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Carbon Footprint Estimation
Scott Matthews,   Carnegie Mellon University
Christopher Weber,   Carnegie Mellon University
Chris Hendrickson,^*   Carnegie Mellon University

Carbon footprints for firms can be regarded as portions of full life cycle assessments. Protocol definitions from carbon registries generally suggest estimating only direct emissions and emissions from purchased energy, with some additional analysis on supply-chain emissions. In contrast, comprehensive environmental life-cycle assessment methods are available to track total emissions across the entire supply-chain, including a wide range of potential environmental impacts. Experience suggests that following narrowly-defined estimation protocols will generally lead to large underestimates of carbon emissions for providing products and services. Direct emissions from an industry are on average only 14% of the total supply-chain carbon emissions (often called Tier 1 emissions), and direct emissions plus industry energy inputs are on average only 26% of the total supply-chain emissions (often called Tier 1 and 2 emissions). Without a full knowledge of their footprints, firms will be unable to pursue the most cost-effective carbon mitigation strategies. We suggest that firms use a broad set of carbon emissions analysis tiers to set the bounds of their footprinting strategy to ensure that they do not ignore large sources of environmental effects across their supply-chains. Such information can help firms pursue carbon and environmental emission mitigation projects within their own plants but also across their supply-chain.

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^* corresponding author: cth@cmu.edu