It was a month ago when I heard the surprising news that milk packaged in cartons has the best environmental performance as compared to other packaging materials. Do they, really? Aren’t the reusable deposit bottles world famous for being green? Well, actually, milk bottles are white or brown, of course, but environment-wise their reputation is outstandingly green. In order to find some reliable information, I took the time to scan two comparative LCAs on beverage packaging, and guess what: the returnable glass bottle is far from being the best. LCA, for those who aren’t familiar with the initials, stands for life cycle assessment, a normed process for finding out all environmental effects a product generates: from raw material extraction, to production, to transport, to consumer, to disposal. The first LCA compared cartons with single use PET and HDPE bottles, the two main plastics used to package milk.
A recent, Europe-wide Life-Cycle Assessment, conducted by the Institute for Energy and Environmental Research (IFEU), for SIG Combibloc has confirmed that, compared to disposable high-density polyethylene and PET bottles, carton packs for UHT milk have a significantly better environmental profile—particularly with respect to CO2 emissions, use of fossil resources, and consumption of primary energy.
In the 1-L format, carton packs generate 34% less CO2, use 56% fewer fossil resources, and consume 30% less primary energy compared to HDPE multilayer bottles; when compared to disposable PET bottles, these figures are 45% for CO2, 57% for fossil resources, and 36% for primary energy.
To make things easier to compare, the only impact category I focus on in this article is climate change. Environmental performance is not only about climate related carbon emissions, of course, and some packages might score better in terms of water use or ecotoxicological potential, for instance. LCAs are precise, they consider all kinds of impact categories. However, I chose to compare only the carbon emissions from different packages. I beg your pardon for that; it is, however, more comprehensible.
The carbon emissions of a milk carton, so says the paragraph cited above, are 45% less than the ones of a PET bottle. In absolute terms, the life of a milk carton is responsible for 85 grams CO2 equivalent. The comparable PET bottle lives a different life and emits 155 grams. Same for the HDPE bottle, which releases 129 g CO2eq. How does that compare to other packaging materials? Is the carton really the green darling of the packaging family?
Let’s take a look at another comparative LCA. The British NGO and recycling promotion organization “WRAP” (Waste & Resources Action Programme) compared the most common types of milk packages on the UK market in January 2010. First of all, it has to be said that on their island, the British can be funny sometimes. Unlike the rest of Europe, they don’t stick to the metric system across different packaging materials. But the cartons, at least, adhere to the 1L size.
Carbon emissions for one functional unit of 500 2-pint-HDPE-bottles
In contrast, glass milk bottles come in the one imperial pint (0.568 L) size, and HDPE bottles come in the two imperial pint (1.136 L) size. To compare different sizes, every LCA defines a functional unit. In this case, the study’s functional unit depends on the container type. To match the volume of 1000 1-pint-bottles, you take 500 2-pint-bottles or 568 1-L-cartons. This is important in order to calculate comparable emissions for individual packages.
Turning a blind eye to the 0.136 L difference, let’s start with the HDPE bottle. A 2-pint bottle made of 100% virgin HDPE (i.e., non-recycled) causes 136 g CO2eq if the bottle is incinerated after use (68kg per functional unit divided by 500 gives 136 g for one bottle). This number is fairly close to the 129 g result of the first study – laurels to the LCA methodology! In a theoretical condition of recycling the bottle after use, the emissions decline to a promising 64 g. But that is only theoretical.
The race for the best packaging is still not finished. So far, the Combibloc carton is first, with 85g CO2 eq, overtaken only by the ghost of a to-be-recycled 64g-CO2eq HDPE bottle.
The other packages analyzed in the LCA were two types of 1-L-carton and a returnable one-pint glass bottle. To cut a long story short, the carton with a screw-cap caused way more emissions (64g CO2eq, p. 64) than its little brother with a gable top (only 47 g!) due to the plastic required for the cap. Is this tiny gain of convenience really worth 17 g of extra emissions per carton? If you look at the following two images, you’ll know what I mean.
Carbon emissions for 568 gable-top milk cartons, 1 L (that is one functional unit which equals 1000 1-pint-glass bottles)
Carbon emissions for 568 1-L-cartons with plastic screwcap, p. 79 of the PDF
What’s more important is the announcement of a new leader in our carbon footprint race: the gable top carton! At only 47 grams of carbon equivalent emissions, that’s magnificent! Can the famous glass bottle beat that?
Basically, it all depends on distribution distance. How far away from each other are the factory, point of sale and point of consumption? The high weight of glass causes significant transport emissions, as you can see in the following image, taken from page 90 of the PDF.
Carbon emissions for 1000 Glass bottles of 1 pint
The emissions are hard to compare, since this is a 1-pint-bottle (Remember? 1 pint = 0.568 liters). Multiplying the emissions in order to retrieve a 1-L equivalent won’t produce a satisfying result since the ratio of contents to packaging material rises with increasing container size. However, looking at the study’s best-case scenario for glass – bottle-to-bottle recycling as the waste management option and 60% recycled content in the glass – 36 grams CO2eq for one pint are quite a lot compared to the saint-like image these bottles generally tend to have. On the other hand, emissions drastically decline with lower transport distances. If you live near a bottling plant, you should consider returnable glass as an option. Not to speak of the unbeatable look and feel of a traditional glass bottle. But that’s another story.
