[Alas, this is super-intern Justin Brant’s swan song—his last Daily Score post before he moves on to bigger and better things…]
Reader Jonathan Shakes came up with a great idea in response to Clark’s blog post on the absurdity of the paper-vs-plastic debate. Says Shakes: “I’d love to see an illustration from one of the data geeks just why the bag contents matter more than the bag itself.”
Well Jonathan, this data geek accepts your challenge.
Assuming that a grocery bag holds one day’s worth of food for a family of four, the choice about what to put in the bag is about 186 times as important as the bag itself. (For an illustration, see the graph to the left.)
This number was calculated using the concept of embodied energy—the energy used to produce, transport, and dispose of a product over its entire lifetime. For food this includes making fertilizers, processing, transportation, storage, and cooking.
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Here’s my thinking. Using data from the most on-point study I could find, I calculated the energy used to produce, process, transport, store, and cook four servings of two different diets: the first, a meat-based diet that included beef, potatoes, tropical fruit, and drinks such as soda; the second a vegetable-based diet composed of produce grown within the country where is was consumed and a soy-based protein source.
The first diet takes 113 MJ (megajoules) of energy to get to the table, while the second takes 24 MJ of energy. The difference between these two numbers is 89 MJ.
In contrast, it takes about 0.5 MJ (pdf link), give or take, to produce and dispose of one plastic bag.
Thus, the energy saved by four people choosing the vegetable-based diet for one day equals the energy needed to produce 186 plastic bags, or drive the average U.S passenger car over 15 miles.
If anything I’d say the above number is conservative. I didn’t include processed snack food in the high-energy diet, even though highly processed foods can require lots of energy. I also didn’t distinguish between conventional and organic produce, which typically uses less energy to grow than conventional produce.
And by the way—in researching this post, I also came across some good data on the plastic-vs-paper-vs-canvas bag debate. From an energy standpoint, using a canvas bag is 14 times better than plastic without factoring in the littering, landfill, recycling, and foreign oil dependence issues with plastic bags. Canvas bags are also 39 times better than paper, at least from an energy standpoint. Again, this number is conservative, since it assumes that a canvas bag is used 500 times over its lifetime. Some of my canvas bags have been around over 6 years and show no signs of slowing down anytime soon.
Geekage notes: The study used to calculate embodied energy in food is from Sweden and can be found here (pdf link). Bag embodied energy is from an Australian study available here, though other figures are available as well. I’m assuming that the embodied energy for food and bag production in the United States is similar.
Holy cow. This is probably the most useful post on this topic ever! Thank you so much for breaking it down and for the excellent resource.Good luck in your bigger and better things.
There is a problem with the article, although the approach taken is excellent as far as it goes. The problem is that there are other dimensions than just energy. Two of these (related) items are 1) the amount of pollution produced during the life cycle of the bag… pollution in various forms is threatening species survival, the food chain, our health (due to ingested toxins), and other factors, and 2) plastic itself is a major, major problem, and it is gradually being revealed the plastic kills life at all levels, including choking of sea animals and birds, but also breaking down into small toxic particles that are mistaken for food by all kinds of animals, and end up in human bodies (not that we are more important – we are, but it can not be divided in that way).Here is a link to a very thorough and eye-opening article.So, I feel there are other vital factors with plastic bags, such that I feel paper is superior as I have not heard of durability of the toxic effects in the paper cycle.Anyone else have thoughts about this?
Good points, planetthoughts. There’s definitely more to environmental impact than energy. And you point out some of the very legitimate downsides of plastic.Paper bags (like anything) have their own downsides too. Take, for example, this snippet from an NRDC article that’s mostly critical of plastic:”Most of our paper grocery bags originate in one of two places: Canada, where 90 percent of the timber is harvested from old, biologically rich forests, or the southeastern United States, where timber companies are rapidly replacing the region’s last native woodlands with monocultural tree plantations that have as little biodiversity as corn fields.”Then there’s the paper industry itself. To transform virgin timber into paper, manufacturers consume more fresh water than any other industry on the planet, and in return emit significant quantities of dioxin and other hazardous pollutants, according to EPA.”Of course, that’s all harder to quantify & compare with energy and climate impacts.
Where did the canvas bag energy information? It didn’t seem to come from the bag comparison pdf that you linked to. This is great. Thanks for making your findings simple and to the point.
I’ve always thought it would be a step in the right direction if grocery checkers were trained to stop the inane “paper or plastic?” query and instead say, “Did you bring a bag today?”
At a first glance, I found that this article had some useful information especially analytical methodology but there were a few problems with the source of the data that bother me (and were noted at the bottom in geek notes) First off the measure the economic costs of disposal of plastic bags was measured in Australia whereas the study on energy use to produce the bags was done in Europe with a particular emphasis on Sweden. You can’t compare apples and oranges. What should have been done was an analysis of production and waste disposal in the same country as the production. This can be drastically different simply on recycling habits between countries. A more detailed analysis of Australia can be found in these two links:http://www.abc.net.au/science/features/bags/default.htmhttp://www.environment.gov.au/settlements/publications/waste/plastic-bags/pubs/report-2002.pdfAccording to the first site only 10% of australian homes recycle at all and only 1% of plastic bags are reused. I think those statistics are very different in Europe.In addition, I’ve read the PDF article pertaining to the quote of 0.5 MJ to dispose of a single plastic bag and I do not see where this is quoted so disclosing how this figure was calculated would be helpful. What that article does state is that the significant majority of plastic bags goes into land fill so if one were really interested in the economic impact of doing so, an analysis of how landfill (which is not done in any of the above calculations) is managed needs to be done (per country) with the costs of risks such as the problems that arose in Bangladesh with the clogging of the irrigation system. Another statement that particularly bothered me was “From an energy standpoint, using a canvas bag is 14 times better than plastic without factoring in the littering, landfill, recycling, and foreign oil dependence issues with plastic bags.”. How can one do a detailed analysis of energy without factoring the disposal of plastic bag? Again, where is he coming up with these magical number 14? I don’t see that calculation nor the data sources. From everything I’ve read on the use of plastic bags and their disposal (which includes production, landfill etc), putting a levy on the plastic bags may be a good start but certainly not a fool proof solution.In my opinion this is a neatly packaged analysis of the economic costs between plastic and paper bags based on data sources that have nothing to do with each other and figures that do not seem to add up (simply because the two numbers to add up could not even be found in the links provided). I can’t say that this was a particular win for the geek who did this challenge.
Sorry you didn’t like it, Voltaire.A couple of points.1) The .5 MJ figure comes from the linked report. I searched the document for “MJ” and it was the first hit:”The embodied energy in one average HDPE singlet bag, weighing 6 grams, is approximately 0.48 MJ, including the production of the polymer, bag manufacturing and transport.”Note that this is production & transport (which I believe includes disposal—e.g., transportation to a landfill – though they aren’t explicit about this point). The .5 MJ figure in the post above does NOT refer to disposal alone. Generally speaking, life cycle analysis tends to find that disposal consumes relatively little energy, compared to other life cycle steps.2) I’d assumed that the “14” figure came from table 4.4 of that same pdf. But I can’t find the calculation either. When I divide “woven HDPE”—a reusable bag—by “singlet HDPE”, I get a factor of 11, not 14. So I’m not sure where Justin got that figure.3) The real point here is NOT paper vs. plastic. We’re not saying that paper vs. plastic is a settled debate, nor that steps to reduce the environmental impact of packaging is a waste of time. What we ARE saying is that there are other daily choices that are far more significant than paper vs. plastic. And to the extent that we all have limited time, attention, and willpower for such things, we should be focusing on the choices that make the biggest difference. And in our judgment, what you put in the bag is far more important than what kind of bag you choose. If you wait until the checkout line to start thinking about your impact, you’re probably too late.Cheers!
Hmmm…that’s an extremely biased food analysis, and fairly meaningless without acknowledging that there are many ways to produce food. If you’re going to label them Meat and Veggie (which will get nabbed and used out of context) you need to have kept all the other variables the same. For example tropical fruit in the meat one, but only locally produced items in the veggie one is going to make the “meat” look worse, when in fact it’s the distance vs. local issue that’s getting represented.
It’s also really important to start debunking the myth that meat is worse environmentally than grains. What makes meat a disaster is the PRODUCTION method: most of those horrible statistics about the embodied energy of meat is because we feed them grains and soy, which are both environmental disasters to produce.
But cows aren’t grain eaters–it’s cheap, and makes them fat. It also makes them so sick they die from it if they aren’t slaughtered first. Cows are supposed to be wondering around outside, eating grasses, bugs and other leafy things, i.e., cellulose that humans cannot digest, but cows can. 100% grass-fed beef takes cellulose and turns it into food we CAN digest–meat. The input output statistic get reversed. 100% Grass-fed beef has FAR, FAR less environmental impact than does eating soy and grains. (More info: read The Vegetarian Myth, by Lierre Keith.)
And even then, it would be necessary to ask: are we taking about conventional, or organic grains and soy. They are both still worse than hunted and grass-fed meats, but in a short little summary like this which will get quoted all over the place, it’s important to note.
Hi Erica, thanks for your comment.
We’re not arguing that there aren’t better ways to raise meat or veggies to lower their carbon footprint. But as it stands now, with existing systems unlikely to change anytime soon, there are significant advantages to a vegetarian-based diet, at least with regards to carbon emissions.
Speaking of, a new report from the Environmental Working Group shows the climate impacts of different types of proteins.