I’ve written a post showing you how individual choices affect global warming. You should read that instead. This is a dry, technical supporting post showing you where the numbers come from. If you read it, please read it after my post on methods. For reasons given there, I’ll be relying a lot on a book by Mike Berners-Lee for emission intensities of actions, although every figure will be cross-checked against other sources.
Transporting, sorting and processing recycled things all emit greenhouse gases; those have to be balanced against the emissions from creating new things. So it takes careful analysis to tell whether recycling actually reduces emissions.
Unfortunately, the research on net emissions from recycling is so sparse as to be frustrating. I’ve hunted hard and only found one paper using input-output analysis. It has the following wonderful quote:
It is important to remember that the recycling of waste materials is not an aim in itself, but a means of reducing the overall environmental load resulting from waste emission, and that any production and consumption activities, including recycling and waste treatment, also emit waste.
This is a simple point, but it’s hard to convey to people, because recycling feels so ‘green’. Before diving into the paper, I want to do some back-of-the-envelope calculations for the UK, to give us a sense of scale.
An upper bound: what can be recycled?
The graph below is from Berners-Lee, and explains how emissions per person break down in the UK. Have a read of the labels. As far as I can see, the only things that can be recycled by individuals are ‘other non-food shopping’ (7% of emissions) and possibly the packaging from ‘food’ (25%).
Let’s deal with the food packaging first. As a very, very rough rule of thumb, most things have a few kg of emissions per kg of material. (You can check that for both food and plastics by looking at Berners-Lee.) This means, very roughly, that the emissions from producing things are in proportion to their weights. Food packaging usually weights a lot less than food — think about the weight of your food shopping if you took out all the food — so we’d expect packaging emissions to be much less than food emissions.
And indeed, Berners-Lee’s emissions figures for takeaways say 2.5% come from clear plastic trays. Combining that with the 25% of emissions from food, I’d expect food packaging to be less than 1% of our emissions.
That means food packaging and non-food shopping should come in at under 8% of our emissions. That’s the most we could hope to save by recycling. That’s to say, if:
- We could recycle all non-food shopping
- The recycling process had no emissions
- Each 1 kg of recycled stuff displaced 1 kg of new stuff we would have made
then we could reduce our emissions by 8%. We could say 8% is an upper bound on possible emission reductions. In reality the figure will be significantly lower, as none of those assumptions will be true.
Let’s try to get at this another way. I’d say that a lot of what we recycle is packaging. This estimates 2.4 million tons of plastic packaging was placed on the UK market in 2017. That’s about 36kg per person. Here’s Berners-Lee on the emission intensities of different plastics:
At about 4kg of emissions per 1kg of packaging, that’s around 140 kg of emissions from plastic packaging. Compared to the annual UK emissions of 13 tons per person, we see that about 0.1% of our emissions come from plastic packaging. So there is no way we can save more than that by recycling plastic packaging; indeed, emissions during the recycling process, etc., mean the actual figure will be lower.
What about other kinds of packaging? This table gives a breakdown:
Berners-Lee says printed virgin paper works out at 2.5–3kg of emissions per 1kg of paper. Working through, we find that’s about 200kg of emissions per person, or about 0.15% of our emissions for paper packaging. For steel he estimates 1.8 kg of emissions per 1kg of steel, which is negligible at only 0.01%. (Remember that’s for steel packaging. Steel in other things is a lot more.)
For wood, aluminium and glass Berners-Lee doesn’t give figures. This is just a rough calculation, so I’ll use Wikipedia to get emissions per 1kg material of 0.46 for wood, 8.24 for aluminium and 0.85 for glass. Plugging those in I find wood packaging is negligible and aluminium and glass packaging are each around 0.02% of emissions.
I was surprised that the aluminium figure was so low, so I obtained independent estimates of 207,000 tons of packaging times 13.5 tons of emissions per ton, giving 0.03% of emissions. Truncation error during lifecycle analysis might mean that figure is out by a factor of 2, but it’ll still be a tiny percentage.
So all in all, packaging looks like it only accounts for roughly 0.3% of our emissions. Again, that’s an upper bound on what we could save by recycling packaging.
As I noted, there’s really not much research here. This paper uses lifecycle analysis to determine the net emissions from recycling of source-segregated materials, that is, recycling that has been presorted into plastics, paper, etc.. Here’s the key table:
The dark grey bars on the left are emissions saved by not manufacturing new materials; the light grey bars on the right are emissions from the recycling process. It looks like on average recycling saves 1–2 tons of emissions/ton of recycled material. (Metals are much higher but are a small proportion, so it averages out.) We’ll use that fact later. Here’s a close-up of an interesting part:
Look at paper on the fifth line. You can see that the dark grey bar (savings) is a little longer than the light grey (emissions). So it looks like in total, recycling paper is a good way to reduce emissions. Looks is the key word here. There are two problems:
- Lifecycle analysis is notorious for missing as much as half of emissions. Both the dark grey and light grey bars could have quite different lengths. For many of those items (e.g. paper), it wouldn’t take much mismeasurement for the light grey bar to be the longer one; in that case, recycling would increase emissions.
- Single-stream recycling is the norm in the US and the UK. That is, paper, plastics, etc., are all mixed together. Separating these takes work! And that means more emissions, which are not accounted for in that table. Again, that means that recycling might increase emissions in many cases.
As an aside, that graph also shows that emissions from transporting recycling are negligible; we don’t need to consider them when deciding whether to recycle. There’s a similar graph in Berners-Lee that shows that landfill emissions aren’t a significant factor.
It’s really just the emissions from avoided production that have a significant effect.
I said at the start of this article that there was just one paper that analysed recycling using the robust Leontief input-output method. It looks at Japan, where:
The Japanese government has recently enacted a series of new laws to promote the recycling of used containers and packaging materials, discarded electrical home appliances and construction waste, among others.
It finds that a ‘proper combination of waste disposal and recycling processes’ can reduce CO₂ emissions by up to 2.1%. Given our discussions earlier in this article, it shouldn’t be surprising to see a figure this low.
As I said, there are no other input-output analyses out there, but we should still sanity check 2.1% against something. This analysis says that recycling waste can save 0.9 gigatons of global emissions in 2030, out of 70 gigatons total. That’s 1.3%. Significantly smaller, but same order of magnitude.
So, should we go with 2%? Not quite; there’s one more issue. All these numbers gauging potential emission reductions from recycling have been considering all the waste a society generates. That’s waste from households and from industry. But the individual actions we’re interested in only reduce household waste.
How much of a difference does this make?
Estimates vary a bit, but that source estimates municipal waste is only 14% of overall waste. (Also household waste is only a part of municipal waste, but we’ll assume you can recycle at work if you want to.)
I must admit to being somewhat frustrated at this point. The lack of reliable research makes this whole exercise like playing pin-the-tail-on-the-donkey. I’m going to give you a couple of datapoints and then a guess.
- The Japanese paper includes an analysis case excluding construction waste, and only finds emissions reductions of 0.7%. The details of that case are quite different to ours, though.
- This estimates 2 kilograms (4.51 pounds) of municipal waste per person in the US. That’s about 0.7 tons a year. We estimated earlier that recycling saves around 1–2 tons of emissions per ton of recycled material, so 0.7–1.4 tons a year. That’s 0.3%–0.7% of emissions for an average person in the US.
- We saw above that municipal waste is around 14% of total waste. Earlier we estimated all recycling, including industrial, could reduce emissions by 2%. Combining these suggests recycling municipal waste could reduce emissions by about 0.3%.
I’m going to grit my teeth and go with 0.5%. The real figure could be a lot lower or a little higher; it seems very unlikely that it would be more than 1%, though.
Combining these with Berners-Lee’s figures, we find these figures for 100% recycling:
- An average person in the US could reduce emissions by about 0.11 tons a year by recycling everything possible; that reduces 2100 temperatures on the Little Planet by about 0.012 °C.
- An average person in the UK could reduce emissions by about 0.065 tons a year by recycling everything possible; reduces 2100 temperatures on the Little Planet by about 0.007 °C.
To put that in context, the UK figure is very close to the emissions from an annual return trip from London to Glasgow. By train.
All the research I can find considers recycling being done locally, with proper procedures. That’s not what happens in the real world. A lot of recycling is exported to developing countries. Until recently, China was the main importer, but it banned waste imports in 2018. Here are the main destinations for US plastic recycling:
The article that’s from says 20% to 70% of plastic entering recycling facilities around the globe is discarded because it is unusable. But discarded waste doesn’t just disappear; it has to go somewhere. The countries that import recycling generally have much worse waste management practices than in the US or EU. I used this data to find the proportion of waste that’s inadequately managed in each country in the image above:
What might it mean if your plastic recycling is inadequately managed? Well, it might be incinerated on open rubbish dumps, releasing toxic fumes. Or it might end up in the ocean; you can see Bangladesh, Thailand, Vietnam, the Philippines, Malaysia and Indonesia in the image below.
You can of course look into your own local recycling operation; if you’re lucky and everything is done locally, you don’t need to worry about this. If not, you’re likely to do more harm than good by recycling plastics. (I wrote more about the impact of plastic bags here if you’re interested.)
I can’t find good sources on other kinds of recycling. It’s probably safe to recycle things with high metal content, as those are valuable and likely to be recovered wherever they end up, but I’d check your local operation before recycling anything else.