The Incredible Climate Mitigation Potential of Compost

The largest component of solid waste—food waste (according to this EPA pie chart)—may be one of the most effective tools to fight climate change if municipally composted and applied on rangeland as San Francisco has been doing since 2009. However, they don't have much company.

"In 2010, 97% of America's 35 million tons of food waste went into landfills," as noted here last year, Plus, we also pointed out here last year that according to "a new study from the U.N. Food and Agriculture Organization, food waste Is third-largest greenhouse gas source."

"The research showed that if compost from green waste — everything from household food scraps to dairy manure — were applied over just 5 percent of (California)'s grazing lands, the soil could capture a year’s worth of greenhouse gas emissions from California’s farm and forestry industries," writes Carolyn Lochhead of the San Francisco Chronicle.

Experiments on grazing lands in Marin County and the Sierra foothills of Yuba County by UC Berkeley bio-geochemist Whendee Silver showed that a one-time dusting of compost substantially boosted the soil’s carbon storage. 

The application of compost helps "(p)lants pull carbon dioxide from the air through photosynthesis and transfer a portion of the carbon to the soil through their roots." Ohio State University provides a more elaborate description under the "Carbon and Soil Organic Matter" section of their factsheet [PDF].

"Grazing is the single largest land use on the planet, and most grazing lands are degraded, meaning they have lost carbon," writes Lochhead. "That includes California’s coastal and Sierra foothills, where invasive plant species have displaced native perennials that have much deeper roots and store much more carbon."

The University of North Dakota Energy & Environmental Research Center describes the "two major types of CO₂ sequestration: terrestrial and geologic:"

• Geologic sequestration is putting CO₂ into long-term storage in geologic zones deep underground. It is the method of storage that is generally considered for carbon capture and storage (CCS) projects [from anthropogenic carbon sources].
• Terrestrial (or biologic) sequestration means using plants to capture CO₂ from the atmosphere and then storing it as carbon in the stems and roots of the plants as well as in the soil.

"Enter the city of San Francisco, which composts 700 tons of residential and commercial organic waste every day, the largest such operation in the world," writes Lochhead.

“I’ve been in the recycling business for 30-some years here in San Francisco, and this just was much more transformative than the various things we were trying to do to stop putting carbon into the atmosphere,” said Kevin Drew, zero-waste coordinator for San Francisco’s Department of Environment. “To turn around and start taking it out of the atmosphere was a really revolutionary idea, particularly when it was as simple as putting compost on rangeland.”

Composting as a climate mitigation strategy has attracted the attention of "the American Carbon Registry, an organization that certifies (carbon) offsets in California’s cap-and-trade system. On (Oct. 18), it approved one for compost additions to rangeland."