Trees, photosynthesis, and the cost of carbon capture
Carbon capture means collecting carbon dioxide (CO2) from exhaust gases or from the air. What happens next matters: it can be stored as CO2, or its carbon can be used to make something else.
We already have living systems that take CO2 from the air: trees, other plants, algae, and photosynthetic microbes. They use sunlight to build the organic matter that supports food webs.
Start by protecting those systems. Clearing forests, paving productive land, and polluting water damage the living machinery that people and animals depend on.
Two different approaches
Separate and store CO2
Collect CO2 from exhaust or air, then transport and store it. The carbon remains CO2. The questions are energy, money, scale, storage integrity, and who pays.
Convert CO2 into something else
Photosynthesis uses sunlight to turn CO2 and water into organic matter. Trees, other plants, and photosynthetic marine organisms already do this across the planet. Making fuels or other products industrially also needs inputs and a full energy balance.
Burn wood. Grow wood. Follow the energy.
Burning is a reaction with oxygen. In wood, carbon ends up mainly as CO2 and hydrogen as water when combustion is complete. The chemical energy stored in the wood is released.
Cellulose is a major part of wood. The equations below track one repeating unit, C6H10O5. They are a model of the cellulose cycle; wood also contains lignin, other compounds, and moisture.
Burn cellulose: release stored energy
C6H10O5 + 6 O2→6 CO2 + 5 H2O+ energy (E)
Grow cellulose: put energy back in
6 CO2 + 5 H2O+ energy (E)→C6H10O5 + 6 O2
The reverse chemical change requires the same reaction energy that burning releases, when the starting and ending conditions are the same. E means that reaction energy. The tree gets its energy from sunlight. Real growth and equipment involve losses, so total input energy is greater than the chemical energy stored.
Both equations balance: six carbon atoms, ten hydrogen atoms, and seventeen oxygen atoms on each side. For pure cellulose, 162 grams can produce 264 grams of CO2 when burned; the extra mass comes from oxygen in the air.
Photosynthesis is how the energy comes back
Trees first make sugars using sunlight, CO2, and water. They then use those sugars to build cellulose and other tissues. The growing-cellulose equation above combines those steps. The familiar photosynthesis equation is:
6 CO2 + 6 H2O+ sunlight→C6H12O6 + 6 O2
Trees are sunlight-powered carbon capture. Leaves grow, renew themselves, and decompose. Forests also support wildlife, soils, water cycles, and cooling. Solar panels and industrial capture plants need manufactured equipment, materials, maintenance, and end-of-life recycling or disposal.
For forests to add lasting carbon storage, growth must exceed losses from respiration, decay, fire, and clearing. Protect existing forests and restore suitable damaged land; count the carbon that remains stored.
Plants, animals, and a stabilizing feedback
People and other animals use oxygen and release CO2 through respiration. Photosynthesis takes in CO2, stores carbon in organic matter, and releases oxygen. Plants also respire. The balance depends on the whole ecosystem, including soils, microbes, and marine life.
- CO2 increases
- Photosynthesis can increase
- More carbon enters plants
- The rise in atmospheric CO2 is reduced
This is a negative feedback: the response opposes the original increase. More CO2 can stimulate growth while plants have enough water, nutrients, light, and suitable temperatures. Drought, heat, nutrient limits, and habitat destruction can weaken the response.
Change in atmospheric carbon = carbon entering the atmosphere − net carbon taken up by land and oceans.
If inputs exceed net uptake, atmospheric CO2 keeps rising. A stabilizing feedback slows that rise; it does not guarantee equilibrium. Destroying vegetation can both release stored carbon and remove future uptake.
Marine photosynthetic organisms produce roughly half of Earth's oxygen each year. Marine organisms and decomposition consume much of that oxygen too. Ocean protection matters for food webs, oxygen cycling, and carbon storage.
Do not pave away the living systems we depend on. Do not use the oceans as a dump. Habitat loss, contaminated water, disrupted food webs, and oxygen-poor waters can do severe damage. Atmospheric oxygen is held in a large existing reservoir; the urgent risks include ecosystem damage, local oxygen loss, and loss of carbon uptake.
Storing CO2 and rebuilding fuel are different jobs
- Rebuild wood or fuel: change CO2 into energy-rich material. This needs energy to restore the chemical energy released by combustion. Trees use sunlight.
- Capture and store CO2: separate CO2 from other gases, then compress, transport, and store it. Its carbon stays in CO2. This consumes energy, but it does not require reversing the full combustion reaction.
Direct air capture handles very dilute CO2, which makes separation demanding. A claim about its cost or scale must count the power, heat, equipment, transport, storage, and resulting emissions.
CO2 is a continuing flow, not a one-time cleanup
The IEA estimates global energy-related emissions at 38.4 billion tonnes of CO2 in 2025: about 105.2 million tonnes every day. A removal project must specify tonnes per year, its operating life, and how it is funded each year.
Stored CO2 next year = stored CO2 this year + CO2 injected during the year − CO2 leaked during the year.
That storage balance is separate from the atmospheric balance above. Stored tonnes accumulate while new emissions continue. Capturing at a smokestack prevents some new emissions; direct air capture removes some CO2 already in the air.
| Annual flow or capacity | Tonnes per year | Compared with 2025 energy emissions |
|---|---|---|
| Global energy-related emissions, 2025 | 38.4 billion | 100% |
| Reported operating CCS capture capacity, July 2026 | 68 million | 0.18% |
| Illustrative removal programme | 1 billion | 2.6% |
Matching this emissions flow would require about 565 times the reported operating capture capacity. That arithmetic alone does not include the extra energy, pipelines, wells, operating downtime, or storage obligations. Even a billion tonnes a year addresses only 2.6% of this emissions stream.
The practical question is whether the whole chain can deliver enough verified net tonnes every year at an acceptable cost. A pilot working, a funding announcement, or cumulative tonnes captured does not answer that question.
Context diagram: who pays, who benefits?
People paying
Taxpayers, ratepayers, emitters, or buyers of removal credits
or credit purchases→
Capture and storage
- Separate and compress CO2
- Transport and inject it
- Monitor, maintain, and verify
- Pay for long-term responsibility
and returns→
Financial recipients
Project owners, employees, equipment suppliers, transport operators, and storage owners
Benefit: verified, lasting reduction in atmospheric CO2 relative to the alternative. Costs and risks: energy, money, water, land, leakage, and future liabilities.
- For the people paying: ask what benefit they receive and whether a cheaper alternative delivers more.
- For owners and suppliers: contracts, credits, and public funding can provide revenue. Their financial success and the public's climate benefit are separate results to measure.
- For communities, ecosystems, and future generations: include land and water use, transport risks, storage integrity, and responsibility after the original operator closes.
It is an expense. Who pays?
Storing CO2 does not produce energy to sell. Separation, compression, pipelines, injection, monitoring, and repairs all cost money. Revenue must come from somewhere: a buyer paying for a climate service, subsidies or tax credits, or a use for the captured CO2.
In its September 2022 assessment, the U.S. Government Accountability Office described deployment as an added cost to doing business but currently offers few opportunities to generate revenue
. The Congressional Budget Office's December 2023 review likewise found that capture costs exceeded its value in most potential settings.
A profitable subsidized operator is not proof that the public receives good value. Show the cost per net tonne, who pays it, what was actually stored, and the alternatives forgone. Funding creates an incentive to sell a project; payments should depend on verified results.
Published costs need a date and a boundary. CBO's December 2023 review gave an indicative industrial capture range of $15–$120 per tonne, with transport and storage costing extra. Its cited direct-air-capture estimates included $135–$345 per tonne and substantially higher estimates from other analysts. These are dated estimates, not a complete project price or a guarantee of delivered net removal.
GAO's December 2021 review found that DOE spent nearly $472 million on design work for four coal-capture facilities that were never built, almost $300 million beyond the planned amount for those phases. It documented bypassed cost controls. Funders should enforce milestones, stop payments when conditions are not met, and publish measured results.
The arithmetic of scale
| Assumed cost per net tonne | 1 million tonnes/year | 1 billion tonnes/year |
|---|---|---|
| $100 | $100 million/year | $100 billion/year |
| $500 | $500 million/year | $500 billion/year |
| $1,000 | $1 billion/year | $1 trillion/year |
Scaling the annual tonnage scales the bill. It also requires enough energy, transport capacity, suitable storage sites, permits, monitoring, and money to operate year after year.
Pressure, leakage, and responsibility
Industrial systems commonly compress CO2 for transport and injection into suitable underground rock formations. Geological storage needs sealing layers, sound wells, pressure management, and monitoring. Leaks from wells, faults, or equipment are risks that must be evaluated and managed. Storage safety depends on the actual geology, well integrity, and operating practice.
- Who owns the stored CO2 and the long-term responsibility?
- Who measures leakage and verifies the net result?
- Who pays for monitoring, repairs, and damage after the project stops earning revenue?
Protect and restore living ecosystems. Conserve energy and materials. Require measurable results before committing public money to industrial removal.