Footprints of carbon and nitrogen: Revisiting the paradigm and exploring their nexus for decision making

• Paradigms behind development of footprints should be revisited.
• Proposed enhanced carbon (C) and nitrogen (N) footprints based on paradigm review.
• Decisions change when different paradigms are adopted, hence caution should be used.
• Tradeoff exists in using multiple metrics as shown by C–N footprint nexus.
• Agriculture, Livestock, Forestry and Fishery is the key sector for C–N management.

Paradigms used for developing footprint metrics define the efficacy of these metrics for guiding decisions in the correct direction. Several metrics in use are developed from a narrow viewpoint of only looking at the output side impact of human activities on natural systems. This underestimates or overlooks other impacts on natural systems that occur due to input side interaction of human systems with natural systems. We revisit the paradigms used for development of footprint metrics and analyze the carbon and nitrogen footprints from these perspectives. Based on our analysis, utilizing both input and output side footprint measures is suggested such that heterogeneity of the nature of impact on both sides is not ignored. Utilizing these viewpoints, updated carbon and nitrogen footprints are proposed. Eco-LCA data for 2002 US economy is used to study the effect on decisions if these updated metrics are used. We also highlight the importance of understanding the multidimensional nature of environmental impacts that does not get captured by a single footprint, thus necessitating attention to the nexus of various footprints in decision making. Thus, the nexus between the updated carbon and nitrogen metrics is studied to show the shift in decisions resulting from looking at multidimensional impacts. Results for the US economy show that revisiting the paradigm for development of footprint metrics is a crucial step to avoid pushing decisions in incorrect directions due to use of narrowly focused footprint measures.