small-scale farms versus large rangelands that encompass hundreds of thousands of hectares and may be publicly managed) and temporal scales (e.g., short-term versus long-term effects). On top of all this already existing heterogeneity, climate is not only changing, but it is changing differentially across the landscape, and the human population is growing, creating new food demands.

Building a Framework

It was suggested that one way to build a framework for addressing the environmental costs of the food system is to consider the threshold or cut-off rates of application beyond which four key elements—carbon (C), nitrogen (N), phosphorous (P), and sulfur (S)—become pollutants instead of nutrients. The analysis would very site-specific, but at least it would provide a framework for moving forward.

Effects to Consider

Although they did not identify externalities in the pure economic sense of the word, the group participants considered a wide range of effects: soil water erosion, soil wind erosion, soil fertility, water quality, water quantity, water scarcity, biodiversity, air quality/odors, pesticides, herbicides, open spaces, genetically modified organisms (plant and possibly animal), land use change, and deforestation. Additionally, there are several fairly well-known public health effects to consider in relation to some of these environmental effects, for example, asthma and mental health effects associated with exposure to certain odors. Several other considerations not captured in terms of monetization came up during conversation: quality of life; connection to the land; the value of open and green space; animal welfare issues; salt accumulation in soils; the value of wildlife habitat; ecosystem resilience (i.e., some ecosystems are resilient even after abuse, and show no change even when “pushed to the limits,” while others are more fragile and undergo dramatic changes); and weed resistance to herbicides (e.g., some herbicides induce dramatic changes in ecosystem production).

Sources of Information and Challenges in Analyzing the Data

With respect to data, plentiful data are already available in various data networks and databases. Derner mentioned the Long-Term Ecological Research (LTER) Network and the new National Ecological Observatory Network (NEON), both funded by the National Science Foundation (NSF); the Long-Term Agro-Ecosystem Research (LTAR) network and Greenhouse gas Reduction through Agricultural Carbon Enhancement network



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