Biochar—plant and animal material turned into charcoal to store carbon—has been proposed as a climate mitigation strategy. But the data so far are inconclusive.
To avoid the worst consequences of climate change, we need to significantly reduce global warming emissions and if possible remove existing carbon dioxide from the atmosphere.
One proposal for achieving the second objective is to heat biomass — plant and animal materials — in a low-oxygen environment to create charcoal, which is mostly just carbon and is called biochar when produced specifically to help reduce global warming.
This report evaluates the potential of biochar as a climate change solution and reviews the scientific literature to assess current data on biochar's long-term stability in the environment.
In theory, biochar might remove carbon dioxide from the atmosphere for extended periods of time, as well as offer other potential environmental benefits
- Through the process of photosynthesis, plants convert carbon dioxide from the air into organic material, or biomass. If that biomass is then used to create biochar and returned to the soil, it has the potential to keep the carbon dioxide from re-entering the atmosphere for an extremely long period of time. It all depends on biochar's stability, or how long it resists decomposition.
- Biochar found in soil can be thousands of years old, so it’s clear that some kinds of biochar resist decomposition, under certain conditions. But there are many different kinds of biochar, and many different soil environments. This report asks whether biochar generally persists for these long time frames.
- In addition to its potential benefits in addressing climate change, incorporating biochar into the soil is also thought to increase fertility, help crop growth, and improve other soil properties.
The idea has attracted considerable attention
- In 2010, the American Power Act — proposed federal legislation to comprehensively address energy and climate change — included “projects for biochar production and use” in a list of project types to be considered for a domestic carbon offsets program.
- The International Biochar Initiative continues to advocate for biochar as a climate change mitigation solution, and it seems likely that more proposals for biochar as a carbon offset will appear at both the domestic and international levels.
Insufficient data exists, however, to assess biochar's stability over long time periods
- Biochar is only effective as a climate change solution if it remains stable in the soil for many years. Otherwise, decomposition will return its stored carbon to the atmosphere.
- This report reviewed the scientific literature on biochar — including 212 references in the peer-reviewed literature that report original research on biochar — and found that the data do not yet exist to accurately estimate biochar stability over time.
- Consequently, it is too early to rely on biochar as an effective climate mitigation tool or to devote public resources to biochar deployment for that purpose.