Scalable, economical, and stable sequestration of agricultural fixed carbon.

We describe a scalable, economical solution to the carbon dioxide problem. CO 2 is captured from the atmosphere by plants, and the harvested vegetation is then buried in an engineered dry biolandfill. Plant biomass can be preserved for hundreds to thousands of years by burial in a dry environment with sufficiently low thermodynamic " Water Activity, " which is the relative humidity in equilibrium with the biomass. Maintaining a dry environment within the engineered dry biolandfill is assisted by salt that preserves biomass, which has been known since Biblical times. A "Water Activity" <60%, assisted by salt, will not support life, suppressing anaerobic organisms, thus preserving the biomass for thousands of years. Current agricultural costs, and biolandfill costs, indicate US$60/tonne of sequestered CO 2 which corresponds to ~US$0.53 per gallon of gasoline. The technology is scalable owing to the large area of land available for nonfood biomass sources. If biomass production is scaled to the level of a major crop, existing CO 2 can be extracted from the atmosphere, and will simultaneously sequester a significant fraction of world CO 2 emissions.