For a farm that wants better harvests or soil that holds more water, or a company that wants to keep carbon out of the air, residue could offer more than energy. Plants pull carbon from the air as they grow. When their residue rots or burns, that carbon goes back. Part of it could instead leave Jenja as a solid char, and if that char lasts, the carbon in it stays out of the air.
When organic material breaks down or burns, its carbon returns to the atmosphere. Crop residue burned in the field, or waste left to rot, sends its carbon back to the air.
Farming has drained soils too. The world's farmed and degraded soils have lost an estimated 42 to 78 billion tonnes of carbon over time, and adding carbon back to degraded cropland can raise crop yields.49
Carbon from the residue goes one of two ways in Jenja: into the fuel gas, or into the solid that leaves the reactor. Any carbon that stays in that solid does not go back to the air when the gas is burned. If that solid is a carbon-rich char, and if it is stable, it could hold that carbon out of the air for a long time.
The IPCC 2019 Refinement estimates how long char carbon lasts from field and laboratory studies, as the share that remains in soil after 100 years. For char made by high-temperature pyrolysis or gasification above 600 degrees Celsius, it estimates that share at 89 percent.50
Researchers estimated that biochar, char made by pyrolysis and stored in soils, could at most offset about 12 percent of the human-made greenhouse gas emissions of the time, without endangering food security, habitats or soil conservation.51
The next step is to measure what Jenja actually leaves behind: how much char, on which residue, what it contains and how long its carbon lasts. That is when this pathway gets its number.