Jim Hansen
H simmens
Author of A Climate Vocabulary of the Future
@herbsimmens
HerbSimmens.com
Clive Elsworth
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Alan Kerstein
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Robert Chris
Sent: 17 August 2025 20:51
To: Clive Elsworth <cl...@endorphinsoftware.co.uk>
Cc: H simmens <hsim...@gmail.com>; HPAC <healthy-planet-...@googlegroups.com>; Planetary Restoration <planetary-...@googlegroups.com>
Subject: Re: [HPAC] Jim Hansen
rob...@rtulip.net
Hansen’s rejection of any urgency for sunlight reflection is astonishing in view of his findings about the dominant role of clouds in warming the planet, and the implication that if this feedback is accelerating then it will only get worse, likely quite rapidly. His proposed solution of a carbon fee is both politically impossible and scientifically marginal. Any cooling from such a complicated economic instrument would be rapidly swamped by the heat from darkening.
My other disappointment with the interview was that there was no mention of Hansen’s extraordinary finding that warming from albedo since 2015 is equivalent to a 110 ppm (40 year) increase in CO2 level. As I have mentioned previously, I have asked if this means albedo loss is causing four times as much immediate warming as emissions, but have not seen any comment on this from climate scientists. I would welcome clarification, given that this is a decisive reason to deploy sunlight reflection.
Hansen provided an excellent summary of his findings about clouds in this interview with Dan Miller. I have taken this extract from the transcript, as a very useful way to get up to speed with a central argument in Global Warming in the Pipeline. I include this to help inform discussion of the relative power of albedo and carbon as cooling instruments, noting that nothing we do about carbon can slow the collapse of clouds, which is by far the biggest immediate and tractable cause of warming, and noting that the even larger warming from water vapour can only be reversed if we act on albedo by restoring clouds. The irrelevance of carbon action to cloud warming explains the urgent need for an Albedo Accord. I should also again note that Hansen’s use of total insolation as the denominator for his 0.5% estimate of darkening in this extract is misleading, and was rejected in the recent climate chat with Peter Cox where he rightly used total albedo as the denominator to give a darkening figure of 2.5% this century.
Climate Chat Interview Dan Miller and James Hansen, 17 August 2025, timestamp 25 minutes
DM: one way that you estimated climate sensitivity was using ice age data. But you did it a totally different way as well. you looked at satellite data of the earth radiation balance. How much energy is coming into the earth? How much energy is coming away from the earth? That's the earth energy balance. So tell us how you use that information to also come up with a climate sensitivity.
JH: Yeah, that's really remarkable data measured by the NASA satellite CERES instrument - clouds and earth radiant energy system is what the acronym stands for. But you can measure the changes in the solar energy reflected by the planet and the thermal heat energy emitted by the planet. You can measure those very precisely. Now you can't calibrate them absolutely but we can get the absolute calibration from measurements over a decade or longer with the Argo float data. These several thousand floats are distributed around the world ocean. They're deep diving floats which dive to a depth of two kilometers and then resurface and radio their measurements to a satellite. And so we can measure the changes in the heat content of the ocean. And that's where the energy imbalance of the planet - where the excess energy - must go, is into the ocean. And so that allows a calibration of this earth's energy imbalance. And one thing we learn is that earth's energy imbalance has doubled in the last decade compared to the prior decade. And so that's of course consistent with the global warming acceleration because the ultimate drive for the warming is the planet's energy imbalance. If you've got twice as big an imbalance, you should expect the warming to accelerate. But the other thing is if you just look at the solar reflection, the reflected solar energy, earth has become noticeably darker during the period of satellite data which began in year 2000. The darkening is now half a percent. The albedo of the earth which is about of the order of 29% has decreased by half a percent which is which is a big deal. That's equivalent to two watts per meter squared. It's becoming dark. It has to be becoming darker mainly because of cloud changes.
DM: By the way I should tell so when it gets darker it absorbs more energy from the sun and if it's lighter the albedo is how much it reflects sun away so as it gets darker and these numbers are two watts, I mean you and I once did a calculation this is measured sort of in the range of a million Hiroshima size atomic bombs going off on the earth every single day so the amount of extra energy absorbed from the sun from this darkening is not a tiny bit. It's a crazily large number.
JH: Well, yeah. And the more relevant comparison is to the four watts that causes the global warming of now we estimate 4 1/2° C at equilibrium. So two watts is a big deal. Now that's not a forcing. We would like to know what composes that two watts per meter squared. We know the surface of the planet itself has become a bit darker because the area of sea ice has decreased. Mhm. But we can see exactly where that's occurring and see how much it's contributing to this two watts and it's about 0.15, a fraction of a watt. So most of it is change of albedo due to cloud changes. That's the only thing that's left. Aerosols themselves have become less but their effect is less than a tenth of a watt,the direct effect. So it's mostly cloud changes but that itself could be partly aerosol forcing. aerosols. I mentioned that their forcing is estimated to be between minus1 and minus2 watts per meter squared, but that's mostly from their effect on clouds. They're right.
DM: They form the nuclei for clouds. They make clouds last longer, be brighter, and so it's not the aerosols themselves reflecting the sun very much. It's their impact on clouds that reflect the sun.
JH: Yes. But we had estimated in our first of our long papers that that forcing could be as large as half a watt per meter squared. The people who try to model that with the aerosol cloud microphysics get a smaller number closer to a tenth of a watt per meter squared. But even if it's as large as we estimated, that still leaves more than one watt per meter squared for cloud feedback. And that is of course consistent with large climate sensitivity. If climate sensitivity were only two and a half to three degrees, there would be almost no cloud feedback. But this is telling us that in fact cloud feedback is large and that is another way to come to this conclusion that climate sensitivity is large.
DM: We had George Tselioudis on the program once talking about his study showing how we're getting decreasing clouds in certain places due to the warming and that's a big big climate feedback.
JH: Yeah. George's point is that the question is how does that cloud feedback work and George Tselioudis argues that it's largely a shifting of climate zones which is causing the cloud change but whether it's cloud microphysics it's probably some combination of changes in the cloud microphysics and the shifting of cloud zones but that doesn't affect this conclusion that clouds are an amplifying feedback and climate sensitivity is large.
Regards
Robert Tulip
From: healthy-planet-...@googlegroups.com <healthy-planet-...@googlegroups.com> On Behalf Of Alan Kerstein
Sent: Monday, 18 August 2025 5:52 AM
To: Clive Elsworth <cl...@endorphinsoftware.co.uk>
Cc: H simmens <hsim...@gmail.com>; HPAC <healthy-planet-...@googlegroups.com>; Planetary Restoration <planetary-...@googlegroups.com>
Subject: Re: [HPAC] Jim Hansen
Clive,
H simmens
“”Hansen’s stance has evolved in recent years, particularly as evidence mounts that Earth’s energy imbalance is driving faster temperature rises. In a 2023 paper titled “Global Warming in the Pipeline,” he argued that “temporary solar radiation management (SRM) will probably be needed, e.g., via purposeful injection of atmospheric aerosols,” emphasizing the need to compare the risks of intervention against those of inaction. He reiterated this in public statements, including a Time magazine article where he stated, “We have to recognize we’re geoengineering the planet right now [with greenhouse gasses]… We have to minimize that human-made geoengineering. And, on a temporary timescale, that will probably require reflecting sunlight, just because of how difficult it is to get the greenhouse gasses out of the atmosphere.” He framed this as part of a “Faustian bargain” humanity has made, where past aerosol pollution masked warming but now, as we clean the air for health reasons, the “first Faustian payment is due” in the form of unmasked heating.
More recently, in a February 2025 paper co-authored by Hansen titled “Global Warming Has Accelerated: Are the United Nations and the World Prepared?,” he dedicated a section to “Purposeful Global Cooling,” advocating for SRM research as a way to address temperature overshoot and mitigate risks like Antarctic ice sheet instability and sea level rise. He highlighted methods like stratospheric sulfate injections (citing historical proposals by Mikhail Budyko and Paul Crutzen) and marine cloud brightening via seawater sprays, drawing on the 1991 Mount Pinatubo eruption as a natural analog that temporarily cooled the planet by about 0.3°C. Hansen acknowledges uncertainties and potential downsides, such as impacts on precipitation or ozone, but argues for a “risks vs. risks” evaluation, noting that SRM could recharge ocean circulation and cool depths around Antarctica.
Hansen does not advocate for immediate SRM deployment but stresses the urgency of research, warning that delaying knowledge could mean being “too late” as global temperatures approach +2-3°C, potentially crossing a “point of no return” for irreversible effects like massive sea level rise. He believes informing the public, especially younger generations, about SRM’s potential could heighten pressure to cut emissions rather than create a moral hazard. He also notes stronger public support for SRM in the Global South, where climate vulnerabilities are higher, and calls for international agreements only after decades of further study. This position aligns with his co-signing of a 2023 open letter by over 60 scientists urging accelerated SRM research. Overall, Hansen views SRM as a reluctant but probable necessity in the face of insufficient emissions reductions, while prioritizing long-term decarbonization.
Author of A Climate Vocabulary of the Future
@herbsimmens
On Aug 18, 2025, at 12:23 AM, rob...@rtulip.net wrote:
To view this discussion visit https://groups.google.com/d/msgid/healthy-planet-action-coalition/01fa01dc0ff7%24d2b4df40%24781e9dc0%24%40rtulip.net.
rob...@rtulip.net
Thanks Herb, that past history of support all makes it surprising that he seems to walk this commitment back now in this interview.
The question asked him about both CDR and SRM. He opens by asserting that actions to try to affect the planet's energy balance require prior progress in understanding the ocean and ice sheets, and that he would rather not discuss this in this interview. Then he goes onto CDR before Dan asks him again about SRM.
Surely the best way to understand how the ocean and ice would respond to higher albedo is through field tests of albedo technologies? I don’t see how the sequencing proposed by Hansen here makes any sense. Given the scale of uninformed opposition, the scale of need, the timeframe to impact, and the risks generated by high Earth System Sensitivity, surely pushing toward field research and deployment should be a top climate priority?
Here is the full exchange on geoengineering, starting at one hour fifteen minutes into the recording
Eli: you've previously outlined steps to limit climate impacts that we can take in addition to reducing fossil fuel emissions. What are your thoughts on carbon dioxide removal, taking CO2 out of the atmosphere and on sunlight reflection methods, also known as solar geoengineering?
JH: I'm going to go to a meeting in Finland organized by young people, they're concerned even though they live in a cold country, but they're concerned about the rapid changes that they're beginning to see. And we want to investigate whether there are actions that would make sense to try to affect the planet's energy balance. Well, we before you can answer that question, you need to have some progress in understanding the issues that we were just talking about, about the ocean and the ice sheets, I want to be circumspect about that at the moment. That was what I told Dan. I didn't want to talk about that stuff right now. That's policy.
Of course you would like to be able to take CO2 out of the atmosphere. Nature is actually helping us. The CO2 increase now is only half of the CO2 emissions. So the system is actually taking up CO2 faster than was expected. 20 years ago it was taking up 40%. And even though our emissions have grown a lot and the predictions were that this uptake fraction would decrease. In fact, the uptake fraction has increased. So there may be ways that you can encourage that increase, the uptake to be even larger. I've been involved as a co-author on some of the papers with regard to enhanced weathering, fertilize your fields with rock dust to get them to take up CO2 more effectively, and even with Sophie my oldest grandchild we distributed one ton of biochar on our farm to improve the health of some recently planted trees that were not doing so well. So there are things you can do to remove carbon dioxide from the atmosphere that make good sense for other reasons. I think it doesn't seem economically sensible yet. We haven't found a way to extract it from the air. You could make liquid fuels. If you could extract it from the air and make liquid fuels with it and use those fuels instead of fossil fuels, that would make sense. But as yet, those methods are not economically competitive with fossil fuels. Until you get a carbon price, they're probably not going to be.
DM: any comments on solar geoengineering? You’ve been one of the few climate scientists who said it might be something we need.
JH: Yeah. Well, we're not at the point of recommending that. The focus should be on price on carbon. That's the way you could drive down emissions rapidly and get the natural system to help you draw CO2 out of the atmosphere and you can help the natural system. but as I said I want to be circumc…”
I assume Dan’s respect for Hansen’s request not to discuss this topic led him to then interrupt and end this topic.
Regards
Robert Tulip
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Tom Goreau
Those interested in these crucial issues will want to hear the webinar this Thursday by Brian Soden on potential methods of increasing top of the atmosphere radiation.
Dear colleagues,
Our next biweekly session of the Healthy Planet Action Coalition is on Thursday, August 21st at 5.30 pm Eastern Daylight Time (US).
The Zoom link is our usual one: https://us02web.zoom.us/j/88954851189?pwd=WVZoeTBnN3kyZFoyLzYxZ1JNbDFPUT09
We will be joined by Brian Soden, a former student of Tom Goreau, who will share his reflections on his recent research paper on a potentially more efficient alternative to stratospheric aerosol injection with SO2 or other reflective aerosols.
This method deploys absorptive aerosols like black carbon in the upper stratosphere. Climate models indicate that this new approach can reduce global temperatures an order of magnitude more efficiently per unit aerosol mass than conventional scattering-based interventions.
The abstract of the paper and a link to the full paper is below.
Please feel free to also invite your colleagues and friends to participate.
With best regards,
Dennis Garrity
Steering Circle Coordinator
Healthy Planet Action Coalition
Stratospheric aerosol injection can weaken the carbon dioxide greenhouse effect
https://www.nature.com/articles/s43247-025-02466-z
Communications Earth & Environment volume 6, Article number: 485 (2025)
Abstract
Stratospheric aerosol injection is a proposed method for offsetting greenhouse gas-induced warming by introducing scattering aerosols into the lower stratosphere to reflect sunlight. Here we explore a potentially more efficient alternative: weakening the Earth’s greenhouse effect by deploying absorptive aerosols in the upper stratosphere (~10 hPa). These aerosols warm the carbon dioxide emission level—where outgoing longwave radiation is most sensitive to temperature—thereby enhancing top-of-atmosphere infrared emission without altering atmospheric carbon dioxide concentrations. Idealized climate model simulations indicate that this approach can reduce global temperatures an order of magnitude more efficiently per unit aerosol mass than conventional scattering-based interventions. Although based on simplified model experiments lacking interactive aerosol processes and operational constraints, our results identify a distinct physical mechanism for climate intervention, arguing for further research into the impacts—especially potential unintended side effects—of injecting absorptive aerosols into the upper stratosphere as an alternative solar radiation management strategy.
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