Pyrolysis and biochar – Too big a rate for climate and environment
The green tripartite's proposal to set aside 10 billion kroner for pyrolysis in order to achieve agriculture's climate goals in 2030 is too big a bet on a technology that can still be asked more questions than there are answers
Pyrolysis is a process where biomass such as straw or manure is converted into biochar under oxygen-free conditions. In the last few years, some politicians and other players have started to talk warmly about this technique as an important tool to reduce the climate impact of agriculture. Most recently, the parties who entered into the 'Agreement on a green Denmark' in June 2024 proposed a pool for storing biochar produced by pyrolysis of DKK 10 billion. DKK
According to the agreement, pyrolysis can contribute significantly to meeting Denmark's climate goals in 2030. Specifically, that pyrolysis can contribute 0,3 million tonnes of CO2 as early as 2030, and funds are also set aside so that pyrolysis can contribute up to 0,6 million tonnes of CO2 in 2030.
But there is a catch to this. We have today no full-scale pyrolysis plant in operation. In addition, the Green Transition Denmark's calculations show that it will be a long time before pyrolysis has a climate effect. For manure that has gone through a biogas plant, it takes between 8 and 40 years, for straw only a few years, while for wood it takes approximately 30 years before pyrolysis has a climate effect.
At the same time, there are also other challenges in betting on pyrolysis and biochar as a climate solution for agriculture.
Risk of environmentally hazardous substances in biochar
One of the challenges with pyrolysis is that we lack knowledge about which environmentally hazardous substances are formed in the pyrolysis process and which can thus end up in the biochar. In addition to environmentally hazardous substances in biochar, there is also a lack of knowledge about the long-term consequences biochar can have for the food we grow in the fields, our drinking water, biodiversity, the soil's micro-life and other possible negative consequences.
Funds have been set aside to investigate environmentally hazardous substances in the pyrolysis process and the biochar, but these results will not be complete until the end of 2025. We also do not know the long-term consequences of applying biochar to groundwater, crops, the soil and the environment. The studies on the long-term consequences of biochar will not be completed until 2033, which means that we will not have knowledge of potential consequences until we expect to have to bring large quantities of biochar onto the fields.
If biochar turns out to have negative consequences for soil and cultivation, it will effectively be irreversible, as it cannot be removed from the fields again. Therefore, it is very important to have the consequences investigated first, so that it does not become an experiment with our fields and our health.
The technology is untested on a large scale
Another challenge is that pyrolysis technology is still at an early stage and is untested on a large scale. In fact, we have not yet seen full-scale pyrolysis plants in operation in Denmark, although several plants are being established. There is therefore a long way to go before the technology may be able to contribute to the CO2 reductions required in 2030.
However, agriculture's climate action cannot wait, and therefore the climate goals should only be linked to structural restructuring and to initiatives that are more realistic, rather than to a technology that may not be able to deliver the necessary CO2 reductions in time.
Biomass is a limited resource
It will require large amounts of biomass if we are to produce the amount of biochar that is set as political targets. But we have a limited amount of biomass available in Denmark and globally, which can be put into the pyrolysis plants with climatic advantages. We must use biomass for many different functions when we move away from using fossil oil for our products. Straw, for example, is in demand for fodder, deep bedding, biogas and other energy, it can be used as a building material, but also has a soil-improving and CO2-storing effect if it is allowed to remain on the field. Wood is in demand for, among other things, construction, packaging, the clothing industry and the energy sector, but neither straw nor wood are unlimited resources. It is therefore important that we use biomass where it provides the greatest benefit - and not blindly pour it into pyrolysis plants.
Denmark's consumption of wood for the energy sector is already large. For this reason alone, it is important to avoid further imports of biomass from abroad. It will be risky to build a large pyrolysis sector that relies on large amounts of biomass that could have fulfilled other and more valuable functions.
There are still too many unsettled questions regarding pyrolysis for us to rely on pyrolysis to meet agricultural climate targets: Which biomass should be used? What consequences can biochar have for the environment? How should it count in our climate accounting etc. This also applies in particular to a future CO2 tax for agriculture, which should not depend on whether pyrolysis can be done.
Read the report 'Pyrolysis and biochar – a climate solution or an environmental challenge?'
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