Composting: A Greenhouse Gas Mitigation Measure

Ton for ton, composting reduces GHG emissions from organics management over any other management option.

compostCompostable organics make up 30% of California's overall waste stream, contributing over 12 million tons annually to our state's landfills. In landfills, this material undergoes anaerobic decomposition and produces significant quantities of methane, up to 80% of which is not captured by a landfill gas system. Composting, on the other hand, is a fundamentally aerobic process, and well managed compost facilities do not produce any methane. Composting offers an environmentally superior alternative to landfilliing organics that eliminates methane production, provides a series of economic and environmental co-benefits, and has a substantial impact on greenhouse gas reduction.

  • Composting organic material reduces GHG emissions compared to landfilling with energy recovery systems. According to the most conservative estimates, which fail to account for many (if not most) GHG-reducing benefits of composting, California could reduce its GHG emissions by one million MTCO2E by composting just 30% of the foodwaste that is currently disposed. This is equivalent to the carbon sequestered by 26 million tree seedlings grown for 10 years.
  • Compost can significantly reduce agricultural energy demand. Plants grown in compost-rich soil require less irrigation because of the increased infiltration and storage capacity of root systems and the reduction of water runoff, evaporation, and water usage by weeds. Research has shown that the application of compost can reduce the need for irrigation by 30-70%. Given that approximately 8% of the electricity generated in the state is used to run California's massive water supply infrastructure, a substantial decrease in water consumption would significantly reduce energy consumption.
  • Composting provides nutrient-rich soils, which multiple studies have shown results in greater carbon storage in crop biomass.
  • The application of compost results in a reduced need for GHG producing petroleum-based chemical fertilizer, pesticides, herbicides, and additives. These chemicals are carbon-intensive in their production and emit large quantities of global warming pollutants during application and as they decompose in the soil. The use of compost can reduce the need for fertilizers for vegetable crops by 33-66%.
  • The application of compost greatly increases the amount of carbon sequestered in soil. Experimental studies have shown that increased carbon sequestration in soil from composting application was 6 to 40 tons of carbon per hectare.

Learn about what CAW is doing to advance composting efforts:

  • AB 1826 (Chesbro) requires businesses that generate organic waste to subscribe to a collection and recycling service for this material. Take Action! Send in a support letter today!
  • Help end a perverse incentive in state law that encourages the use of yard trimmings as landfill cover (ADC) by supporting AB 1594 (Williams). Take Action! Send in a support letter today!

Secured funding for grants and loans for organics recycling facilities in the new state budget.

Sources Cited:

"Waste Reduction Model (WARM)." United States Environmental Protection Agency. <>.

Conversion of 1 MMT CO2 to Familiar Equivalents. California Air Resources Board. <>.

Sharma, Girja, and Angus Campbell. Life Cycle Inventory and Life Cycle Assessment for Windrow Composting Systems. NSW Department of Environment and Conservation and The University of New South Wales. Sydney, Australia, 2003. <>.

Water Supply Related Electricity Demand in California. Demand Response Research Center. California Energy Commission, 2006.<ttp://>.



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