Two-thirds of U.S. industries fail to measure 75 percent of their total greenhouse gas emissions by only considering impacts from their operations and energy use, according to Carnegie Mellon University researchers.

They warn that the most commonly used reporting frameworks only cover a fraction of industries' true carbon footprint. Omitting supply chain emissions may leave companies unprepared to pursue the most cost-effective emissions mitigation strategies.

"By far, most companies are pursuing very limited footprints -- toe prints really -- instead of comprehensive ones," said H. Scott Matthews, a Carnegie Mellon associate professor.

Matthews, along with Carnegie Mellon's Chris Hendrickson and Christopher Weber, wrote in an article in Environmental Science & Technology that most protocols only use two tiers of emissions in calculating carbon footprints: emissions from company activities and purchased electricity. Emissions from tier three -- the entire supply chain -- are rarely factored in.

For instance, emissions for the publishing sector from these first two tiers only add up to 6 percent of its total footprint, missing those produced from the manufacture and final delivery of its goods. In the average industry, 14 percent of emissions are generated in tier one activities, with an additional 12 percent coming from tier two.

In its article, "The Importance of Carbon Footprint Estimation Boundaries," the researchers detail a screening-level analysis that can be used to explore supply chain emissions. They've also developed a website to assist the analysis of industry carbon footprints.