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[MIS09-01] How much plastic waste emission do we need to reduce to achieve the Osaka Blue Ocean Vision?
Keywords:Marine plastic pollution, Future prediction, microplastics, particle tracking model
Ocean plastic pollution is currently one of the most prominent environmental issues worldwide. Approximately 80% of marine plastic debris flows into the ocean from land via rivers, with the remaining 20% originating from fisheries litter (Morales-Caselles et al., 2021). The emission of plastic debris from land to the ocean is estimated based on various scenarios, considering factors such as each country's level of economic growth and the distance of coastal areas from urban centers. For instance, under the business-as-usual (BAU) scenario, it is projected that approximately 90 million tons of plastic waste will be discharged into rivers, lakes, and oceans annually by 2030 (Borrelle et al., 2020). Furthermore, it has been reported that the weight of plastic emission into the environment in 2040 is expected to decrease by 78% relative to the BAU scenario if interventions are implemented based on current knowledge and technologies (Lau et al., 2020).
Although estimates of plastic emissions into the ocean based on various scenarios have become somewhat feasible, how much reducing plastic emissions contributes to improving marine pollution remains unclear. While global particle tracking models (PTMs) capable of calculating the abundance of macro and microplastics in the ocean have been developed (Isobe & Iwasaki, 2022), hereafter referred to as II22, it is currently challenging to incorporate various scenarios of plastic emissions due to high computational costs. Additionally, considering the lifetimes of macro and microplastics comprehensively in traditional PTMs poses computational challenges. Therefore, this study employs a probability distribution model (PDM) using the results of II22. This model allows for the calculation of future predictions of plastic abundance in the ocean based on various scenarios.
In the PDM, similar to II22, particles are released from 113 river mouths worldwide, and the dynamics of macro and microplastics are calculated for 21 years from 1990 to 2010. While II22 introduced particle numbers corresponding to the actual plastic emission each year, the PDM sets a fixed monthly input of 100 particles, continuously releasing the same number of particles every year. The number of particles reaching each 10º × 10º grid is counted to determine the probability of plastic arrival by dividing the number of input particles. Ultimately, by multiplying the determined probabilities by the actual plastic input according to the scenario, the abundance of plastic in each grid can be determined. Thus, the strength of the PDM lies in its ability to estimate the abundance of macro and microplastics in accordance with changes in plastic input.
This study estimates the required reduction rate of plastic emissions to achieve the Osaka Blue Ocean Vision (OBOV) using the PDM. This vision was announced at the 2019 G20 Osaka Summit with the aim of reducing additional pollution by marine plastic litter to zero by 2050. Figure 1 illustrates the abundance of plastic in the ocean calculated under scenarios of zero increase in emitted plastic or a reduction of 10-50% since 2019 on a global scale. The results depict the ratio of plastic abundance for each year relative to that of 2019, where a value below 1.0 indicates a decrease in plastic. As shown in Figure 1, even with no increase in plastic input, the abundance of plastic in the ocean exceeds that of 2019. This is because plastic waste already accumulated on beaches contributes to the increase in concentration after 2019 and the disappearance of microplastics from surface waters (settling to the seafloor) is likely outweighed by the emission rate. A reduction of approximately 30% compared to 2019 resulted in a ratio below 1.0. When considering plastics by type, the proportion of microplastics on beaches is higher than those in the ocean, and it is estimated that achieving zero additional pollution from marine plastics by 2050 would require a 32% reduction in plastic input.
Although estimates of plastic emissions into the ocean based on various scenarios have become somewhat feasible, how much reducing plastic emissions contributes to improving marine pollution remains unclear. While global particle tracking models (PTMs) capable of calculating the abundance of macro and microplastics in the ocean have been developed (Isobe & Iwasaki, 2022), hereafter referred to as II22, it is currently challenging to incorporate various scenarios of plastic emissions due to high computational costs. Additionally, considering the lifetimes of macro and microplastics comprehensively in traditional PTMs poses computational challenges. Therefore, this study employs a probability distribution model (PDM) using the results of II22. This model allows for the calculation of future predictions of plastic abundance in the ocean based on various scenarios.
In the PDM, similar to II22, particles are released from 113 river mouths worldwide, and the dynamics of macro and microplastics are calculated for 21 years from 1990 to 2010. While II22 introduced particle numbers corresponding to the actual plastic emission each year, the PDM sets a fixed monthly input of 100 particles, continuously releasing the same number of particles every year. The number of particles reaching each 10º × 10º grid is counted to determine the probability of plastic arrival by dividing the number of input particles. Ultimately, by multiplying the determined probabilities by the actual plastic input according to the scenario, the abundance of plastic in each grid can be determined. Thus, the strength of the PDM lies in its ability to estimate the abundance of macro and microplastics in accordance with changes in plastic input.
This study estimates the required reduction rate of plastic emissions to achieve the Osaka Blue Ocean Vision (OBOV) using the PDM. This vision was announced at the 2019 G20 Osaka Summit with the aim of reducing additional pollution by marine plastic litter to zero by 2050. Figure 1 illustrates the abundance of plastic in the ocean calculated under scenarios of zero increase in emitted plastic or a reduction of 10-50% since 2019 on a global scale. The results depict the ratio of plastic abundance for each year relative to that of 2019, where a value below 1.0 indicates a decrease in plastic. As shown in Figure 1, even with no increase in plastic input, the abundance of plastic in the ocean exceeds that of 2019. This is because plastic waste already accumulated on beaches contributes to the increase in concentration after 2019 and the disappearance of microplastics from surface waters (settling to the seafloor) is likely outweighed by the emission rate. A reduction of approximately 30% compared to 2019 resulted in a ratio below 1.0. When considering plastics by type, the proportion of microplastics on beaches is higher than those in the ocean, and it is estimated that achieving zero additional pollution from marine plastics by 2050 would require a 32% reduction in plastic input.