Potentials of biochar as negative emission technology

Background and Objective

The demands of climate protection policy on agriculture are becoming increasingly ambitious. At the European level, the EU Commission's "fit for 55" package contains proposals for challenging climate targets by 2030. According to the proposals, the agriculture, land use and forestry (AFOLU) sectors are to be greenhouse gas neutral by 2035, and the EU as a whole is to achieve this goal by 2050.

In order to provide incentives for more climate protection in the AFOLU sector, new business models are to be developed under the heading of "carbon farming". Also according to the Federal Climate Protection Act as amended in 2021, an increase in annual additional carbon sequestration in the land use, land use change and forestry (LULUCF) sector is planned. Germany is already to be GHG-neutral by 2045.

The remaining greenhouse gas (GHG) emissions that cannot be fully avoided are then to be offset by negative emissions to achieve the goal of GHG neutrality. Negative emissions include carbon sequestration in the LULUCF sector. Here, carbon farming is mainly understood as increasing carbon stocks in existing forests, afforestation, agroforestry, and humus buildup in agricultural soils. However, these options have limited potential. Carbon stocks in vegetation and soil can only be increased until a new equilibrium is reached; moreover, this process is reversible due to land-use change, for example. In the case of afforestation and agroforestry, additional land is also taken up.

Biochar from pyrolysis of biomass, which does not degrade in the soil even for centuries, could represent a high potential option for long-term storage of biogenic carbon. However, the option is controversial in the scientific and climate policy debate, considered too expensive, too unsafe, and associated with risks such as soil contamination with chemical pollutants. If the option of producing biochar is to be used in the future, a decision must be made at an early stage. Only then can future investments in physico-chemical conversion of biomass ensure that pyrolysis biochar is produced for long-term carbon sequestration and thus "diverted" from the biological carbon cycle. The production of biochar could then become a key technology for achieving climate targets.

The aim of the project is to summarize the state of knowledge on biochar as an option for long-term storage of biogenic carbon and to derive recommendations for climate policy and research.

Approach

1. Analyses of the development of carbon farming approaches in Germany and the EU and of business models for CO2 certificate trading.
2. Scientific literature analysis on the production of biochars and their properties, in particular with regard to the long-term fixation of carbon, raw material prerequisites, production processes, emission avoidance costs and use options including positive and negative effects.
3. Conducting and evaluating an expert survey on the potentials, opportunities and risks of using biochar in agriculture.
4. Analysis on raw material potentials for the production of biochar. Investigation of the productivity of agroforestry systems, evaluation of long-term observation plots with fast-growing tree species and preparation of a scientific publication.
5. Synoptic compilation of the results on biochar including best practice examples in a Thünen publication for the scientific expert public and development of recommendations for further research and climate policy.

Data and Methods

On the basis of a literature review, expert interviews and an analysis of the C-sequestration potentials of agroforestry systems, the state of knowledge on biochar is compiled and a rough estimate of its potential is derived. Based on this, a synoptic representation is prepared to evaluate the potentials, possibilities and limitations of biochar for the long-term storage of biogenic carbon.

Our Research Questions

• What are the potentials as well as advantages and disadvantages of using biochar compared to other negative emission technologies and/or carbon farming measures?
• Do business models for C-sequestration with biochar meet important sustainability criteria for CO₂-certificate trading?
• How high are the local yield potentials of agroforestry in terms of raw material supply for combined carbonization and bioenergetic use?

• In case of a positive assessment: What are the obstacles on the way to the practical implementation of biochar and can these be removed taking into account different interests (agriculture and forestry, climate and environmental protection, politics)?
• Are there best practice examples in Germany and Europe for C sequestration and soil improvement by biochar, including certification models?