming rate.

How can they be so wrong, and is it a deliberate attempt to mislead us? We see so many articles attempting to justify emissions reduction that I am always suspicious of them. 

Cheers John 

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[John Nissen]

Should we make a complaint to Nature about publishing a misleading paper?

John 

[Chris Vivian]

John,

 

I think you should read the whole paper before making any comments. Someone should be able to access it.

 

Chris.

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[Philip Bogdonoff]

I reached out earlier today to the corresponding author and requested a copy of the paper.  I will forward to the list of I receive it.

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[Stephen Thornhill]

Here’s the paper.

 

I’m new to the group – working in International Development – food security in particular. So just to say thanks for the cutting edge information on the scale of the problems we face.

 

I would be particularly interested in any work that’s being done on the potential impact of different scales of SRM on food production.

 

Best regards

 

Steve

 

Dr Stephen Thornhill

Lecturer and Programme Director of the MSc in Food Security Policy & Management,

Department of Food Business and Development,

Cork University Business School,

University College Cork, Ireland

T +353 (0)21 4903348

M +353 (0)87 2126850

E s.tho...@ucc.ie

 

From: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com> On Behalf Of Philip Bogdonoff
Sent: Monday 1 December 2025 22:54
To: Chris Vivian <chris....@btinternet.com>
Cc: John Nissen <johnnis...@gmail.com>; Bruce Parker <br...@chesdata.com>; healthy-planet-action-coalition <healthy-planet-...@googlegroups.com>
Subject: Re: [HPAC] Climate boundaries and anthropogenic CO2 emissions, CDR and SRM pathways compatible with these boundaries

 

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[Jan Umsonst]

Hi all, a nice example of how the warming goal discussion is loosing contact with reality...

One more temperature jump and we are close to 2°C warming if it's not even breached.

2014-2016 the first temp. Jump with no real decline afterward, 7 years later the next also with no significant cooling afterward.

At the same time CO2 levels breached records by a far marine while ocean heat uptake is at record levels.

I think we can count ourselves lucky if the next temperature jump needs more than 7 years to build up ...

All the best

Jan

--

[John Nissen]

Yes, Jan, 2C is likely around 2040 if warming continues at 1/3 C per decade.  And 2C is one of their four boundaries which must not be crossed according to the Bossy paper.

As for the pre-published paper [1] by Britta Clark (one of David Keith's group I guess), I like the idea of incorporating SRM into the standard impact assessment models, as a policy option.  I wonder whether we could run with this, as a normalisation of the treatment of SRM.

But she has got it wrong about termination shock: a common mistake.  She says:

[Quote]

Of course, both opioids and solar geoengineering come with risks. Solar geoengineering might change local precipitation patterns (Bal et al. 2019), damage the ozone layer (Nowack et al. 2016), and impact plant photosynthesis (Cao 2018). If we deploy the technology over a long enough period, any cessation of solar geoengineering would cause temperatures to rise rapidly to the level they would have reached in the absence of the technology. This risk of ‘termination shock’ has been likened to withdrawals from opioid use. But, the analogy (often implicitly) urges us to think, the potential benefits of solar geoengineering outweigh these risks.

[End quote]

It isn't the temperature which jumps, it is the rate of temperature rise which jumps.  The "addiction" she talks about, by analogy with opioids, is not as serious as she implies.  This is an important part of her argument, since a large number of people are against solar geoengineering because they are worried by it becoming addictive.  Our argument is that SG is essential to avoid catastrophe. The fact that it might have to be applied for many decades is not an argument against it.

Cheers, John

[1] https://philarchive.org/archive/CLASGD-2

Chris has already quoted from the start of this.

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[Bruce Melton -- Austin, Texas]

Thanks for snagging the paper Stephen. I can't help much with food production, though with this work it would seem that IPCC's scenarios would suffice because this work is IPCC scenario-based. This basis is great for the understated consensus, but does not reflect increasingly robust non-consensus work where tipping is the driver of warming targets and mitigation speed. 

When I find a paper with results that are not as recent tipping work suggests, the first thing I do is understand the scenarios of the work, then look for the author's caveats. This following paragraph from their Strengths and Limitations section seems to address their caveats (there may be more in the paper but I limited myself to the first logical explanation of results that are beyond those of the scenarios evaluated.)

"Our results show that assumptions about the level of future
CDR and SRM have a large impact on the space of anthropogenic
activities compatible with climate boundaries, in line with previ -
ous studies 17,29–31 . Our inverse approach requires defining CDR and
SRM as the additional mitigation needed when a floor of positive
emissions or radiative forcing is reached. Because this floor is the
lower bound of the AR6 scenarios envelope 18 (excluding these tech-
nologies), we implicitly assume that all possible mitigation efforts
have been made before resorting to CDR or SRM. This assumption
implies that our results are conservative: if conventional mitigation
cannot deliver as in the AR6 scenarios, the need for CDR or SRM will
be larger than presented here. Similarly, we impose a limit on the rate
of CDR deployment that is based on the fastest decarbonization rate
in AR6 scenarios (approximately −1.5 PgC yr−2 ). The sensibility of our
results (notably the peaking date) to this assumption is illustrated in
Fig. 4b. This constraint is fairly permissive and strengthening it would
markedly reduce the compatible spaces, forcing all pathways to peak
almost immediately."

Steep trails,

MeltOn

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
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Inst...@Bruce.C.Melton
The Band Climate Change
Twitter - BruceCMelton1 

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[Alan Kerstein]

John,

Termination shock is misleading terminology that leads to specious inferences. Whatever the post-termination temperature rise may be, there is a time period during which the temperature is lower than it would have been without the prior SRM deployment. This shows that the benefits of SRM extend beyond termination. This should more properly be called the post-termination bonus. Moreover, this can be reinforced by an estimate of the time-integrated temperature reduction associated with an assumed time-bracketed SRM deployment, expressed in units of years times degrees Centigrade and subdivided into the deployment period and the post-termination period. Is anyone able and willing to set up and evaluate some scenarios?

Alan

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[John Nissen]

Hi Bruce,

IPCC's max CDR of 1.5 pg per year = 1.5 gigatonnes per year.  This is pathetic, put against emissions of 37 GtCO2.  We need around 60 GtCO2 removal per year to be able to phase out SAI by the end of the century.  

To be honest, I don't trust any of the IPCC scenarios and few of the models.  The effect of emissions reduction is always vastly exaggerated.  I look at the heating power to be overcome and the cooling power to overcome that heating power.  Then it becomes obvious that SAI is needed to bring down temperatures in the Arctic and globally.

We certainly need SAI to avoid transgressing the 2C boundary.

Cheers, John

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[Robert Chris]

Hi Alan

I have a termination shock scenario in my presentation.  In some ways I quite like to keep the threat of termination shock alive because I think it's a great counter to the moral hazard argument against SRM.  It goes like this:

Decarbonisation is so radiatively inefficient that it can no longer realistically deliver enough negative forcing quickly enough to avoid COCAWKI.  Ergo, we have to do some SRM because, being constrained by the laws of physics, that's the only other tool available that is sufficiently radiatively efficient to be scaled to deliver enough cooling quickly enough.  But just as relying on no SRM is a high risk strategy, so relying only on SRM will be equally, but perhaps differently, risky.  To manage overall risk from global warming we have to do both decarbonisation and SRM in parallel, both at the quickest rate we can.

Note, that the focus is on the overall risk.  By implication there'll be some trade offs.  One of the biggest political and legal problems that will arise, and may be SRM's nemesis, is that the trade offs imply some redistribution of risks.  That'll make the winners happy, but the losers are likely to resist, and depending upon who they are and how powerful they are, they may do for SRM what the fossil fuel lobby has been so successfully doing to decarbonisation for the last 50 years.  Bear in mind that inescapable uncertainty means that precisely defining the category of losers is impossible, so everyone could reasonably fear being a loser.  That could make the opposition to SRM overwhelming, even if irrationally so.

Regards

Robert

On 06/12/2025 22:39, Alan Kerstein wrote:

Robert,

Since you're soliciting scenarios, here's something I posted on a different thread. It doesn't specify scenarios, but rather a way of reporting the results that might dispel some misconceptions about termination shock, applicable to any pair of scenarios differing only in the inclusion of an SRM deployment interval or omission thereof. I might not be able to connect live to your presentation but I can watch the recording later.

Alan

---------- Forwarded message ---------
From: Alan Kerstein <alan.k...@gmail.com>
Date: Tue, Dec 2, 2025 at 10:11 AM
Subject: Re: [HPAC] Climate boundaries and anthropogenic CO2 emissions, CDR and SRM pathways compatible with these boundaries

[Michael MacCracken]

Hi Robert--

Are you suggesting that the SRM itself that will create loser effects? It seems to me that this is going to be quite hard to really prove as there will still be a dominant GHG effect unless one goes to preindustrial, so the detection and attribution analysis will have to separate out the three components, and with high confidence. I think this will be very hard to do and unlikely that SRM is going to have a dominant effect over both natural variability and the GHG impacts.

And it seems to me that given there seem to be no consequences for GHG increases causing negative impacts, doing so for SRM that will mainly have offsetting effects might well be quite difficult.

Best, Mike

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[oswald....@hispeed.ch]

Hi Robert,

 

GHG removal is the other tool your keep omitting…

 

Have a great Sunday

 

Oswald Petersen

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

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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[Robert Chris]

Hi Mike

I can't see how SRM can't generate loser effects.  For SRM to be effective it has to cool.  The cooling will change average surface temperature but there's no way that I'm aware of that the changes would be Pareto optimal (benefit some, harm no one) because the cooling will be spatially heterogenous, this will cause changes in pressure differentials, this will generate different local weather conditions, these changes will in some cases be inimical to existing local behaviours, people don't like forced change (even though they may later come to benefit from it). 

The fact that things might have been better or worse in some counterfactual scenario is irrelevant because that's not a yardstick that people measure to assess whether they're winners or losers.  They could be losers even in the counterfactual but might they lose more or less?

Your comments endorses the point I was making.  If it's hard to attribute climate effects to their causes, that gives unconstrained scope for doubters to invent all manner of unprovable reasons why anything they don't like is too risky and shouldn't be done.  Manna from heaven for the doubters.  It's a well-proven approach, just raise doubts, the more unprovable the better because if they can't be proved, they almost certainly can't be disproved.  Of course, sanity can sometimes eventually regain the upper hand but not before the lot of unnecessary suffering, but then as much because of that suffering.  The suffering itself becomes instrumental; you need enough to make people more frightened of not acting than of acting.

Did you make your final comment with deliberate irony?  Let me put that to you in a different way.  Do you think that had our predecessors in the 19th century been advised that in a century or so, the accumulation of CO2 emissions might result in COCAWKI, they would have said 'OK then, let's forego all the benefits they might bring along the way and leave all that coal, oil and gas where it has been for the past several tens of millions of years.'  Or might they have said, 'Oh dear!  That's terrible.  Let's impose a tax on all fossil fuel extraction and /or regulations to ensure that the emissions are captured at source.'

Despite all our computing power, epistemologically we're no better placed than they were to make decisions today about SRM.  Those decisions are always going to be based on 'Trust me, I'm a doctor.'  Yeah?  Give me a break!

Until we stop refining the science to see precisely how many angels we can fit on the head of a climate change pin, and start focussing on the rhetoric and communications packages necessary convince those they need to be convinced (quite a big group, but not everyone).  That then has to be coupled with coherent an transparent learn by doing policymaking making.  If we can't know everything before we start, we have to have procedures in place from the start to identify what's working so we can ramp it up, and what's not working so we can amend or abandon it.

We know enough science already!  Things are bad, we must act.  What more do you need to know?  Exactly how dire the situation is, could not be better illustrated than by UNFCCC.  In 1990s this was a timely and radical international policy move.  For three decades it has demonstrably failed to deliver.  What learning has been emerged from this failure?  How has the UNFCCC been adapted to respond to the urgency of its mission?

I don't know how to solve this problem but I do know that it won't be solved by adding more pages to the climate science doorstop book.  Perhaps get more people to grasp the points made by Collingridge in the 1980s and 90s about the then dysfunctional science/policy interface.

Robert

[Michael MacCracken]

Hi Robert--

I don't disagree there may be all sorts of claims.

I think the spatial variability of cooling will depend a lot on approach, more for MCB than for SRM.

I'd also note that actually what cooling will do is tend to reduce the warming due to GHGs, perhaps by different amounts in different places. Your phrasing makes it seem like the natural plus GHG temperature is the norm.

And no, I don't think the 18th and 19th century people should have held back from fossil fuels, but in the 21st century, there is both a lot more understood and much less damaging alternative sources of energy are available.

And on SRM, our experience with what happens after volcanic eruptions would seem to provide some empirical knowledge to draw from, so not just trust me (of course, that does require the public to have some degree of sense). And then the idea is to start small and learn and adjust as we go along. I think it was Reagan who advocated trust but verify.

And as to knowing enough to act, we do have to understand how best to act and if the actions are working as projected. And then there are those who want to have even more confidence in the science than others as different decision frameworks are being used and so there are different degrees of knowledge required to know we have to act. On this issue of the "dysfunctional science/policy interface", it seems to me that helping explain the reasons for the disagreements that occur is worth having be much more often explained, explaining the different perspectives and reasoning that lead to what is then labeled as dysfunctional. In my, perhaps naive, view, there are explainable reasons for their different priorities--and these are not being discussed.

Best, Mike