The good, the bad, and the future: Systematic review identifies best use of biomass to meet air quality and climate policies in California

California has large and diverse biomass resources and provides a pertinent example of how biomass use is changing and needs to change, in the face of climate mitigation policies. As in other areas of the world, California needs to optimize its use of biomass and waste to meet environmental and socioeconomic objectives. We used a systematic review to assess biomass use pathways in California and the associated impacts on climate and air quality. Biomass uses included the production of renewable fuels, electricity, biochar, compost, and other marketable products. For those biomass use pathways recently developed, information is available on the effects-usually beneficial-on greenhouse gas (GHG) emissions, and there is some, but less, published information on the effects on criteria pollutants. Our review identifies 34 biomass use pathways with beneficial impacts on either GHG or pollutant emissions, or both-the "good." These included combustion of forest biomass for power and conversion of livestock-associated biomass to biogas by anaerobic digestion. The review identified 13 biomass use pathways with adverse impacts on GHG emissions, criteria pollutant emissions, or both-the "bad." Wildfires are an example of one out of eight pathways which were found to be bad for both climate and air quality, while only two biomass use pathways reduced GHG emissions relative to an identified counterfactual but had adverse air quality impacts. Issues of high interest for the "future" included land management to reduce fire risk, future policies for the dairy industries, and full life-cycle analysis of biomass production and use. Biomass resources are substantial in scale, diverse in nature and geographically dispersed. We used a systematic review to assess the climate and air quality impacts of biomass use in California. New innovative pathways are being developed to substitute fossil fuels, meet climate objectives and contribute to the bioeconomy-"the future." "Good" uses with beneficial effects include combustion for power, production of biodiesel, and conversion of waste to biogas via anaerobic digestion. Biomass pathways with adverse impacts, considered "bad" include wildfire, the open composting of animal manure, and disposal of municipal solid waste without production of landfill gas.image