Future environmental impacts of key metals and consequences for low-carbon technologies

The environmental benefits of low-carbon technologies such as photovoltaic (PV) modules or electric vehicles (EV) have been under debate since their large-scale deployment requires a drastic increase in global metal production. This is of concern since higher metal demand is known to accelerate ore grade decline and can thereby further intensify the environmental footprint of metal supply. To account for this interlinkage known as the "energy-resource nexus", energy and metal supply scenarios need to be assessed in conjunction. We investigate the trends and drivers of future impacts of metal supplies and low-carbon technologies, such as electricity from PV or production of lithium-ion batteries, considering both metal and electricity supply scenarios. We develop metal supply scenarios for copper, nickel, zinc, and lead, for a use in Life Cycle Assessment (LCA) extending previous work. Our models consider future developments such as ore grade decline, energy-efficiency improvements, and secondary production shares. We also include two future electricity supply scenarios from the integrated assessment model of IMAGE using a recently published methodology. Both scenarios are incorporated into the background database of ecoinvent to realize an integrated modelling approach, i.e., future metal supply chains make use of future electricity and vice versa. Thereby, more consistent databases are created representing future systems which can be used as background for prospective LCAs. The scenarios are incorporated with the Brightway2 packages of Presamples and Wurst. We find that impacts of the modelled metal supplies and low-carbon technologies will decrease in the future. Key drivers for impact reductions are the energy transition, increasing secondary production shares, and decreasing hydrometallurgical copper production shares. Among the modelled metals, changes in copper supply revealed the highest influence on reducing impacts of low-carbon technologies caused by metal supply. Considering both metal and electricity scenarios has proven to be essential since they drive impact reductions in different categories, namely human toxicity and climate change, respectively. Thus, an energy transition can only partly compensate for ore grade decline, i.e., only for climate change impacts, but not generally for other impact categories. To complete the picture of future impacts, more integrated and indepth scenarios are needed as well as scenarios for more metals