*4.1. I-O Analysis*

I-O analysis reveals industries that will be a ffected by domestic mineral production. This study considers two extremes; 100% SMS production and 100% recycling. I-O analysis reveals that in a recycling society, 1 unit increase of final demand of recycled copper engenders 1.43 overall units. Table 2 shows the top five industries that will be a ffected.

**Table 2.** Economic ripple e ffect in recycled copper sector.


On the other hand, an increase in deep ocean mining on final demand engenders a 1.75 unit increase, with the top 5 industries shown at Table 3.

**Table 3.** Economic ripple e ffect in domestic copper ore sector.


The estimated ripple e ffect in either case is smaller than for other industries, since the average ripple e ffect of all industries is 2.40. However, observing these impacts, deep ocean mining will relatively increase the output (on a monetary basis) of other industries more than copper recycling alone, as demand for copper increases.

### *4.2. Final Energy Consumption and CO2 Emissions*

Final energy consumption is estimated based on I-O and material flow analysis. In each process, multiple minerals are produced and this study allocates energy consumption and CO2 emissions by the ratio of mass of final products.

Figure 6 indicates domestic energy consumption for the copper recycling scenario. A recycling rate of up to 10% only requires conventional copper smelting due to the relatively low capacity. For rates of 20% and above both conventional and recycled copper processing are required. As the recycling rate increases, the amount of energy required for transportation (collecting end-of-life products) increases rapidly.

**Figure 6.** Final energy consumption in a recycling society.

Figure 7 shows energy consumption required for deep ocean mining. Although the reserves of deep ocean ore are very small relative to the total copper demand in Japan, this limitation is deliberately ignored here. Basically, the deep ocean mining scenario can be considered to be using conventional smelting and refining processes with added domestic mining and ore concentration. Thus, the energy required for mining and concentration processes increases as the supply provided by deep ocean ores increases.

According to this result, domestic mineral production will increase overall energy consumption. In the case of recycling, energy for smelting succeeds in reducing energy consumption due to the utilization of waste plastics and the absence of an oxidization process. However, transportation of end-of-life products consumes the most energy across all processes. In the case of deep ocean mining, mining and concentration processes are added to the current copper production system. The mining processes require more energy than concentration processes. Note that the current import-based system estimate does not consider mining, transportation and concentration processes because these are all currently conducted abroad. As our estimates only encompass the domestic impacts, actual total energy consumption will be greater than our estimate due to international energy consumption.

**Figure 7.** Final energy consumption for deep ocean mining.

Contrarily, CO2 emissions in domestic mineral production may be less than for conventional copper processing. Figure 8 shows CO2 emissions, incorporating those from overseas. It can be seen that deep ocean mining will contribute additional CO2 emissions when compared with current copper production, however, considering the available reserves it is likely not a feasible method to supply Japan's copper ore needs solely from SMS deposits. It is more likely that domestic mineral production will utilize recycling, leading to a reduction in CO2 emissions from copper production. Note that since environmental impact allocation is based on the mass balance, CO2 emissions in mining and concentration of deep ocean mining process are smaller than those in conventional processes. A value-based allocation may change these outcomes.

**Figure 8.** CO2 emissions in copper production.

In addition, Japan's population is forecast to continue to decrease into the future. According to the National Institute of Population and Social Security Research, by 2055, the population in Japan will reduce to roughly 100 million people, approximately 80% of the current population [28].

Table 4 shows the population change observed and forecasted in Japan [28,29]. Following the assumption that copper consumption per person will remain constant, Japan's overall requirements for copper will decrease. Thus, by 2055 we anticipate that environmental impacts will be limited to those shown at an 80% DOM or recycling level in Figures 6 and 7, although alternatively exports could increase to take-up additional copper production. This study assumed that copper consumption per capita and GDP is constant. It has been shown that copper consumption is strongly correlated to GDP per capita [30]. Following the assumption that copper consumption per capita is stable, it is more important to maintain the GDP per capita when considering an aging society, which could lead to a decline in copper consumption commensurate with population decrease.


**Table 4.** Population change in Japan and copper consumption.
