Carbon Removal 101

Updated: Jul 29

By Dr. Andrew Jones, PhD Why do we need carbon removal?

The warming effects of Carbon Dioxide (CO2) from burning fossil fuels were first discovered by Swedish scientist Svante Arrhenius, in 1896. Nearly a century later, American climate scientist James E. Hansen testified to Congress that “The greenhouse effect has been detected and is changing our climate". Figure 1 shows the increase in CO2 emissions due to human activity and the concomitant rise in atmospheric CO2 concentration.

Figure 1: Atmospheric CO2 concentration and annual emissions (Source: NOAA)

In the 1950s scientists first began to worry about climate change. The Clean Air Act was passed in 1970, and it wasn’t until the 1980s that people began to take action against climate change. The first carbon offset project happened in 1989 when the American electric power production firm AES Corp invested $2 million to plant 50 million trees in Guatemala attempting to offset a new powerplant the group had built in Connecticut.

By the late 1980’s we had started experimenting with Carbon Dioxide Removal (CDR) on a small scale. However, after the Paris Climate Agreement was signed in April 2016, CDR took center stage. For the first time, there was a global consensus based on scientific facts that global temperature rise needs to stay below 1.5°C in order to avoid adverse effects of climate change. Most notably, this translates into reducing CO2 concentration in the atmosphere to below 350 ppm (the exact concentration is yet to be determined but it will be somewhere between 300 and 350 ppm). As of May 2022, atmospheric CO2 concentration is at 420.99 ppm. One of the outcomes of the Paris Climate Agreement was the development of a decarbonization pathway for achieving the desired atmospheric CO2 levels that can limit the global temperature rise from 1.5-2°C. Figure 2 shows a decarbonization pathway published by the National Academy of Sciences. Note that this pathway starts with reduction first before tapping into CDR.

Figure 2: Scenario of the role of negative emissions technologies in reaching net zero emissions (Source: National Academies of Sciences, 2019)

Although reductions and avoided emissions should always come first, at this point they are simply not enough to reduce atmospheric CO2 concentration and the consensus is that we need to start removing CO2 from the atmosphere. It is estimated that the planet needs to have 10 gigatons of carbon dioxide removal capacity by 2050, and 20 gigatons of carbon dioxide removal capacity by 2100.

What is Carbon Dioxide Removal (CDR)? To better understand how CDR works, we first need to understand the existing planetary carbon pools. Carbon pools are places where carbon can be found on our planet and the five major pools are defined as:

  1. Lithosphere (66 to 100 million gigatons of carbon). The largest carbon pool that is made up of fossil fuels and sedimentary rock deposits.

  2. Oceans (38,000 to 40,000 gigatons of carbon). Ocean waters contain dissolved carbon dioxide, and calcium carbonate shells in marine organisms.

  3. Soil Organic Matter (1,500 to 1,600 gigatons of carbon). Solid carbon stored in the soil.

  4. Atmosphere. This consists primarily of carbon dioxide, carbon monoxide, and methane.

  5. Biosphere (540 to 610 gigatons of carbon). This consists of all living and dead organisms not yet converted into soil organic matter.

There are carbon fluxes naturally moving between these five pools. Human intervention has interfered with those natural fluxes and has resulted in more carbon entering the atmosphere and changing its balance. Figure 3 shows a schematic of all the existing carbon pools and carbon fluxes moving between those pools.

Figure 3: Schematic of the global carbon cycle (Source: IPCC, 2013)

Carbon removal works by reversing that cycle, taking carbon from the atmospheric pool and storing it in other pools, either naturally or through engineered solutions. Different approaches to carbon removal come with different risks and co-benefits. There are many different types of CDR technologies, the main categories are shown in Figure 4a and 4b.

(a). Carba is a new hybrid solution using natures biomass converted into Graphitic Carbon and permanently buried for thousands of years. (Not shown)

(b). Carba has added graphitic carbon stored underground to this image for illustrative purposed to show where Carba fits in the carbon removal ecosystem. (Shown in bottom right corner)

Figure 4: (a) A diagram summarizing all known carbon removal technologies (b) An artist rendition of carbon removal technologies (Source: National Academies of Sciences, 2019).

A Portfolio Approach

Carbon removal technologies come in a variety of shapes and forms. The important metric that distinguishes carbon removal technologies are quality (permanence and additionality), cost ($/ton of carbon removed), and scalability (Gtons/year). And the main barriers are Measurement, Reporting, and Verification (MRV) of the CO2 removed. However, there is no silver bullet in cracking the carbon removal code, and we need to deploy a portfolio of solutions to achieve the carbon removal goal of 20 Gtons/year by the year 2100. Table 1 summarizes all existing CDR technologies along with their key important metrics.

Table 1: A summary of select CDR technologies and their three key metrics of permanence, cost, and scalability.

Although engineered solutions have attracted a lot of attention especially from Silicon Valley and the Oil and Gas industry, we should not neglect nature based solutions or hybrid approaches. Many engineered solutions come at a high cost and are energy intensive. Although nature-based solutions face challenges when it comes to permanence and MRV, they come at a much lower cost and provide many other ecosystem benefits beyond just atmospheric carbon removal. Increased soil water holding capacity, biodiversity, healthier soils, and higher yields are just a few ecosystem benefits that nature based solutions can provide. Yet, not all nature-based solutions are created equal. A 2016 EU report showed that 85% of the forest projects had no environmental benefit, and there is still scientific uncertainty surrounding the competing warming effects of tree’s albedo and hydrocarbon emissions. If done incorrectly, planting trees can actually harm biodiversity.

One emerging hybrid solution that can have multiple ecosystem benefits is the conversion of biomass into a solid and inert graphitic carbon, which is then stored underground. Carba is an early-stage startup working on this innovative technology. Carba's hybrid technology combines nature-based CDR (plants capture CO2 from the air and convert it to cellulose, hemicellulose and lignin) with engineered CDR (engineered reactors convert plant matter to stable carbon). Natural biomass or agricultural waste that would have otherwise left to decompose and release stored carbon, is instead converted, and buried underground where it is stable for millions of years. Unlike other engineered solutions, Carba’s technology is energy neutral, requiring near zero additional power leveraging the 40+ years of experience of its founders in pyrolysis technology. By converting plant matter to graphite, oxygen is removed from the plant molecules and the resulting solids are infinitely stable in the absence of oxygen underground. As with existing direct-air-capture engineered solutions, Carba’s technology removes CO2 from the atmosphere and stores it permanently. In contrast with other technologies, Carba leverages nature for capturing CO2 avoiding energy intensive separations and compressors, and expensive chemicals, minerals and membranes.

The global carbon economy is still in its infancy and a lot of its mechanisms are still under development at the time of writing this article. Due to market demand and ambitious corporate climate goals, a variety of CDR technologies have emerged much faster than the carbon markets and MRV technologies that are needed in order to govern them. Although all CDR technologies are fighting for the same pie, in reality not a single CDR technology will be able to satisfy the carbon removal demand in the near future, instead we need a plethora of technologies to contribute. The Carbon Removal market is moving fast because we are running out of time. For corporate buyers, a strong emphasis should be placed on the quality of carbon removal offsets in terms of its permanence, energy utilization, and additionality. -- SOURCES: Contributing author: Arian Aghajanzadeh, Klimate Consulting LLC Figure 1: Atmospheric CO2 concentration and annual emissions (Source: NOAA) Figure 2: Scenario of the role of negative emissions technologies in reaching net zero emissions (Source: National Academies of Sciences, 2019) Figure 3: Schematic of the global carbon cycle (Source: IPCC, 2013) Figure 4: (a) A diagram summarizing all known carbon removal technologies, (b) An artist rendition of carbon removal technologies (Source: National Academies of Sciences, 2019

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