Yokoi, Ryosuke; Watari, Takuma; Motoshita, Masaharu

Metals play an essential role in human life, while metal use is associated with not only metal depletion but also environmental concerns. To discuss strategies towards the sustainable metal use with lower environmental impacts, quantifying future environmental impacts associated with metal production and exploring effective measures for alleviating the environmental impacts are essential. Therefore, we estimate the global greenhouse gas (GHG) emissions associated with future production of six metals (aluminum, copper, iron, lead, nickel, and zinc) based on the five scared socio-economic pathways (SSPs) for 2010-2100. In addition, we explore the influential parameters of metal cycles to reduce the environmental impacts by scenario analysis. We show that trends for GHG emissions associated with metal production are significantly different among SSPs and time perspectives. The scenario with the largest GHG emissions in 2050 is SSP5, followed by SSP2, SSP1, SSP3, and SSP4, while SSP3 exhibits the largest GHG emissions in 2100, followed by SSP2, SSP4, SSP5, and SSP1. Although the SSPs have a great effect for GHG emissions in 2100, cumulative GHG emissions for 2010-2100 are not significantly different among SSPs, which suggest that only transition of socio-economic situations described by SSPs is not enough for GHG emission reduction associated with metal production. By scenario analysis, we show that the lowering the in-use metal stock level is effective to reduce future GHG emission. Nevertheless, our analysis shows changing only in-use metal stock level will be insufficient if we aim for the cut in GHG emissions in line with climate goals, which is required to maintain temperature change below 2°C. In addition to the transition of socio-economic situation toward sustainability, prompt and multiple actions to improve various parameters of metal cycles are essential towards the sustainable metal use with lower environmental pressure.