Friday, January 11, 2008

plastic bags: why so bad?

after reading that australia plans to phase out plastic bags by the end of 2008, and a multitude of other anti-plastic bag initiatives (like here in san francisco), i decided to do some research: why are plastic bags so bad?

the answers didn't completely surprise me. the main problem with plastic bags is likely the negative impacts if they are disposed of incorrectly (essentially a human behavioral failing) -- and that might be surprising to you!

ok, so we want to analyze the life cycle of plastic bags. let's compare plastic bags to paper bags, which is often what people do. here are a few things to consider:

  • energy to create, and environmental impact of creation: plastic wins. plastic bags are a derivative of the oil refining process, whereas paper bags are made of trees, and sometimes from forests that are not sustainably harvested
  • transportation energy: comparing the bags by carrying capacity, it'd take about 7 trucks of paper bags to transport the equivalent of 1 truck of plastic bags: plastic wins
  • disposal: this is the kicker
    • effects on natural environment: plastic bags, if not disposed of properly, can harm wildlife when ingested. paper bags don't have this problem
    • effects on built environment: plastic bags can clog drains and have caused floods in numerous places. you, like me, likely see the plastic bags swirling around everywhere as a blight on our environment
    • garbage dumps: plastic might win here. from what i've read, neither paper bags nor plastic bags do much decomposing in land fills, and since plastic bags are quite compressible, they actually don't take up that much space. BUT, a lot more plastic bags end up at the landfill than paper.. which leads to:
  • recycling: generally people are far more likely to recycle paper bags than plastic bags. the plastic bag disposal programs are typically cumbersome (isn't it annoying to take that plastic bag back to the store!) and hence not utilized by individuals
in fact, on this recycling point i want to show you a figure from a relatively old study that, while the numbers may not be right, does a good job of conveying the importance of recycling in deciding if plastic bags beat paper:

Table 1 - Choice table. Determines bag preference at varying recycling rates. Either was used when the difference between energy efficiencies are inconsequential. (from Institute for Lifecycle Environmental Assessment: Paper vs Plastic Bags)

now, we should also note that governments and stores banning plastic bags aren't in love with paper, but instead are also trying to get out the message that paper vs plastic is a false dichotomy:
- what about reduction: using neither, instead using your own bag
- what about reuse of paper and plastic bags?
- what about alternatives: biodegradable plastics?

my overall conclusion is that we wouldn't be very concerned about plastic bags if people properly dealt with them. that's why i think biodegradable plastic and programs that make it easier to recycle plastic bags are important (like new york is doing). you could just ban them, but then you have to think about what is filling the void. of course, getting people to use their own cloth bag would be fantastic -- but causing that kind of behavior change, namely getting people to have the cloth bag around right when they need it, is likely quite difficult.

here are the resources (they are few, sorry only have so much time!) i examined:

Google Queries:

[what's wrong with plastic bags]
[environmental impact plastic bags]

1 comment:

Grant said...

Why don't grociery stores have a bag rental program? Like you check out, and they give you 10 canvas bags. Thing is, they cost $1 a piece, unless you return them (within 3 months, say). Then they are free. You forget to bring them back, do it next time.