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  • Sarah Jones

Carbon Management

Carbon removal and carbon feedstocks in a net zero future; in conversation with LanzaTech and Climeworks.

ZCC’s Sarah recently attended the Hello Tomorrow Global Summit where she spoke about Carbon Management with Hussein Dhanani (Global Head of Strategic Partnerships & Deputy CCO at Climeworks), Marilene Pavan (Innovation Manager at LanzaTech), and Vincent Durand (Director & Partner of Consulting at Hello Tomorrow). This blog covers some insights inspired by this discussion.


We know that we need 10Gt/yr of carbon removal from the atmosphere (CDR) to reach our climate goals. We also need carbon to make our modern-day chemicals and materials - but how much?

Using an example for the carbon needed to meet 2050 plastic demand, about 6Gt/yr of CO2, captured mechanically (via DAC, for example) or by photosynthetic organisms (microbes or plants).

Even with continued innovation, CDR is (and will be) resource constrained. It shouldn't be used for avoidable emissions. We need structures to prioritise its use for hard to abate emissions and drawing down historical emissions.

When we stop digging up fossil fuels, carbon will become a limited resource. We need to map out net zero carbon sources and build a hierarchy of their uses. Crops need to be used for food; and DAC captured CO2 is extremely energy intensive to convert to chemicals. Leaving photosynthetic microbes and waste carbon as the best options for most chemicals and materials.

Which carbon source for which use cases? CDR: DAC-CO2, low grade/difficult to convert waste Plastic: waste plastic (in order of: mechanical recycling, chemical recycling to monomers, gasifying to syngas) Chemicals: Photosynthetic microbes, high grade biomass waste (e.g. forestry waste, crop residues, paper&pulp waste)

Carbon Cycles

Life on Earth is carbon-based. All biological materials contain carbon, from our DNA to the cells and molecules in our bodies and in plants, animals, and microorganisms.  Biological molecules consist of carbon bonded with hydrogen and oxygen; and often nitrogen, phosphorous and sulphur also.

The carbon on Earth is naturally balanced in the fast and slow carbon cycles.  The fast carbon cycle involves photosynthesis, respiration and decomposing biomass - the movement of carbon through the biosphere. In the fast carbon cycle photosynthetic organisms take CO2 from the atmosphere and convert it into sugars and other complex carbon molecules. CO2 is released back into the atmosphere when plants and plant-eating organisms use the sugar as energy (respiration), when they decompose, or when they burn.  

The slow carbon cycle, on the other hand, is on geological time scales involving carbon stored in the ocean and deep underground.  It involves carbon molecules vented from volcanoes washing into the ocean, biomass sinking to the seafloor, and plant matter being compressed between layers of mud deep underground.  This happens over 100-200 million year timescales and 10-100 Mt of carbon move through the slow cycle every year.

Since we have been extracting and using fossil fuels, we have disrupted the carbon cycles by rapidly releasing carbon from ancient, stored biomass. Net Zero refers to a state in which the greenhouse gases going into the atmosphere are balanced by removal out of the atmosphere and is the state at which global warming stops. We want global heating to stop at 1.5°C above the pre-industrial global average temperature, beyond which it becomes extremely dangerous and extremely expensive (as described in the IPCC’s special report on the impacts of global heating of 1.5°C above pre-industrial levels).

Simplified diagram of fast carbon cycle, U.S. DOE (2008), Source.

Carbon removal

Most of the work to achieve Net Zero by 2050 will be emissions reduction (80% of the 50 Gt reduction required), but to rebalance our carbon cycles, we also need to remove carbon from the atmosphere.  The IPCC and others project that we will need 10Gt per year of carbon removal by 2050, starting now and scaling rapidly by 2050. This number depends on how rapidly or not we can reduce emissions.

According to the IPCC, Carbon Dioxide Removal (CDR) refers to technologies, practices, and approaches that remove and durably store CO2 from the atmosphere. Importantly, CDR does not include point source capture from industrial emitters, only carbon from the atmosphere; and does not include utilisation of CO2 that results in re-release, only durably stored carbon.  CDR is critical to our Net Zero goals and to all scenarios for limiting global heating to 1.5°C or even 2°C.  CDR targets hard to abate emissions areas, capturing already emitted CO2 in the likely overshoot scenarios, and eventually will be used for capturing legacy emissions to move us beyond net zero and into net negative.

CDR has to be scaled rapidly in the next two decades to stay on track to limit heating below 1.5 or even 2°C.  According to the State of CDR Report by Oxford Net Zero, we are currently removing about 2 Gt/yr, mostly through afforestation and reforestation.  And so we have a huge gap to hit 10 Gt/year by 2050.   

Carbon dioxide removal (CDR) required in various scenarios to stay below 1.5 deg. Source: The State of Carbon Dioxide Removal 1st Edition (2023).

At $100/ton of CO2 captured, CDR is a trillion dollar market, and this potential has incentivised an explosion of innovation in CDR. Methods of CDR include DACCS (direct air capture and storage), biochar, BECCS (bioenergy carbon capture and storage), enhanced rock weather and ocean-based ocean alkalinity enhancement, biomass sinking and direct ocean removal and others.  

At a high level, there tend to be trade-offs between price and energy requirements on one hand and durability and measurability on the other. Where many of the biological solutions are low cost, but less durable or measurable, and many of the engineered solutions are high cost, usually high energy; but are measurable and have high durability. So there are opportunities here for low cost, durable CDR; and opportunities for reducing energy requirements of engineered solutions, and improving MRV (measurement, reporting and verification) of biological solutions.

Direct Air Capture

Direct Air Capture (DAC) has arguably had the most attention in recent years when it comes to innovation and early stage investment.  Climeworks was among a handful of first wave DAC companies who have scaled their technologies.  A second wave of DAC companies focuses mostly on improving the energy requirements and capital costs - critical for the feasibility of DAC.  Zero Carbon Capital has invested in RepAir, a second generation DAC company building modular electrolysis systems that achieve leading energy efficiency and costs per ton of CO2 captured, using 70% less energy than current DAC systems. 

RepAir launches DAC field prototype (2023).

The future of CDR

We need to be careful and thoughtful about how CDR gets used. Resource constraints - including land, energy, water, etc. - means that CDR will be limited and can only be used for hard to abate emissions and net negative drawdown if we are to remain within the 10 Gt modelled and reach net zero by 2050. CDR shouldn’t be used for offsetting emissions where decarbonised alternatives are available. A worst case scenario, for example, is using resource intensive DAC to offset the emissions from fossil energy where low emissions energy alternatives are available. 

Setting up governance and structures to prioritise how CDR gets used might be necessary. Otherwise, we would need to extend the amount of CDR required for the 1.5 deg scenarios, which will not only be costly but becomes unrealistic given resource constraints. Emily Grubert and Shachi Talati argue for scaling CDR under public governance, where an unconstrained for-profit CDR industry would lead to ‘luxury’ applications of CDR (where emissions reductions are possible) and be at odds with climate goals.

Carbon products

Life on Earth is carbon-based.  And also, modern life on Earth relies on chemicals and materials that are carbon-based and currently made from fossil fuels. In addition to carbon removal, we need Net Zero approaches to making all our products that require carbon atoms.  So when we think about carbon management we need to think about what we durably store as CDR, and what we use as carbon feedstocks. 

As it turns out, petrochemicals are very handy and very difficult to replace! Read our previous blog: Beyond fossil fuels: carbon-based chemicals without the emissions. Non-fossil sources of carbon include CO2 captured from the atmosphere (CCU), biomass (trees, crops and microorganisms), biomass waste, and existing carbon products (plastics).  Most utilisation of carbon ends in CO2 being re-released and so only DAC and biomass sources are in line with Net Zero, unless the end product is a building material or plastic where the carbon is locked up for a long time (100 years duration is considered permanent for carbon credits). 

Schematic showing some of the alternative feedstocks and emerging technologies we will need to defossilise carbon-based chemicals. Source: Beyond Fossil Fuels, Zero Carbon Capital (2024).

To understand the balance between carbon removal (burying carbon to meet our CDR goals) and carbon feedstocks (using carbon to make chemicals and materials), we need to think about the volumes of carbon-based products required and the volumes of available feedstocks.  

As an example: according to an Oxford Smith School report, to meet the 2050 demand for plastics, 4.5 Gt of CO2 must be captured either mechanically or by growing biomass.  This is on top of the 10 Gt CDR required. And furthermore we need carbon for all our other chemicals and materials, where the total demand for carbon-based petrochemicals is currently around 500 Mt.  This would be roughly 5.6 Gt CO2 (from DAC or biomass) to make our carbon-based chemicals and materials.  Of course, recycling will be essential and could address a significant portion of this, particularly for plastics, but as demand for carbon-based chemicals and materials increases, we need to think carefully about where we get our carbon from. In summary we need about ⅔ carbon for CDR, and ⅓ for carbon products.

Of the available non-fossil carbon sources, microorganisms, biomass waste and plastic waste are particularly promising, although not without challenges to overcome.  We shouldn’t make chemicals from crops because of food security repercussions and land use change emissions.  And converting captured CO2 to chemicals will be a significant burden on energy supply and we should again think carefully about what gets made this way.

Using captured CO2 for making chemicals and materials is hugely energy intensive.  This is because, in addition to the high energy requirements for capturing the CO2, CO2 is a stable molecule that takes a lot of energy to convert into longer carbon chain compounds.  And on top of this, hydrogen is often required for e-fuels and e-chemicals (chemicals made from CO2 and H2), and producing electrolysed hydrogen is even more energy incentive than capturing and converting CO2.  

As an example, methanol demand is currently 150 Mt (and projected to increase to 500 Mt by 2050). The energy required to make e-methanol is ~12 MWh/t (10-11 MWh, most for making green hydrogen and ~1 MWh for DAC).  So, 1800 TWh is required to produce the hydrogen needed to make e-methanol to meet our current methanol demand, which is 7% of current global electricity production (and as high as 14% of 2050 electricity production to meet the 2050 demand).  And this is just for methanol, there are another 350 Mt of petrochemicals to replace.

Similar to the proposal for governance and structures to guide the use of CDR for hard to abate and historical emissions, a hierarchy of uses for the various carbon sources for producing our carbon-based products would help us reach net zero feasibly and efficiently. If we aren’t digging ancient carbon out of the ground anymore (which has extraction emissions as well as production and use emissions), then we need to get better at using waste, microorganisms, and in some cases captured carbon, to make products and maintain our modern quality of life.  It is essential to understand that non-fossil carbon is a limited resource and we should plan for the best uses of the available feedstocks in order to feasibly achieve the transition that is required to stop global heating.  

Industrial Biotechnology

A promising solution for carbon-based products is industrial biotechnology - the use of microorganisms that are able to capture CO2, use methane, or degrade waste and convert these carbon sources into valuable products.  Zero Carbon Capital has invested in Phycobloom who are engineering algae to produce sustainable aviation fuel (SAF) using sunlight and atmospheric CO2, and twig who use bioengineering to improve yields of microbial biomanufacturing (Above: twig labs in London, 2023).  Enzymes are nature’s catalysts and essential for producing products from biomass sources.  Zero Carbon Capital has invested in Epoch Biodesign who design enzymes to convert plastic waste into reusable monomers, and Level Nine who engineer nanozymes (novel biocatalysts) to convert lignin waste into chemicals.  These companies enable the transition away from petrochemicals.  

LanzaTech is ‘recycling carbon with biology’ and is a success story in Climate Tech and pioneer in carbon utilisation.  

“LanzaTech harnesses proprietary microbial processes to recycle waste carbon gases from industrial activity, turning them into ethanol and other valuable chemicals. These gases, originating from sources like steel mills and refineries, are fed to microbes that ferment them in controlled bioreactors, reducing potential carbon emissions. The resulting ethanol can be used as a sustainable alternative to fossil fuels or as a precursor for materials like plastics and synthetic fibers. This innovative technology contributes to a circular economy, diminishing the reliance on fossil resources and lessening industrial carbon footprints. With the potential to expand feedstocks and product ranges, LanzaTech's approach is a key player in the future of low-emissions chemical and material production.” ~ Marilene Pavan, LanzaTech

Carbon Management: Conclusion

It is essential to take a systems level perspective on carbon management.  How much of the carbon we capture should be buried as CDR? And how much should be used to make chemicals and materials?  What sources of carbon feedstocks should we be recycling and converting into products? What innovation is needed to address the challenges with these various carbon feedstocks? 

It will take a massive effort to capture and store CO2 to meet our 10 Gt carbon removal goals. And it will also require deep innovation to find and scale net zero approaches to producing chemicals and materials to replace petrochemicals.  Luckily, there are already inspiring scientific founding teams working on the solutions we need.

If you are a scientific entrepreneur working on a novel CDR approach, or a technology for replacing petrochemicals - please get in touch!


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