The research team, led by Chunyan Si and Petar Sabev Varbanov of the Pázmány Péter Catholic University network along with colleagues including Yee Van Fan and Lidija Čuček, focused on the European Union’s twenty-seven member states, where packaging accounts for 39 percent of all plastics conversion. Their model simulates the period from 2018 to 2030, beginning with the year the EU’s single-use plastics restrictions took effect and China’s import ban on plastic waste reshaped global recycling flows. Four materials compete within the simulation: conventional low-density polyethylene, polylactic acid bioplastic derived from corn, kraft paper, and natural cotton, each with distinct weights, lifespans and end-of-life pathways.

What distinguishes this framework from a conventional life cycle assessment is its treatment of time and feedback. The model is built from 144 interconnected system elements organised into five subsystems: demand, production, consumption, end-of-life management and environmental impact. Causal loop diagrams map the reinforcing and balancing feedbacks, such as how growing reuse inventories of durable bags suppress new production, which in turn lowers emissions until those bags wear out and demand surges again. Stock-flow equations then translate these relationships into quantitative projections, with 74 equations and 70 parameters drawn from official statistics, technical reports and published life cycle inventories.

The reuse assumptions are grounded in observed behaviour rather than idealised scenarios. Kraft paper bags, which last roughly a year and a half under favourable conditions, are assumed to survive between one and three uses before moisture and handling destroy them. Cotton bags, with an estimated three-year lifespan, are credited with 50 to 150 uses. Plastic and bioplastic bags remain strictly single-use, reflecting prevailing retail practice. Crucially, the functional unit is a single carrier bag of equivalent 15-litre capacity, so the model compares services rather than objects, and material-specific mass differences, from 18 grams for plastic to a hefty 456 grams for cotton, are explicitly accounted for in every calculation.

Validation against historical data from 2018 to 2021 lends the projections credibility. Mean error rates for population, bag demand, waste generation and landfill accumulation all fell within plus or minus 6 percent, and the model reproduced landfill trends with a coefficient of determination of 0.81. Weaker correlations for bag demand and waste generation reflect the limited year-to-year variation in the short historical record rather than structural flaws, the authors note. With the model thus anchored, the team ran single-material strategies, in which one bag type serves the entire market, and four mixed scenarios in which the plastic share declines in steps of 20 percent, culminating in a consumer-preference scenario with 50 percent cotton informed by European survey data.

The single-material results upend several popular assumptions. Polylactic acid bioplastic emerges as the clear environmental winner on the two metrics studied, cutting greenhouse gas emissions by 42.3 percent and energy consumption by 55.4 percent relative to conventional plastic by 2030, figures consistent with independent life cycle literature. Yet the authors caution that bioplastics accounted for only 0.5 percent of global plastic production in 2022, and a full substitution would raise global agricultural land use by an estimated 1.2 percent, competing with food production. Kraft paper, meanwhile, performs worse than plastic on emissions under every reuse level tested, remaining 2.4 to 20.1 percent higher by 2030, because paper manufacturing emits up to seven times more greenhouse gases per unit than plastic production, though its energy consumption is generally lower thanks to plastic’s fossil-intensive feedstocks.

Cotton tells the most dramatic story of all. Producing one cotton bag consumes roughly the energy of manufacturing 400 conventional plastic bags, so at low reuse rates of 50 uses the cotton pathway ends 2030 with emissions 49.7 percent above the plastic baseline. Push reuse to 150 uses, however, and the picture inverts: emissions fall 18.9 percent below baseline and energy consumption drops by 47.2 percent. The model also captures the characteristic oscillations of reusable systems, in which emissions and energy use rise as new bags are produced, fall once reuse inventories saturate demand, then climb again as bags reach the end of their lifespan and production must resume.

The mixed-material scenarios reveal that phasing out plastic alone is not enough. Under low reuse conditions, every substitution scenario produced higher emissions than the all-plastic baseline, with the cotton-heavy Scenario 4 reaching 37.7 percent above baseline. Under high reuse, the same scenarios delivered emissions reductions of 8.5 to 20.3 percent. Energy consumption, by contrast, fell in every scenario at every reuse level, ranging from 5.6 to 45.1 percent below baseline, because plastic’s petroleum-based raw materials are so energy-intensive. The lesson is stark: reducing plastic production and raising reuse intensity must proceed together, or well-intentioned substitution can backfire on the climate.

Sensitivity analysis sharpened the policy implications further. Shifting 5 percent of waste from landfill to recycling cut simulated emissions by 5.63 percent and energy use by 6.47 percent, whereas an equivalent shift to incineration changed outcomes by less than half a percent. The most aggressive waste-management improvement tested, a 10 percent recycling increase combined with a 15 percent landfill reduction, lowered emissions by 11.10 percent and energy consumption by 13.34 percent. Reuse frequency proved even more powerful: extending cotton bag reuse from 50 to 150 uses reduced emissions by 45.8 percent, dwarfing the effects of any macroeconomic parameter. Even accounting for degraded recycled material quality, which raised emissions by up to 12.97 percent at the lowest substitution factor tested, the relative ranking of scenarios held firm.

The authors acknowledge limitations, including the exclusion of retail distribution, secondary household uses of plastic bags, and impact categories beyond emissions and energy such as land use and water depletion. Still, the framework offers policymakers a transferable tool for testing packaging strategies before committing regulatory resources, and it delivers a clear message for consumers: the environmental value of a reusable bag is not fixed at the factory gate but earned, use by use, in the years that follow. A tote bag abandoned in a cupboard is, by this accounting, one of the most carbon-expensive objects a household can own.

Subject of Research: System dynamics simulation of greenhouse gas emissions and energy consumption across plastic, bioplastic, paper and cotton carrier bag life cycles in the EU-27

Article Title: System dynamics modeling for simulating greenhouse gas footprint and energy consumption of plastic packaging and its alternatives

Article References: Si, C., Fan, Y. V., Čuček, L., Teng, S. Y., Dokl, M., Lendvai, L., Kravanja, Z., & Varbanov, P. S. (2026). System dynamics modeling for simulating greenhouse gas footprint and energy consumption of plastic packaging and its alternatives. Cleaner Engineering and Technology, 34, Article 101305. https://doi.org/10.1016/j.clet.2026.101305

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101305

Keywords: system dynamics, life cycle assessment, plastic packaging, carrier bags, bioplastics, reuse, greenhouse gas emissions, energy consumption, circular economy, EU policy, recycling, cotton tote bags