Biochar: harnessing nature’s carbon capture to fight climate change

The critical role of carbon dioxide removal in mitigating climate change

Let us start by stating the obvious: climate change needs urgent action. More specifically, even if we stopped emitting greenhouse gases today, global temperatures would not decrease for centuries. Furthermore, there are also so-called 'hard-to-abate' emissions, which are emissions that are either excessively expensive or even impossible to avoid with currently available abatement technologies. Examples of such emissions can be found in various sectors, particularly in heavy industry and heavy-duty transport. Therefore, in addition to greenhouse gas (GHG) emissions reductions, active carbon removal from the atmosphere, through so-called carbon dioxide removal (CDR) methods, is necessary for climate change mitigation pathways limiting global warming to 1.5°C. These CDR methods can lower net GHG emissions in the near term, counterbalance 'hard-to-abate' emissions, and enable the achievement of net zero in the long term.

Harnessing ancient solutions for modern challenges: the role of biochar in carbon dioxide removal and soil enhancement

Technologies that capture CO₂ directly from the air (direct air carbon capture and storage, DACCS) exist. Still, these are currently the costliest CDR methods, which hinders their large-scale deployment. However, there are also biological CDR methods that use plants. Plants use a process called photosynthesis to transform light energy into chemical energy, thereby converting water, carbon dioxide (which they take from the air), and minerals into oxygen and energy-rich organic compounds. Photosynthesis has been around for billions of years and is the basis of all life on Earth. Today, the most common CDR methods using photosynthesis are afforestation (planting trees on fallow land), reforestation (restoring forests after deforestation), improved forest management (sustainable use of existing forests), agroforestry (integrating trees with crops and livestock), and soil carbon sequestration (storing atmospheric carbon in soils through increased vegetation).

Biomass contains carbon that was originally captured by plants using photosynthesis. Eventually, this carbon is released back into the atmosphere as CO₂ through micro-organisms, animals, or humans (think of the vegetables we eat). Biochar is another CDR method. It is a charcoal-like material produced through the pyrolysis of biomass. Pyrolysis means the biomass is heated to elevated temperatures without oxygen. The latter fact distinguishes pyrolysis from combustion. During pyrolysis, the biomass undergoes different chemical reactions, which make the carbon that remains in the biochar much more resistant to the decomposition biomass usually undergoes. Therefore, the carbon in biochar can be stored much longer. Even though the exact number is uncertain and varies with the type of biomass and pyrolysis conditions, it is generally accepted that 75% of the carbon in biochar is still stored after 100 years. Since 2018, biochar has been included in the list of CDR methods of the Intergovernmental Panel on Climate Change (IPCC).

Not only photosynthesis is a very old process, so is biochar. Terra preta, or Amazonian dark earth, is a very dark, fertile soil found in the Amazon rainforest. Ancient civilizations living there 2000 years ago made it by adding biochar to the soil. Of course, they were not faced with climate change, so why were they producing biochar? This brings us to the second major benefit of using biochar. When applied to soils, it improves soil properties and increases soil productivity. The improvement of soil properties happens, amongst other things, through better retention of water and nutrients. Therefore, biochar also provides a potential avenue for solving other environmental issues, such as drought and eutrophication.

Biochar can be produced from any type of biomass. Still, residual streams (such as agricultural residues, forestry waste, animal manure, and sewage sludge) are preferred so as not to compete with food production. Biochar fulfills yet another environmental benefit by providing a way to manage residual biomass.

Biochar's emergence in climate strategy

However, despite many benefits associated with its use, biochar remains a relatively unknown and small-scale CDR method. The term biochar was first used at the beginning of this millennium and first related to climate change about five years later. The idea has been around for some time, but the biochar industry has only really grown in the past five years. Hence, biochar could be on its way to becoming more widely known. Nonetheless, difficulties still need to be solved (i.e., with legislation) due to biochar's variability and versatility. Even though we speak of biochar as a single product, it is not. The properties of biochar vary significantly depending on the biomass used and the specifications of the pyrolysis process, particularly the temperature, which can vary from 400°C to 900°C. Biochar can also be used in many different applications. As mentioned before, it can be used as a soil amendment. Still, it can also be used – amongst others – in construction materials, wastewater treatment, feed additive for cattle, or as a substitute for peat in growing media. Of course, the economic and environmental effects depend on the type of biochar and its application.

How trustworthy carbon markets are powering biochar's growth

The development of a trustworthy market for voluntary carbon credits has helped the growth of the biochar industry. Different standards exist, often using third-party verification, and some platforms harness the power of blockchain to increase transparency and integrity in carbon credit trading. In 2022, the voluntary carbon market traded 254 million tons of CO₂ at an average price of $7,37 per ton CO₂. On trustworthy platforms using blockchain, the price can exceed $100 per ton CO₂. The trustworthiness of the market for carbon removal credits is set to increase further as the EU is nearing the completion of its own Carbon Removal Certification Framework.

In conclusion, biochar stands as a promising nature-based CDR technology, despite some hurdles it still faces. Encouragingly, the industry has seen serious growth over the past five years, reflecting its potential and trajectory towards overcoming these challenges.