Control of habitat's carbon dioxide level by biomass burning

Pekka Janhunen

REVIEW 2 major objections 4 minor 17 references

Control of habitat's carbon dioxide level by biomass burning

T0 review · 2 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read Burning stored crop waste can regulate CO2 in a space habitat

desk verdict A short conceptual proposal with a correct stoichiometric core and a genuinely new O2-neutral twist, but the control-authority claim needs a dynamic pass before it is fully earned. read the letter →

arxiv 1908.04113 v1 pith:2YWNO22V submitted 2019-08-12 physics.pop-ph

Pekka Janhunen This is my paper · ORCID

classification physics.pop-ph

keywords spacesettlementclosedecosystemcarbondioxidecontrolbiomassburningagriculturalwastecycleoxygenpartialpressureasteroid

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Space settlements with closed ecosystems need to keep atmospheric carbon dioxide between roughly 300 and 2000 parts per million, and their shallow atmospheres hold only a small carbon buffer compared with Earth's. This paper argues that burning stored and dried agricultural waste whenever plant growth pulls CO2 down provides enough control authority to hold that range. The method is robust, low-tech, and scalable, and it keeps the partial pressure of oxygen unchanged because burning and photosynthesis are reverse reactions. If the argument is right, a previously technical obstacle to closed habitats becomes a simple byproduct-management task, and the same approach can bootstrap a growing biosphere by burning sugar or carbon obtained from carbonaceous asteroids.

What carries the argument

The load-bearing mechanism is the stored dry biomass bank: agricultural waste diverted from decomposition, stored so it does not rot by drying, freezing, or freeze-drying, and burned on demand. In the carbon cycle, burning biomass releases CO2 and consumes O2, while subsequent photosynthesis removes the same CO2 and releases the same O2, so the oxygen partial pressure is invariant. The paper's control criterion is a static stored-carbon condition: control authority is sufficient when stored carbon exceeds the maximum carbon fixed in living organisms at any one time, with the burner switched on and off as CO2 crosses its target.

What would settle it

In a sealed chamber with a 50-meter-equivalent atmosphere and actively growing crops, run the biomass burner at its maximum clean-burning rate while photosynthesis is at its peak; if the CO2 concentration falls below 300 ppmv before the burner can respond, the sufficiency claim is falsified. A simpler measurement is to compare the burner's maximum CO2 mass flow per square meter against the 2 kgC/m2/year rainforest fixation rate that the paper cites.

Watch

Extended reading notes

Core claim

The central claim is that biomass burning is a sufficient and practical CO2 controller for a shallow-atmosphere space habitat. Agricultural waste is a necessary byproduct of food production; by drying and storing some of it and burning it at a controlled rate whenever photosynthesis has driven CO2 below target, the settlement restores CO2 without changing O2. The control authority is declared sufficient if the total carbon stored in the settlement exceeds the maximum carbon mass that can be held in living organisms at any one time. Using a tropical-rainforest fixation rate, the paper estimates that burning roughly 0.5 kgC per square meter per year, about 34 kg of dry biomass per hectare per day, maintains authority, with ash output on the order of hundreds of grams per hectare per day and average heating of about 0.8 W/m2.

Load-bearing premise

The paper assumes that having enough stored carbon in the settlement is sufficient for control, without accounting for the rate at which the burner can release CO2 compared with the rate at which peak photosynthesis removes it; in the paper's own example, plant growth could draw CO2 down by 1000 ppmv in 4.5 days.

Editorial extensions

If this is right

A settlement's CO2 can be regulated by routine agricultural management rather than by energy-intensive air-processing equipment such as cryogenic distillation or chemical scrubbing.
The method scales from small habitats to large ones because both waste production and atmospheric volume scale with area; burning frequency, not burner size, changes.
The build-up phase of a biosphere can be supplied with CO2 from burning sugar or elemental carbon sourced from carbonaceous asteroids, avoiding large biomass imports from Earth and avoiding net oxygen buildup.
O2 partial pressure stays essentially constant during both steady-state operation and biosphere build-up, since burning and photosynthesis form a closed oxygen loop.
The paper does not move materials through airlocks, so the method avoids losing atmospheric gases into space.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

We infer that the same storage-and-burn buffer could be adapted to closed non-rotating habitats, submarines, or long-duration spacecraft, with the same oxygen-neutral property, provided a dry carbon stock and fire safety can be maintained.
The static stored-carbon sufficiency condition is not a dynamic guarantee: if a settlement's peak photosynthetic drawdown outpaces the burner's maximum CO2 release rate, the 300 ppmv floor could still be breached. A rate-based control model, absent from the paper, would set the required burner capacity and minimum stored reserve.
If sugar or carbon synthesis from carbonaceous asteroids proves practical, the bootstrap scenario changes the mass balance of early settlement: the limiting resource shifts from Earth-launched biomass to asteroid-derived carbon and water, which is testable by comparing synthesis energetics with launch costs.
Field experiments in sealed greenhouses, burning dried agricultural waste at controlled rates while crops photosynthesize, could measure real smoke and ash loads on windows and plants, a practical concern the paper lists but does not quantify.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Pekka Janhunen's note is a compact conceptual proposal: store agricultural waste and burn it to raise CO2 when photosynthesis draws it down. The core stoichiometry is correct; burning CH2O and reforming it by photosynthesis leaves O2 unchanged, and the 4.5-day timescale for a 1000 ppmv drawdown in a 50 m atmosphere checks out (about 5.5 gC/m2/day). That O2-neutrality is the genuinely new bit, along with the asteroid-carbon bootstrap idea for the growth phase. Nothing in the cited references offers this specific combination, so the novelty claim is fair.

The paper is honest and readable. It does not pretend to be a finished engineering study, and the order-of-magnitude numbers are clearly flagged as such. The references are appropriate; the self-citation to Janhunen's earlier settlement paper [5] is relevant, and the use of Bar-On, Sullivan, and standard ecology sources is sound.

The soft spot is the control-authority claim in Section 3. The sufficiency condition ('total carbon exceeds maximum biospheric carbon') is a static capacity statement, but the actual threat is a rate. If plants can draw down 1000 ppmv in 4.5 days, the burner must be able to inject CO2 at least that fast when the controller calls for it, and there must be enough stored carbon to sustain the injection until photosynthesis slows. The paper gives neither a burner-rate bound nor a feedback law. Also, the upper-bound side is missing: you need T < M + A_upper, not just T > M. If total carbon exceeds what the biosphere can hold plus the atmosphere's upper-limit capacity, CO2 cannot return below 2000 ppmv even with full plant uptake. These are fixable in revision, but they are real omissions.

The rate issue is not fatal. In practice one could size the burner and the stored-biomass bank to handle the worst-case drawdown, and the paper actually contains enough numbers to make that argument. But the central assertion—that the problem 'can be solved by biomass burning'—is stronger than what is demonstrated. A dynamic or quasi-static control calculation would close the gap.

I would send this to a referee. It is a clear, short idea pitched at the right level for a journal note, and the gaps are well-defined enough that a referee can ask the author to fill them. No red flags for fabrication or circular reasoning; the argument is a straightforward bookkeeping exercise, and the main weakness is an overstatement of what the static condition proves.

Referee Report

2 major / 4 minor

Summary. The paper proposes controlling the CO2 level in a free-space settlement with a shallow (about 50 m) N2/O2 atmosphere by storing dried agricultural waste and burning it when plant growth has drawn down atmospheric CO2. The method relies on the stoichiometric pairing of photosynthesis (Eq. 1) and combustion (Eq. 2), which leaves the O2 partial pressure unchanged over the full cycle. The paper gives order-of-magnitude numbers: Earth's atmospheric and biospheric carbon stocks (1.66 and 1.08 kgC/m2, respectively), a maximum fixation rate of 2 kgC/m2/yr, and a 4.5-day timescale for a 1000 ppmv CO2 depletion in a 50 m atmosphere. It further discusses practical engineering issues (smoke, ash, fire risk, storage methods, backup techniques) and the possibility of bootstrapping the biosphere by burning carbon or sugar derived from carbonaceous asteroids. The central claim is that biomass burning robustly, low-techly, and scalably solves the CO2 control problem.

Significance. The core stoichiometric insight is correct, and the paper's order-of-magnitude carbon budget is internally consistent; the O2-constancy argument is a clean and useful observation for closed-ecosystem habitat design. The paper is candid about limitations such as dark seasons, smoke, and fire risk. If the control-authority question were properly settled, the proposal would be a genuinely practical, low-tech solution to a recognized problem in space-settlement engineering. However, the paper's stated sufficiency condition is a static capacity inequality rather than a rate or closed-loop condition, so the central claim that the problem 'can be solved' is not fully demonstrated by the present analysis.

major comments (2)

[Section 3, paragraph beginning 'It is sufficient for only part of the biomass...'] The stated sufficiency condition is a static capacity inequality: total carbon in the settlement must exceed the maximum biospheric carbon stock. It says nothing about the rate at which CO2 can be released. The paper's own Introduction identifies the threat as a rate: maximal plant growth of 2 kgC/m2/yr can reduce CO2 by 1000 ppmv in 4.5 days in a 50 m atmosphere. To keep CO2 from falling below the 300 ppmv lower bound, the burning system must be able to inject CO2 at a rate at least matching the net photosynthetic drawdown whenever the controller calls for it, and the stored-biomass bank must be large enough to sustain that rate for the required period. Neither the maximum burning rate nor a dynamic model of the CO2 balance (e.g., dC_atm/dt = -photosynthesis + burning + respiration) is given. Therefore the abstract's claim that the problem 'can be solved' is not established; a quantitative rate check or a simple feedback analysis is needed.
[Section 3, same paragraph] The sufficiency condition also leaves the upper bound unaddressed. If the total carbon inventory T is too large relative to the maximum biospheric stock M and the carbon equivalent of the upper CO2 limit A_upper, then the atmosphere cannot return below 2000 ppmv even with full plant uptake unless the excess carbon is permanently stored in a non-decomposing form. The paper should state the complementary condition on T (or, equivalently, on the required size and stability of the stored-biomass bank) and discuss what happens if storage integrity fails. Without this, the paper's assertion that 'if there is too much CO2, one ceases the burning activity for a while' is not sufficient as a control law.

minor comments (4)

[Section 3] The term 'control authority' is used several times but never defined; a formal definition (e.g., the maximum cumulative CO2 that can be added, or the maximum sustainable injection rate) would improve precision.
[Section 3, paragraph on burning activity] The claim that 'in a 50 m high atmosphere, enough constant CO2 is reached by a daily burning session' is unsupported by any calculation; a brief quantitative example would clarify the intended operating point.
[References] Reference [6] is a Wikipedia article; a primary source for photosynthesis rates would be more appropriate for a journal publication.
[Throughout] There are minor typesetting inconsistencies (e.g., 'O2' and 'CO2' without subscripts in some places) and the abstract phrase 'the atmospheric carbon buffer per biosphere area is smaller than on Earth' is slightly awkward; consider rewording to 'smaller than Earth's atmospheric carbon buffer per unit biosphere area.'

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity found: O2 conservation follows from stoichiometry and the CO2-control argument is a bookkeeping/engineering estimate with external data; the rate limitation is a robustness concern, not a circular reduction.

full rationale

I walked the paper's derivation chain. The central claim is that burning stored, dried agricultural waste can replenish atmospheric CO2 in a shallow-atmosphere settlement while leaving O2 partial pressure unchanged. The O2-constancy claim follows directly from the balanced reaction pair (CO2 + H2O + light -> CH2O + O2 and CH2O + O2 -> CO2 + H2O + energy), not from an assumed conclusion. The CO2-control argument uses externally sourced carbon-stock and fixation-rate figures (Bar-On et al. [1], Sullivan et al. [2], Wikipedia/Ricklefs [6,7]) to size the biomass bank and burning rate; the 0.5 kgC/m2/year burned scenario is explicitly an illustrative conservative estimate, not a fitted parameter renamed as a prediction. The asserted sufficiency condition ('the control authority is sufficient if the total amount of carbon in the settlement exceeds the maximum mass of carbon that can be fixed in living organisms at any one time') is a static bookkeeping condition; it may be under-specified with respect to rates, since the paper's own 4.5-day drawdown example raises a dynamic-control concern, but it is not circular: the condition is not defined in terms of the conclusion, nor is the conclusion forced by the condition alone. The only self-citation (Janhunen 2018, for sectoring/illumination) appears in a side discussion about seasons and is not load-bearing for the biomass-burning method. No equation, parameter, or normalization is defined in terms of the target result, and no prediction is obtained by inverting an input. Accordingly, I find no exhibited circular step; the identified rate issue is a correctness/robustness concern rather than a circularity.

Assumptions & free parameters 2 free parameters · 5 assumptions · 0 invented entities

The paper's argument rests on standard stoichiometry, a 50 m N2/O2 atmosphere from prior design work, and the assumption that terrestrial semi-closed ecosystems demonstrate closed ecosystem feasibility. It uses rough literature values for carbon fixation and ash fractions, and chooses a 50% burned fraction by hand for a conservative rate estimate.

free parameters (2)

Burned fraction of agricultural waste = 50% (0.5)
Chosen by hand in Section 3 as a conservative estimate; the paper notes it is likely overkill.
Average carbon fixation rate = 1 kgC/m2/year
Assumed average between tropical forest (2.0) and cultivated area (0.65) values from Sections 1 and 3, used to compute the burning rate.

assumptions (5)

standard math Photosynthesis and metabolism are exact reverse reactions with biomass formula n(CH2O) (Eqs. 1-2).
Used in Sections 1 and 3 to argue that burning biomass reverses photosynthesis and keeps O2 constant.
domain assumption A space settlement uses a shallow N2/O2 atmosphere of about 50 m depth.
This is taken from Janhunen [5] and used throughout the quantitative estimates.
domain assumption Closed ecosystems are feasible based on terrestrial semi-closed examples such as gardens and Biosphere-2.
Section 5 generalizes from these examples to full closure; this is an analogy, not a proof.
domain assumption Plants and soil remove atmospheric impurities (Wolverton et al. [10]).
Used in Sections 2 and 5 to argue that smoke and VOCs will be cleaned up naturally.
domain assumption No net oxygen transfer between atmosphere and biosphere in metabolism.
Section 2 states oxygen atoms in CO2 originate from water, so O2 partial pressure stays constant.

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Cite this review

Pith. "Pith review of Control of habitat's carbon dioxide level by biomass burning." pith.science (2026). https://pith.science/paper/2YWNO22V

@misc{pith2026190804113,
  author       = {Pith},
  title        = {Pith review of: Control of habitat's carbon dioxide level by biomass burning},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/2YWNO22V}},
  note         = {Machine review of arXiv:1908.04113}
}

read the original abstract

Consider a free-space settlement with a closed ecosystem. Controlling the habitat's carbon dioxide level is a nontrivial problem because the atmospheric carbon buffer per biosphere area is smaller than on Earth. Here we show that the problem can be solved by burning agricultural waste. Waste biomass is stored and dried, and burned whenever plant growth has lowered the atmospheric carbon dioxide level so that replenishment is needed. The method is robust, low-tech and scalable. The method also leaves the partial pressure of oxygen unchanged. In the initial growth phase of the biosphere, one can obtain the carbon dioxide by burning sugar or carbon, which can be sourced from carbonaceous asteroid materials. This makes it possible to bootstrap the biosphere without massive biomass imports from Earth.

Figures

Figures reproduced from arXiv: 1908.04113 by the authors.

**Figure 1.** Carbon cycle on Earth. Earth’s surface area is open ocean, desert or glacier so that the globally averaged biomass areal density is only moderate. For example in average African tropical rainforest, the carbon stock is 18.3 kgC/m2 i.e. 183 Mg/ha [2, [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗

**Figure 2.** Carbon cycle in the settlement. In a rainforest, the maximum carbon fixation rate is 2 kgC/m2 /year and in a cultivated area it is 0.65 kgC/m2 /year (see last paragraph of Introduction). If the average is ∼ 1 kgC/m2 /year and if 50 % of it is burned while the remaining part is decomposed naturally or eaten as crop, then the burned amount is 0.5 kgC/m2 /year, which corresponds to 34 kg of dry biomass per hectare per… view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

17 extracted references · 17 canonical work pages

[5]

Janhunen, P., Natural illumination solution for rotating space settlements, NSS Space Settlement J. (2018). https: //space.nss.org/media/NSS-JOURNAL-Natural- Illumination-for-Rotating-Space-Settlements.pdf

work page 2018
[1]

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Sullivan, M.J.P., J. Talbot, S.L. Lewis et al., Diversity and carbon storage across the tropical forest biome, Scien- tiﬁc Reports 7 (2017) 39102. https://www.nature.com/ articles/srep39102

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Wang, Y .P., R.M. Law and B. Pak, A global model of carbon, ni- trogen and phosphorus cycles for the terrestrial biosphere, Bio- geosci. 7 (2010) 2261–2282

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Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

[1] [5]

Janhunen, P., Natural illumination solution for rotating space settlements, NSS Space Settlement J. (2018). https: //space.nss.org/media/NSS-JOURNAL-Natural- Illumination-for-Rotating-Space-Settlements.pdf

work page 2018

[2] [1]

Phillips and R

Bar-On, Y .M., R. Phillips and R. Milo, The biomass dis- tribution on Earth, Proc. Nat. Acad. Sci. 115 (25) (2018) 6506–6511. https://www.pnas.org/content/pnas/115/ 25/6506.full.pdf

work page 2018

[3] [2]

Talbot, S.L

Sullivan, M.J.P., J. Talbot, S.L. Lewis et al., Diversity and carbon storage across the tropical forest biome, Scien- tiﬁc Reports 7 (2017) 39102. https://www.nature.com/ articles/srep39102

work page 2017

[4] [3]

O’Neill, G.K., The colonization of space, Physics Today 27 (9) (1974) 32–40

work page 1974

[5] [4]

O’Neill, G.K., The high frontier, New York (1977) 288

work page 1977

[6] [6]

wikipedia.org/wiki/Biomass_(ecology)

Wikipedia article on biomass (ecology), https://en. wikipedia.org/wiki/Biomass_(ecology)

work page

[7] [7]

Ricklefs, R.E. and G.L. Miller, Ecology (4th ed.), Macmillan (2000), 192

work page 2000

[8] [8]

Law and B

Wang, Y .P., R.M. Law and B. Pak, A global model of carbon, ni- trogen and phosphorus cycles for the terrestrial biosphere, Bio- geosci. 7 (2010) 2261–2282

work page 2010