On why we should continue to buy food wrapped in plastic

Categories: The Great Plastic Debate

Published: 8 May 2018

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(Featured image: by Marco Verch, CC BY 2.0)

In a recent post I discussed why wrapping fruit and vegetables in plastic is a good thing because it slows biological decay, and therefore prolongs shelf life and minimises food waste. This turned out to be a spectacularly unpopular thing to say, and it seems that a significant number of people think that plastic waste is more important than food waste. Consequently, this post is going to try and put some numbers on the relative importance of packaging and food. How big are the environmental impacts of food production and food waste compared to those of packaging? There are obviously some trade offs here; if a particular food is very resource intensive to produce, then packaging with high environmental impacts could be regarded as reasonable in order to keep the precious resource in good condition.

I’ve written this very much in the context of our current supply and distribution system, which has to keep food fresh for weeks or even months at a time. Any keen veg grower will know that food is best eaten as soon as possible after being picked, indeed this is a major reason why many people choose to grow at least some of their own fruit and vegetables. Where we can’t do this, the second choice might be fruit and vegetables in season from a local farm shop or market. Short supply chains can allow food to be kept fresh without a lot of packaging. However, the fact remains that most of us rely on supermarkets for at least some of our fruit and veg, and if we want to eat anything out of season or food that isn’t grown in the UK it is likely to need packaging in order that the product gets to us in good condition.

In the long term, reducing the resource intensity of food production and shortening supply chains so that food didn’t need to be preserved for so long are better options, but require societal level adjustments in attitudes to food and farming. In the mean time, should we have shrink wrapped cucumbers and buy our bananas in plastic bags? In order to get some idea of this we need to think about the impacts of 4 things:

1. food production
2. food waste
3. packaging production
4. packaging waste

1) Impacts of food production

Agriculture’s total contribution to climate change depends on what you count. Directly, it contributes around 14% of total GHG emissions at a global level, with land use change contributing another 19% (this number comes from WRI, and if you’re a data geek, this source allows you to look at global emissions in all sorts of different ways). Much land use change is deforestation carried out to increase available agricultural area, so it’s not unreasonable to consider most of this 19% as part of the problem of agriculture. Agriculture’s role compared to other sectors is shown in the Sankey diagram below. These numbers from WRI are similar to estimates from other sources, which suggest 19-29% of global emissions can be attributed to agriculture (with much of the variability in estimates relating to how land use change is treated).

Sankey diagram of primary sectors responsible for GHG emissions (left side), intermediate sectors (middle) and final GHG emissions (right side). Reproduced from World Resources Institute. On the left hand side we can see that our GHG emissions result largely from our need for energy, with food/land use change being the majority of the remainder. The central portion of the diagram shows the activities that drive these emissions. The right hand side shows the end result in terms of the various greenhouse gases. We can see that agriculture is responsible for the majority of the world’s methane and nitrous oxide emissions.

So if that’s the global picture, what about the UK? It’s not easy to zoom in on how these figures relate to UK consumers; we have estimates of domestic agriculture’s contribution to UK GHG emissions (around 10%), but as much of our food is imported it’s difficult to calculate the environmental impact of all the food consumed in the UK. Estimates from here suggest between 15% and 28% of total GHG emissions in developed nations. For the UK, that’s 75-140 million tonnes CO₂ equivalents.

2) Food waste and its impacts

Sadly, much of the world’s food is wasted; the FAO estimate that it’s about 1/3 of total agricultural production. There is a readable report on global food waste and where it occurs in the food supply chain here. Broadly speaking, in developing nations, there is considerable loss in the upstream elements of the supply chain because of lack of infrastructure for harvesting, preserving and transporting food. In developed nations, the majority of waste is further downstream. For the purposes of this blog, we’ll limit our consideration to the EU, although you should bear in mind the potentially much higher wastage upstream in the supply chain if you’re buying food originating from futher afield.

Below is a pie chart of food waste by sector in the EU. The data is from the EU-FUSIONS project, which developed a standard method for measuring and reporting food waste across all EU countries, in support of the EU’s aims to reduce food waste by 50%. As you can see, we as consumers are the biggest source of food waste, and are responsible for 53% of total food waste, whilst farmers and retailers waste surprisingly little. If you read the report, you’ll see that there is considerable uncertainty relating to waste from on farm production, where only 6 countries were able to supply reliable data. It’s also likely to be highly dependent on the type of crop, vary from one season to another, and fluctuate according to demand, so we could also argue that agricultural production is a sector where an average is not a particularly useful number.

Food waste by sector across the EU. Data from EU-FUSIONS.

Pie charts are great at showing relative importance, but not for showing the scale of the problem (and if the numbers for primary production are inaccurate, then this would also skew the picture above in terms of relative importance). So whilst we all like pie, it’s probably better to simply look at the actual numbers. A data table (again from EU FUSIONS) helps puts things in perspective in terms of how many kg of food are wasted per person.

From this we can see that householders throw away 92kg of food waste per person per year. This seems like a lot, so the next obvious question is how much of that is inedible (egg shells, banana peel etc)? The Waste Resource Action Programme (WRAP) have done a lot of good research on food waste in the UK, and their data on this suggests that about 22% of consumer food waste is inedible. There’s an intermediate category of possibly edible (parts that some people eat but others don’t, such as  potato skins, bread crusts) that accounts for another 18% or so, but the bulk; around 60% of food that is wasted in the home is edible. And yes, collecting this data did require WRAP to comb through a lot of people’s bins. We have no particular reason to believe that the UK is much better or worse than the rest of the EU, and exactly why it is that we as consumers waste so much food is something I may come back to in a future blog. The GHG emissions arising from the 4.4 million tonnes of avoidable consumer food waste in the UK each year are estimated to be 19 million tonnes of CO₂ equivalents according to WRAP (this is the same as around ¼ of private car journeys undertaken in the UK annually).

3) Impacts from packaging production

I’ve written a whole post about plastic packaging which is here. For the current discussion, we need some idea of the climate change impact of packaging. We can get a basic idea from the Sankey diagram above, which gives the impacts from chemicals as 4.8% total GHG emissions. It’s less easy to say what proportion of these chemicals would be used to create plastic packaging. But it is clearly small compared to the GHG emissions from agriculture. A much better way of looking at the problem might be to do a bottom up calculation, limiting our consideration to plastic. 40% of plastic produced in the world is used for packaging, and 50% of packaging is for food. Using figures from here (GHG emissions of around 1.5 tonnes CO₂e/tonne HDPE produced) and here (3.7 million tonnes plastic used in UK/year), we could make a rough guess that the CO₂ emissions associated with production of plastic packaging for food are around 1.1 million tonnes/year in the UK. I don’t think this is a particularly accurate number.

4) Impacts of plastic waste management

We’re going to limit this discussion to greenhouse gas emissions. Whilst some readers undoubtedly care passionately about marine plastic pollution (which I have written about here and here) we could just as well argue that we have missed out important impacts of agriculture; nitrification of the marine environment for example, or eutrophication. And since the original question posed was deciding on the importance of food production/waste compared to packaging, we need impacts that are applicable in both sectors, hence limiting the consideration to GHG emissions.

This report by WRAP analysed a range of life cycle assessment studies on municipal solid waste, and recycling plastic was beneficial from a GHG emission perspective in every study when compared to landfill and waste-to-energy. However, the benefits are highly sensitive to the assumptions made about how much virgin plastic production is displaced by recycling; if 1 unit of recycled plastic displaces 1 unit of virgin plastic, recycling is a good option. If the displacement falls below around 70% substitution (because the recyclate quality is too low to make a sufficiently high quality new product), then recycling was no longer justified. This is an extremely difficult problem in the UK and elsewhere; post consumer plastic is collected mixed, and significant investments in sorting equipment would be necessary to generate good quality recyclate. Perhaps this will happen, given the level of public interest in plastic at the moment.

However, if we were to take a perfect recycling scenario, a tonne of recycled plastic saves about 500kg CO₂ emissions, compared to the production of a tonne of virgin plastic. Accounting for the GHG emissions of waste management is highly dependent on the assumptions made in the counterfactual; what would happen to the waste if we didn’t take a particular course of action. If we don’t recycle plastic waste we have a choice between landfilling it and incinerating it. We could argue that landfilling plastic is an excellent idea; it is a very stable material, made from fossil fuels, and so burying it in the ground is sequestering carbon. This might also give us a ‘mine’ of future material which we can extract once our processing technologies have advanced sufficiently. We could also say that incinerating plastic to create heat and electricity displaces electricity production via other means. Whether or not this has GHG emissions benefits therefore depends on what other source of electricity generation is being displaced. I might come back to this complexity in a future blog post, but in the mean time, we can use the numbers from the WRAP report that indicate around 0.1 tonnes CO₂ emissions from landfilling 1 tonne of plastic.

The final reckoning…

We now have the following numbers for the four impacts we were originally interested in when we were thinking about the relative importance of food and packaging.

This are plenty of flaws in how I got to these numbers, and it’s also an average situation. But hopefully it will be clear that overall, the GHG emission impacts of agriculture are at least 100 times higher than the impacts of the packaging we use to keep food products fresh. So we should remember that food is precious and minimise our purchase of food we don’t then end up eating. We should also ensure that it is kept in such a way as to ensure it doesn’t go off before we eat it. In most cases this means packaging and keeping it in the fridge, as discussed in a previous blog post here. If you want to read about why in most cases the best packaging material is plastic, the blog post is here.

Averages – always wrong but often useful

As I’ve pointed out, I’m not confident in the accuracy of the numbers calculated above, but since the magnitude of the difference between agriculture and packaging is around 100, perhaps we can take them as indicative of an overall picture.

The issue of GHG emissions from food and what it’s packaged in has also been studied directly for individual foodstuffs (including for packaging materials other than plastic), including by a group at the University of Michigan. If you’re interested in the detail, two key reports are here and here, and yet more details are available via this website. For the current discussion, two summary diagrams are worth highlighting. The first one emphasises the overall carbon footprint of food, and how small a part packaging plays in this.

Carbon footprints of food production (orange), processing (blue) and packaging (green) for a variety of food categories. From Heller (2017).

If you’ve read my blog post on what a low carbon diet might look like (here) this data isn’t very surprising; meat production (particularly beef and lamb) has very high GHG emissions. Consequently, the GHG impacts of anything that the meat is packaged in are going to be very small in comparison. Whilst this data only covers impacts up to the point of use (i.e. the impacts of food you throw in the bin isn’t included), it obviously follows that it’s particularly important not to waste foods with high carbon footprints (or just stop eating them).

The second stacked bar chart (below) includes impacts across the entire life cycle, and is based on data from the US.

GHG emissions across the life cycle for a range of food products. The values above each stacked bar are the total GHG emissions (kg CO2 e) for 1kg of the product. We can see that for the vast majority of foodstuffs, the GHG impacts of food production and processing (pale blue) are larger than any other part of the life cycle. From Heller & Keoleian (2017), p51.

The pale blue part of the stacked bar is food production and processing. Spinach is the only product for which packaging was significant, and you’ll note that the packaging type (PET clamshell) is not what’s generally used in the UK (where ready to eat bags are more common) so it’s not clear how applicable this finding is. The pale green part of the bar is packaging production, and is not a high proportion for most foodstuffs. Similarly, the proportion of emissions from packaging waste disposal (the dark green part of the bar) is invisibly small for most food stuffs; from a GHG emission perspective, what you do with plastic waste is insignificant. The dark blue part of the stacked bar (edible food waste disposal) reiterates the significance of food waste which we looked at earlier.

Bear in mind that because the total impact of each food stuff has been normalised (i.e. the bars are all the same height) the potential for misinterpretation arises; even though packaging is a significant part of the impact of spinach, if you are a meat eater, spinach packaging is trivial. Please dwell on that point for a moment if you eat meat (and I am a meat eater myself).  The value above each bar is its total GHG emissions per kg of product if you want to be reminded of the relative impacts of different foodstuffs, and go back to my blogpost on low carbon diets if you want to understand this aspect better..

Final thoughts

Food production makes up a significant proportion of global GHG emissions. Plastic packaging doesn’t. Even if we are more concerned with waste management than climate change, food waste is still far more signficant than plastic waste. We cannot expect to eat fruit and veg that is out of season in the UK and/or not grown here at all and simultaneously not want it to be packaged like the precious commodity it is. We also need to stop buying food we don’t eat.

I find it both depressing and fascinating that I ended up feeling I needed to write this post. Depressing because despite the overwhelming maths, our society seems to be obsessed with drinking straws, plastic bags and disposable coffee cups, rather than what is undoubtably the biggest environmental challenge we have ever faced, namely GHG emissions. Fascinating, because I really don’t understand how we got ourselves into this mess.