The carbon footprint of machine tools and metal working machinery in U.S. manufacturing

Recent research suggests that one-third of the global supply of metals is used to produce machinery and industrial equipment (ME). ME production causes 8% of global greenhouse gas emissions. Yet, our understanding of how much different types of ME contribute is limited. While the energy use needed to operate machines usually enters life cycle assessments, the production of the machines is often neglected, mostly because data is lacking. Here we explore the use of detailed economic input-output data for the United States (USEEIO) to produce cradle-to-gate life cycle inventories for machinery for material handling and metalworking, machine tools, dies, fixtures, and industrial molds. The cradle-to-gate GHG emissions of the investigated machinery were 38 million tonnes CO2e (0.5% of US emissions), compared to 330 Mt for all ME. Materials contributed 46-63% to the carbon footprint of the ME in question, the production of electricity and fuels used in production processes other than materials production contributed 13-28%. Important uses of ME as capital products were in the manufacturing of vehicles, refining, and metal industries. Important uses as intermediate inputs were oil and gas production, mining, as well as manufacturing and commercial structures. This manuscript demonstrates the feasibility of using detailed input-output tables for life cycle inventory modelling of the production and use of ME.