Comparative LCA: Plastic vs Paper Bags
Using resources • Life cycle assessment and recycling
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Key concepts
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Definition of life cycle assessment (LCA)
A life cycle assessment quantifies environmental impacts of a product across defined stages from raw material to disposal. The assessment uses a consistent functional unit so that different products are comparable. The assessment reports multiple impact categories such as energy consumption, greenhouse gas emissions, water use and waste. A clear system boundary and assumed rates (reuse, recycling, transport) define the scope and influence results.
System boundaries and functional unit
System boundaries specify included stages: raw materials, manufacture, distribution, use, and end-of-life. The functional unit defines what is being compared, for example 'one single-use bag' or 'one bag used 10 times'. Changing the functional unit or extending boundaries (for example including disposal energy recovery) changes comparative outcomes because impacts distribute differently across stages.
Stages for shopping bag LCAs
Raw material stage covers extraction and processing of oil for plastic or wood pulp for paper; higher mass of paper increases resource inputs. Manufacture stage covers conversion into bags, where energy and water use differ by material. Transport stage causes emissions proportional to mass and distance; heavier paper bags cause higher transport emissions per bag. Use stage accounts for reuse: repeated use lowers per-use impacts. End-of-life covers recycling, incineration with energy recovery, composting (paper) or landfill (plastic).
Impact categories relevant to bags
Greenhouse gas emissions (CO2e) measure contribution to climate change. Energy use and water consumption measure resource intensity. Waste generation and litter potential measure pollution and persistence in the environment. Different materials perform differently across categories: one material can score better on greenhouse gases while scoring worse on water use or biodegradability, so multiple categories require consideration.
Comparative manufacturing impacts: plastic vs paper
Plastic shopping bags use less raw material by mass and generally require less energy and water during manufacture than paper bags, so single-use plastic bags often show lower greenhouse gas emissions per bag at the production stage. Paper bag production requires more pulp, energy and water, and produces higher direct emissions during manufacture; higher mass also increases transport emissions per bag.
Use and reuse effects
Reusing any bag lowers its environmental impact per use because fixed production impacts spread across more uses. Lightweight plastic bags that are reused many times reduce per-use impacts substantially. Paper bags tolerate fewer reuses before physical failure compared with stronger reusable plastics; therefore, paper bags usually require more replacements for the same number of uses, increasing their per-use impact.
End-of-life and recycling effects
Recycling reduces the need for virgin materials and lowers overall lifecycle impacts. Paper recycling commonly achieves higher rates than plastic in many regions, which reduces paper's life-cycle impacts when recycling occurs. Plastic recycling rates for lightweight bags are often low; plastic bags that enter landfill persist and contribute to microplastic formation and long-term pollution. Incineration with energy recovery offsets some impacts but creates emissions.
Limiting factors and assumptions
Key limiting factors include assumed number of reuses, local recycling rates, transport distances, production technology, and whether energy recovery occurs at disposal. Small changes in these assumptions can reverse comparative outcomes. A transparent LCA lists assumptions and tests alternatives in sensitivity analysis. Simple comparative LCAs require explicit assumptions for fair comparison and clarity about uncertainty.
Simple comparative conclusion
For single-use scenarios, paper bags commonly show higher energy use, water consumption and greenhouse gas emissions per bag than single-use plastic bags due to higher material and production demands. For multiple-use scenarios, strong reusable plastic bags or increased reuse of lightweight plastic bags often become preferable per use. Paper bags perform better for biodegradability and compostability and often have better recycling infrastructure; the environmental preference depends on prioritized impact categories and realistic reuse and recycling behaviour.
Key notes
Important points to keep in mind