環境科学：温室効果ガス排出モデルにプラスチックをどのように組み込むのか

Reducing future emissions due to plastics will require a combination of measures, including more biomass use in production of plastics and more recycling, according to a study published in Nature this week.

Plastics are responsible for 4.5% of global greenhouse gas emissions, and contribute to particulate matter emissions and pollution. They are also the bulk material with the fastest growing production: following current growth rates, plastic production and associated CO2 emissions could double by 2050 and treble by 2100.

Paul Stegmann, Vassilis Daioglou and colleagues analyse three alternative CO2 emission mitigation pathways for plastic production through to 2100. They create an integrated model that takes into account plastics’ life cycle from production through waste management. The first pathway, involving partially using biomass to produce plastics and storing waste in landfills, can result in negative carbon emissions in the long term but carries environmental impacts related to landfilling and maintains a high resource consumption. The second pathway, a circular economy approach that emphasizes recycling but excludes an extra push for biomass use in plastic production, achieves 10% greater carbon emission reductions before 2050 compared with the first pathway, yet reduces the potential of negative emissions in the long term. The third pathway, a circular bioeconomy approach combining recycling with higher biomass use in plastic production, achieves the greatest cumulative carbon dioxide emissions reduction while phasing out landfilling and reducing the energy demand of the plastics sector.

The authors propose this circular bioeconomy strategy could turn the plastics sector into a net carbon sink while reducing resource consumption. Achieving this scenario would require improved collection and sorting of plastic waste, a reduction in landfilling, and changes in the design of plastic products.