Last week, I blogged here about a new NRDC Fact Sheet on biochar, which previewed the publication of NRDC’s biochar scoping study. Today, I’m happy to announce the release of that study, entitled Biochar: Assessing the Promise and Risks to Guide U.S Policy.
For those who want to dig a bit deeper on biochar, the report describes biochar production pathways—different combinations of biomass feedstocks and conversion processes that can be used to produce biochar—and the energy co-products that result and their potential uses. It goes on to assess what is known about the potential benefits of biochar use and the key environmental risks of biochar systems, including a discussion of prospective feedstocks and conversion technologies and their relative strengths and drawbacks in terms of environmental performance. It then takes a critical look at estimates of global potential for biochar production and carbon sequestration, and gives a brief overview of existing domestic and international policies on biochar, before concluding with NRDC’s recommendations for a research and demonstration strategy to help mitigate uncertainties about biochar’s lifecycle environmental impacts and ensure U.S. policy on biochar is developed on the basis of sound science.
The report groups the environmental concerns surrounding biochar into two buckets. The first includes those associated with bioenergy in general—namely concerns about the sustainable supply of biomass for biochar production, including the impacts of biomass production, harvest, transport, and conversion. The second relates specifically to biochar, including the technical uncertainty about the characteristics of various proposed biochar systems, inconclusive or insufficient data on the agronomic performance of biochar in soils and the stability of biochar-based carbon in soils, and the challenge of monitoring and verifying carbon offsets based on biochar application.
A key theme is that the environmental performance of biochar systems depends on the feedstock used, the conversion process employed, and the manner in which the biochar is handled, transported, and applied, and that any assessment of the impacts of individual biochar systems—particularly their net carbon benefits—must take into account the energy required to produce, collect, transport and process the feedstock, as well as the potential for soil carbon loss during the production, harvest and application of the biochar. However, we identify the lack of commercially operating biochar production systems—and, therefore, a shortage of actual chars for field trials—as a major barrier to understanding the performance of different biochars. (More on that in a bit when I discuss our recommendations).
Based on what is known, the report points to already concentrated sources of waste biomass, such as animal manures, organic municipal solid waste and urban wood residues, as preferable to primary biomass, since these do not incur the energetic costs and carbon emissions from land-use change associated with producing primary biomass. It highlights slow pyrolysis as the optimal process for maximizing biochar output and large production systems, uniform feedstocks, and tightly controlled application regimes as likely more reliable from a monitoring and verification standpoint.
As I wrote last week, recent interest in biochar has largely focused on its potential as a climate mitigation tool and enthusiasm has been buoyed by a series of studies offering very large estimates of both our global potential to produce biochar and biochar’s potential to sequester carbon. The report provides a critical discussion of these estimates, arguing that they are largely premature at this time and too uncertain to be considered anything more than upper bound indications of technical potential, while actual achievable potential is likely significantly lower. Instead of focusing just on carbon sequestration, our view is that considering the multiple benefits that flow from well-designed biochar systems—water quality benefits from improved nutrient management, an ability to utilize multiple biomass waste streams as feedstocks, and to produce a variety of renewable energy resources—makes a more robust case for further developing biochar systems.
The report concludes with our recommendations for coupling this more holistic approach with an aggressive, well-coordinated and well-funded research and demonstration strategy. A combination of federal support for the construction and operation of five to 10 biochar production systems and a coordinated five-year national field trial program will ensure that we make available a wide variety of biochars to test on a wide range of soils. This will go a long way towards providing the data we need to systematically classify different biochar systems based on environmental performance and help inform the development of environmentally sound policy on biochar in the U.S.