Solar Geoengineering Likely up to 14 Times More Efficient than CDR: Albedo Misrepresentations in Climate Forcing and Governance - Preprint

[Geoengineering News]

https://www.researchgate.net/publication/394470822_Solar_Geoengineering_Likely_up_to_14_Times_More_Efficient_than_CDR_Albedo_Misrepresentations_in_Climate_Forcing_and_Governance

Authors: Alec Feinberg

August 2025

Abstrct

This study introduces a steady-state, physics-based Unsaturated Linear Forcing (ULF) model that treats each added unit of greenhouse gas (GHG) as having equal thermodynamic forcing potential. By assuming linear amplification within the natural GHG system, the ULF framework provides first-order, feedback-free forcing estimates. Because logarithmic saturation in standard GHG forcing formulas (e.g., AR6) tends to lower increments at higher concentrations, the ULF model is expected to give upper-bound forcing values. Surprisingly, combined ULF estimates for CO₂, CH₄, N₂O, and O₃ are ~39% lower than the IPCC AR6 central estimates for 1750–2019, with the ULF doubling estimate for CO₂ ~11% lower. This paradox highlights the diagnostic value of simple bounding models that indicates discrepancies with AR6 estimates that should be addressed. Using this framework, solar geoengineering (SG) is found to be likely up to ~12.6–13.8 times more efficient than carbon dioxide removal (CDR), with CDR cooling 85–93% less effective. General GHG removal is ~60% less efficient, making SG up to 2.6 times more effective. The analysis reveals a fundamental asymmetry: Earth responds more strongly to changes in incoming shortwave radiation (albedo) than to changes in outgoing longwave radiation affected by GHGs. These findings underscore an overlooked global albedo crisis. Declining planetary albedo, rapid warming, and urban albedo abuse practices such as dark pavements, roofs, and vehicles are intensifying surface heating, yet remain under-regulated despite cost-effective alternatives. Misrepresentations include satellite-based claims downplaying urbanization’s role in warming contributions especially given alternate studies and their measurement challenges resolving UHI vertical structures area albedo corrections and lack of ERF measurement capabilities compared to ground-based studies. SG should therefore be viewed not as a temporary “Band-Aid” but as a premier mitigation tool. A sustained Annual SG strategy is recommended that combines surface brightening, space-based sunshading, and stratospheric aerosol injection (SAI), especially in the polar regions offering urgent, high-leverage mitigation at a time when delays carry the greatest risks.

Source: ResearchGate

[Ken Caldeira]

Isn't this like saying sashimi is 14 times more efficient than sticky rice?

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[Robert Chris]

But sashimi must be at least 14 times more efficient than sticky rice if what concerns you is how much protein you're getting.

So maybe Feinberg is right that SRM delivers a lot more surface temperature change per 1Wm^-2 than CDR does for a like change in forcing.

It's possible that reading the paper might help answer your question.

Regards

Robert Chris

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From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> on behalf of Ken Caldeira <kcal...@gmail.com>
Sent: 06 September 2025 20:52
To: geoengine...@gmail.com <geoengine...@gmail.com>
Cc: Carbon Dioxide Removal <CarbonDiox...@googlegroups.com>
Subject: Re: [CDR] Solar Geoengineering Likely up to 14 Times More Efficient than CDR: Albedo Misrepresentations in Climate Forcing and Governance - Preprint

 

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[jim....@gwmitigation.com]

Negative Cost Energy 1/10 the cost of sea level rise

Extracted from the paper Sustainably Harnessing the Energy of One of the Most Destructive Forces in Nature.

On a strictly $/MWh basis using widely used reference numbers, the levelized cost of OTEC at ~$44/MWh is more expensive than average utility solar (~$38/MWh) and considerably more expensive than average onshore wind (~$26/MWh), but generally competitive with or slightly cheaper than new natural-gas combined-cycle according to EIA and Lazards’ 2030 reference assumptions (~$48.8/MWh).

However, as a firm, dispatchable, low-carbon energy source, OTEC offers greater system value than its levelized cost of electricity alone suggests, as it reduces the need for storage and flexibility required by solar and wind energy sources. In contrast, wind and solar benefit from rapid cost reductions and broader siting opportunities, supporting wider deployment and further cost declines.

On a present-value (PV) discounted basis of a 31 year annual system cost for each energy type, discounted at 5% for carrying cost, TG is ~8% higher than plain PV, ~4% higher than PV+gas, ~39% higher than wind, but 39–48% lower than firmed solar/wind with 4h storage per Figure 2.

Figure 2. Levelized cost of electricity ($ kWh) (31-year horizon, discounted at 5%) for OTEC, PV (plain), PV + 4 hours battery, PV + 20% gas, Wind (plain, Wind + 4 hours battery)

Current clean energy credits and tax incentives primarily support wind, solar, and nuclear energy, while TG, as opposed to OTEC) lacks similar recognition despite its additional cooling benefits. These benefits are not yet valued for their potential to reduce sea level rise or storm-related damages.

Insurers, coastal governments, and climate funds typically respond to storm and flood damages after events occur, rather than proactively mitigating risks through TG deployment. Addressing this gap could lead to more resilient and cost-effective climate solutions.

The lack of a market mechanism to recognize the cooling benefits of TG technologies puts it at a disadvantage compared to established renewable energy options. Resolving this issue could enhance the technology’s economic competitiveness and contribute to broader climate goals.

6.1 Quantified Illustrative Benefits

Based on conservative assumptions, policymakers should note that avoiding sea level rise (SLR) damages by reducing surface heat is a feasible option. A 25% reduction is possible if heat is subducted to an average depth of 500 meters, thus limiting thermal expansion and mitigating the risk of ice melt. The thermal coefficient of expansion of ocean water is half at 1.000 m compared to the tropical surface, and heat moved into the deep is unable to melt ice or intensify TCs. This would avoid storm damage because the cooling of surface waters can potentially lower the intensity of tropical cyclones. Near-term moderation of the global warming trajectory is achievable through targeted cooling intervention, which would avoid a temperature rise.

6.2 Result

 The Oxford Open Climate Change article "Addressing the urgent need for direct climate cooling: Rationale and options, said that only direct climate cooling has the potential to avert continued temperature rise in the near term and moderate at least some projected climate change. It considered 14 proposed direct climate cooling approaches worthy of investigation for potential application on local to global scales for climate cooling, but only one of these, OTEC, and in part Mirrors for Earth’s Energy Rebalancing, can replace fossil fuels.

As Table 1 demonstrates, wind, solar, and nuclear provide no surface cooling benefit, whereas TG has a potentially negative cost.

Tech	Energy Value	Carbon Benefit	Cooling Benefit	Net Cost
Wind	✓	✓	✗	Higher
Solar	✓	✓	✗	Higher
Nuclear	✓	✓	✗	Higher
TG	✓	✓	✓	Lower (possibly negative)

Table 1. Comparison of wind, solar, nuclear, and TG for their energy value, carbon benefits, and cooling benefits, and ranked the technologies based on their net costs.

OTEC is not included in this table because its benefits are heterogeneous, the tropics are cooled at the expense of the high latitudes, and it doesn’t address sea level rise, the real net cost-benefit that TG uniquely provides, because at best, OTEC only moves surface heat into the mixed layer of the ocean, from where it can return within three months.

The question then is, if TG has a possibly negative cost, why is it not assigned a monetary benefit?

Conventional Levelized Cost of Electricity (LCOE) accounting for these technologies captures only the cost of generating electricity per kWh, excluding climate externalities, whether positive or negative. At best, carbon pricing is introduced as an adjustment, but the impacts of thermal forcing are completely omitted.

TG is distinct because it accomplishes two tasks simultaneously: generating dispatchable renewable energy and actively cooling the climate system by pumping heat from the mixed surface layer into the deep ocean.

It creates a negative forcing that offsets surface warming, thereby making them unique among the energy technologies identified in the Oxford article.  

In economics, any intervention that reduces damages from climate change has a monetary value, usually expressed as:

Benefit=Avoided Damages=ΔT×SCCT​

where:

ΔT = reduction in surface warming from TG deployment

SCCT = marginal damages per °C of warming (analogous to Social Cost of Carbon, for CO₂ but temperature-based).

Current energy comparisons do not credit TG for: reduced extreme weather damages (hurricanes, floods, droughts), avoided thermosteric sea level rise, or reduced adaptation costs (agriculture, migration, infrastructure).

Without this benefit, TG appears more “expensive” than solar, wind, or nuclear energy, but once you include a cooling credit, it becomes “too cheap to meter”.

This blind spot exists due to institutional inertia: LCOE is deeply entrenched as the standard comparator, while disciplinary silos and “energy” economists measure $/kWh, and “climate” economists measure the Social Cost of Carbon (SCC), but few integrate these two approaches.

There is uncertainty in quantification: How many °C of cooling per GW TG deployed? How fast does the effect propagate through ocean–atmosphere coupling? And there is a Policy risk: Governments are hesitant to endorse active geoengineering until risks are clearer.

To address this, we need to develop a Thermal SCC (analogous to the Social Cost of Carbon), assigning a monetary value to each unit of surface heat displaced by TG, and incorporate this as a “cooling credit” into LCOE comparisons, similar to how carbon credits are currently added.

Figure 3 estimates the cooling credit value of approximately 25–30¢ per kWh, reflecting a PV of avoided climate-related damages.

Figure 3. Shows SLR, Storm, and Temperature credits based on a 7.6% TG efficiency, where kWh production is linked to surface cooling, and cooling is then monetized through avoided damages. It builds on SCC-style logic, substituting temperature reduction (ΔT) and related impacts (SLR, storm frequency/intensity, heat stress) as the monetized climate services.

The Low / Medium / High exposure scenarios in the graphic represent different regional vulnerabilities to climate impacts. Low-exposure regions have limited coastal infrastructure or lower storm risk, and high-exposure regions are highly vulnerable to SLR and cyclones; hence, they are assigned a higher $/kWh credit.

The line of reasoning is derived from the Michaelis & Baird (2015) GE Ecomagination challenge entry and the Oxford Open Climate Change (2023) article: “Addressing the urgent need for direct climate cooling: Rationale and options”.

The methodology is:

1. Thermodynamic coupling (Prueitt 7.6%)

• Electric efficiency: ηe=0.076
• Heat removed from the surface warm layer per 1 kWh of electricity (deep-water condenser configuration):

= 13.1579 kWhth x 3.6 MJ = 47.34 MJ = 4.737 x 10-14  ZJ

Which is the “unit of cooling service” delivered per kWh.

2. Map unit of cooling to monetized benefit channels

Treat avoided damages as $ per ZJ of surface heat removed for each channel c:

Vc [$/ZJ]

Where Vc​ is the monetary value in $s of avoided climate damages per unit of surface heat removed, for a specific damage channel c.

Channels into chart: SLR (thermosteric sea-level rise damages avoided, Storm (avoided tropical cyclone damages due to reduced ocean heat available to power extremes), Temp (general temperature-linked damages: heat stress, crop losses, etc.)

3. Compute the $ credit per kWh by channel

Creditc  [$/kWh] = Vc [$/ZJ] x Qhot [ZJ/kWh]

and the total cooling credit is the sum of the credits over all channels.

4. Compute $ credit per kWh by channel

Regional vulnerability is reflected in different Vc values (“exposure multipliers”). In the figure, SLR dominates; Storm and Temp are smaller adders that rise with exposure.

5. Numbers used to replicate bars (clearly marked as illustrative defaults)

These Vc values (in $/ZJ) were chosen so the stacked totals reproduce the heights you posted (≈ $0.25, $0.27, $0.31 per kWh)

Numbers used to replicate bars (clearly marked as illustrative defaults)
These Vc values are chosen so the stacked totals reproduce the heights (≈ $0.25, $0.27, $0.31 per kWh):

• Low exposure:
• VSLR=5.06×1012
• VStorm=2.00×1011
• VTemp=6.00×1010
• Medium exposure:

• VSLR=5.40×1012
• VStorm=4.50×1011
• VTemp=1.00×1011
• High exposure:
• VSLR=6.44×1012
• VStorm=1.20×1012
• VTemp=1.20×1011

Multiply each by Qhot=4.737×10−14  ZJ/kWh to get $/kWh by channel; sum to get the total.

Valuing these credits could provide an innovative policy instrument and net value to society of at least 11¢/kWh (low exposure scenario) to +17¢/kWh (high exposure) over and above the 13.9¢/kWh levelized cost of TG energy shown in Figure 2.

This analysis aligns with World Bank data, which suggests that the costs of SLR could reach $27 Trillion Per Year by 2100.  

 

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[Ken Caldeira]

The issue of relative efficacy of shortwave and longwave forcing has been addressed many times before.

Here are the first three papers I could think of that addressed this issue.

https://journals.ametsoc.org/view/journals/clim/36/3/JCLI-D-21-0980.1.xml

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JD029034

https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2015JD023901

There are some differences but it is not a factor of 14.

This issue was addressed in implicitly in our first solar geoengineering paper where we found that to offset the temperature change caused by CO2 forcing, you needed a greater change in solar forcing.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999gl006086