Monday, 13 February 2017

Are bicycle commuters and gym junkies destroying the planet?

TL;DR
Cycling long distances on a standard Australian diet is worse for the environment than taking public transport or driving a green vehicle. For the average Australian, cycling is roughly 6 times worse in terms of emissions intensity than taking public transport, 210% worse than driving an electric car with a passenger and 32% worse than driving in a standard petrol vehicle with two other people. If you're a raw vegan who subsists entirely on bananas though, you can cycle as much as you like (as long as you don't have a super dooper carbon fibre bike with crazy embodied energy). You're more efficient than a solar powered Tesla with 5 people in it.

However, if you aren't raw vegan, cycle a relatively short distance (e.g. ~1hr per day) and don't eat more to fuel the ride, then cycling has a neutral impact on the environment compared to the average Australian and a positive impact on mental and physical health.

Unfortunately, neutral impact doesn't mean you can get off scot free. The average Aussie's carbon footprint is far past the ecological carrying capacity. If you care about climate change, you need to purchase carbon offsets to mitigate your food consumption.

My point in this article is not that people should cycle less but that we need a price on carbon to help people make more sustainable food choices. If you do a lot of cycling, consider using some of the money you save from not using public transport to buy carbon credits and offset your impact.

Are bicycle commuters and gym junkies destroying the planet?
Cycling to work is traditionally seen as a positive thing to do for the environment. But is it really? If you look at the average carbon footprint calculation, you’ll see that at least 33% of the impact comes from food production. These calculations are typically based on a dietary intake of 2000kcal per day – enough for a sedentary office worker to go for a gentle walk in the park but certainly not enough for a cyclist commuting 10+ km to work each way.



Cycling burns roughly 30kcal per km (depending on the weight/aerodynamics of the bike and the steepness of the route). This means my old 44km commute to work (22k each way) used up 1320kcal bringing up the daily burn to ~3320kcal – 66% more than the average person.

We can therefore assume that my carbon footprint at that point was potentially 33% higher than if I’d taken public transport. With those kind of numbers, it’s probably better to drive than to cycle.

I can hear you saying – “but carbon footprint calculators are such blunt instruments – a vegan who grows their own vegies will be responsible for much less 
CO2e emissions than an uncouth fan of the golden arches who loves to use beef burgers as part of their carbo-loading regime.” This is true. The less animal protein, processing and transport involved in a meal, the lower the CO2e emissions. This rationale is the main reason I was vegan for eight years (see this article for details on why I am no longer vegan).

Regardless of how you spin it, a higher quantity of food still results in higher
CO2e emissions. Eating 3000kcal per day to fuel my exercise habits is in some ways a selfish decision. Sure I get physical and mental health benefits from cycling and running but can I justify that against the increased carbon footprint? If we were talking about a 5% difference in CO2 emissions, I wouldn’t sweat it but given that food is almost always the #1 largest contributor to an individual’s carbon footprint (see http://www.eatlowcarbon.org/ for more), eating more will sabotage any other efforts I make to offset my carbon emissions.

To put it in perspective – we have 100% green power at home, don’t have a car and don’t buy a lot of clothes/other semi-disposables. This means that food is by far my biggest carbon liability.

What can an individual do?
What can one do about it? There are a few options:


1.  Stop doing as much exercise.
2.  Optimise food supply to make it as low carbon as possible.
3. Purchase carbon offsets to make up the difference.

I’ve opted for all three. I no longer cycle an hour each way to work every day partly because of the environmental impact (and also because I don’t want to spend as much of my day on exercise). These days I aim to cycle to work twice a week and average about 10 hours per week of exercise, most of it walking, down from the 25hrs/week of intense exercise I used to do. I opt for low carbon protein options (chicken/kangaroo/nuts) and make a monthly donation to CNCF to offset the remainder.

What can we do as a nation?
It would be interesting to see a policy angle on this as well. Carbon intensive foods have a societal cost. I’d be in favour of a tax on them (it’d probably line up pretty well with the proposed sugar/processed food tax that’s been floated to reduce obesity). This way individuals don't have to spend hours of research figuring out the carbon intensity of their food purchases - they can simply 

Fact Check
Is my analysis above correct? This 2010 article argues that cycling is 10 times more efficient than driving a petrol car. 

Let's look at their calculations:
1. Cycling uses 50 kcal per mile - this is basically equivalent to 30 kcal per km
2. One mile of cycling powered by bananas will consume 65g CO2

To calculation emissions intensity, we'll first look at the volume of bananas required for 50kcal. Bananas have 890kcal/kg according to NutritionData.com. That means you'd need 56g of banana to propel you one mile. Each kg of bananas involves 480g CO2e. Therefore, one mile of cycling powered by bananas generates 26.88g CO2e (which is actually half of what the article states).

Compare that to a car. According to the Green Vehicle Guide, the average vehicle emits 184g CO2e per km or 294.6g CO2e per mile. Therefore it is accurate to say that a banana powered cyclist will be 10x more efficient than the average car.

However, it's safe to say that the average cyclist is not a raw vegan. According to ShrinkThatFootprint.com, the average person's food consumption results in 2.5 tonnes of CO2e based on a daily intake of 2600kcal. That means a daily output of 6.8kg CO2e and therefore an emissions intensity of 2.61g/kcal.

As a consequence, the average cyclist will emit 130g CO2e in cycling one mile.

That's still better than driving the average car on your own but it's worse than ride sharing (e.g. if you share a ride with two other people, it will be less energy intensive than driving) and it's far, far worse than public transport. According to the Australian Climate Council, public transport on average results of emissions of ~22g CO2e per km or 35.2g CO2e per mile. Electric vehicles also quite good at around 4g CO2e per km (assuming they're powered by renewable energy) plus 85g CO2e per km in embodied energy or 136g CO2e/mile.

Other considerations

Cycling short distances
As my friend Rachel Bunder pointed out, this analysis only holds true if you eat more as a consequence of cycling. If you cycle a relatively short distance (e.g. 20k/day), you probably won't have to eat more to fuel the ride and the environmental impact will be neutral (though your underlying footprint will still be highly influenced by your diet).

Embodied energy of electric vehicles
According to this study, electric vehicles have embodied energy GHG emissions of ~85g CO2e/km.

Embodied energy of bicycles
Have been unable to find stats on it but one would assume that a high tech carbon fibre bike would have relatively high embodied energy and this would remove the green tinge from a raw vegan cyclist.

Health impacts of not cycling as much
Please don't stop cycling as much after reading this article. My point is not that you should stop cycling but that if you do a lot of exercise and eat a lot, then you should probably offset your emissions by purchasing carbon credits.

Decreased health almost certainly involves high energy usage. Those ER heart zappers need a fair bit of electricity after all!

Capacity impacts of cyclists moving to public transport

In Australia, this would probably have a negligible impact given the comparatively small numbers of bicycle commuters but in other countries this would be a problem. Again, please don't stop cycling, just buy carbon credits if you use a lot of energy from your bike commute.

What if I'm a more efficient cyclist?
30 kcal per km is relatively high. A fit cyclist might be down around the 20kcal per km mark. Factor that into calculations of your impact.

What if I don't eat more as a result of cycling?
It doesn't particularly matter. GHG emissions from food consumption are unsustainable for people who follow a standard Australian diet. My personal footprint (based on 2000kcal) requires 1.2773 earths to produce enough food for me to survive (and another .9 planets for the other requirements). If you care about your impact, you need to purchase carbon offsets to mitigate your food consumption.

Similar work
http://keith.seas.harvard.edu/blog/climate-impacts-biking-vs-driving

2 comments:

Rob said...

Thanks Jeremy, the calculation is very interesting and it's good to be debating these issues. To me though the implied conclusion that we should all get in our cars is flawed because regular exercise is not only a right but also essential for our health and wellbeing. With this in mind:
- Your calculations would apply to ALL exercise, including going to the gym, playing soccer, tennis, running etc. So actually bike commuting is a very carbon efficient way of getting exercise in your day because the carbon cost is 'offset' by not having to use the car. The most inefficient option would be to drive to work & back and THEN go and do a large amount of exercise. So perhaps tell everyone to stop playing soccer & tennis, but cycle to work instead?
- It argues that living far from work, school etc is carbon costly either way, so you could also make this into an argument that people who live far from work, school etc are the ones who have the biggest carbon footprints regardless of transport mode
- Overall it highlights the very high energy costs of food production and how much non-renewable energy this uses, which is a very real issue

FWIW I'm also not really convinced people doing regular exercise do actually eat more! Is there a way you can fact check this? It would be interesting. A year ago I was doing no regular exercise, and now I'm cycling 200km a week. But I honestly don't think my overall food intake has increased.

jeremy nagel said...

Hi Rob,
thanks for raising those points. I've revised the article to clarify my stance. I agree that food production is the real issue here and I don't mean to demonise healthy exercise.

RE food intake not increasing despite exercising more: it doesn't really matter. 2000kcal of a standard Australian diet is already unsustainable.