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news
Steaks courtesy http://pdphoto.org/Cycling can contribute more to global warming than driving, argues Harvard researcher
One argument sometimes used to counteract accusations that cyclists “don’t pay road tax” is to point out that even if vehicle excise duty applied to people on bikes, they would pay nothing, just as drivers of the least polluting motor vehicles do.
The common assumption underpinning that is that someone pedalling a bike must by definition produce lower emissions than any motor vehicle.
But a climate change researcher at Harvard University’s Keith Group has challenged the idea, and says that some cyclists may actually be more harmful to for the environment than some cars.
Specifically, graduate student Daniel Thorpe singled out cyclists who follow the Paleo Diet, which have menu plans that are focused heavily on meat and animal protein, as contributing more to global warming than someone following a different diet who drives a fuel-efficient, low-emission vehicle.
His detailed findings are in published on the Keith Group’s blog on the Harvard website. He starts by noting the energy required to power a bike – 0.2 MJ/km against a typical car driven in the US, 3.3 MJ/km, and a Toyota Prius 1.7 MJ/km.
Thorpe’s hypothesis instead uses a measure called carbon dioxide equivalents (CO2e) which enables scientists to provide a like-for-like measure of different kinds of gases based on their “Global Warming Potential” (GWP) and thereby gauge the environmental impact of complex scenarios, such as here where both mode of travel and type of diet are being compared.
As an example, 1 gram of methane, associated with livestock, is equivalent to 300 grams of carbon dioxide in terms of global warming potential, giving a reading of 300 gCO2e. Nitrous dioxide, also a factor in agriculture, has a value of 30 gCO2e. Thorpe writes:
This doesn’t matter a lot for estimating the impact of cars, where 90+% of the emissions are CO2, but it does matter for the agriculture powering a bike ride, where there are substantial emissions of N2O and CH4, which have GWP’s around 30 and 300, meaning we usually count 1 gram of CH4 emissions as equivalent to ~30 grams of CO2 emissions.
By Thorpe’s calculations, typically a car in the US will emit 300 gCO2e per kilometre driven, while a Prius emits 150 gCO2e/km. Based on average daily calorie intake of a cyclist in the US of 2,600 kcal/day he says the typical cyclist will have a reading of 130 gCO2e/km.
Someone following the Paleo Diet, however, will emit 190 gCO2e/km, “likely higher than the Prius, though the uncertainties in these estimates are large,” admits Thorpe, who adds that a vegan’s emissions will be much lower at 80 gCO2e/km.
The researcher said that his calculations suggested that two cyclists following the Paleo diet would actually do less damage to the environment than if they car-pooled.
He acknowledges that there are some qualifications, writing:
The first is that we found biking to have a surprisingly similar impact to driving on a per kilometer basis. But of course, cars enable you to travel much faster and much farther than bikes, so someone with a bike and no car almost surely has a much lower impact by virtue of covering a lot less distance. When I owned a car in rural Virginia I drove 20,000 km/yr, and now that I only own a bike in urban Cambridge, Massachusetts I bike about 1,500 km/yr.
The other qualification is that while GWP is based on a 100-year cycle, the period of radiative forcing of individual gases differs; 10 years for methane and 100 years for nitrous dioxide, but millennia for carbon dioxide.
That means that while nearly all of the impact of methane and nitrous dioxide is captured in the GWP calculation, it “ignored hundreds of years of CO2’s influence after this century.
“There are reasons to think we should care more about short-term warming, since we’ll have an easier time adapting to slower changes farther in the future, but it seems odd to completely neglect everything more than 100 years away,” Thorpe argues.
He concludes that “agricultural impacts on the environment really matter,” and that “biking has a surprisingly similar impact to driving on a per kilometre basis, and depending on your diet can cause noticeably more emissions and land use.”
He adds: “Our analysis certainly doesn’t prove that you shouldn’t do more biking instead of driving, but it does help us know more clearly the environmental impacts of making the switch.”
Simon joined road.cc as news editor in 2009 and is now the site’s community editor, acting as a link between the team producing the content and our readers. A law and languages graduate, published translator and former retail analyst, he has reported on issues as diverse as cycling-related court cases, anti-doping investigations, the latest developments in the bike industry and the sport’s biggest races. Now back in London full-time after 15 years living in Oxford and Cambridge, he loves cycling along the Thames but misses having his former riding buddy, Elodie the miniature schnauzer, in the basket in front of him.
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Just sent the email below to David Keith, head of the Keith group which published this research.
"Dear David,
having an environmental degree and an MSc in Transport Planning, I have to say I was amused by this piece of research, which is so full of holes it could serve as a collander.
"Paleo-diet cyclists warm the planet more than Prius drivers -- but under the usual (but crazy) assumption that nothing matters beyond 100 years in the future"
That is far from being the only crazy assumption; perhaps you might like to read some of the comments on the road.cc website -
http://road.cc/content/news/193523-cycling-can-contribute-more-global-wa..."
I'll post any responses here.
Cyclists have a huge Co2, all those post office van deliveries for kit, gear and gadgets
The study is nonsense based on my own experience. When I cycle more I actually eat less. All midweek rides are done fasted on water. I'm not on the paleo diet and none of the cyclists that I know are. 50 kcal per Km, and this is the work of a qualified researcher. The average cyclist working at a tempo pace would be using more like 30-40 kcal per mile (ie 30-40 per 1.6km or 18.75 to 25 per km) meaning this learned fellow has overestimated calorie use by at least double. In addition the recent emissions scandal has highlighted that no production cars are close to test emissions under real world conditions.
How to fund a research grant.
1. Have a theory.
2. Design your experiments to fit your theory.
3. Get Degree/PhD/whatever.
And before you moan at my very simplistic rubbish.
1. I'm taking the Pee
2. I spent the first 22 years of my working life in R&D.
Twonk!
Since I can't be arsed to redo his calculations I'm going to make the dodgy assumption that they're somewhere near OK.
Stacking up the dodgy assumptions, this site http://thepaleodiet.com/the-atlanta-journal-constitution-qa-with-dr-cord... suggests the number of people on a Paleo diet is 'in the millions' (presumably worldwide). Let's be generous and say 5m. Out of a global population of 7.3bn. So about 0.068%, or about 1 in 1500. How many people cycle? Random guess - 20%.
So 1 in 7500 cyclists are Paleo.
Wiki says 0.1% of cars are plug in, let's be really generous round that up to 0.5% to include hybrids.
Basically the 'worst' 1 in 7500 cyclists cause more emissions than the best 1 in 200 cars.
Whilst I have not read the study in detail, I would question the figures for CO2 from the Prius. Whilst it might be able to run on 150 gCO2e/km would it be able to achieve this efficiency in doing a cycle of 2km journeys rather than long trips on trunk roads/motorways?
Nobody in the cycling lobby would advocate for all journeys to be undertaken by bike and no-one in the car lobby believe that cars are as efficient as the published industry figures suggest.
Cars and bikes are very different. It is at the extreme end of the cars usage ie. very short journeys that the bike lobby would like to see less car usage. To be meaningful the motoring figures need to be relevent at this profile and I suspect the Prius would be much more inefficient and cyclists would not need specific diets to manage them.
My whole beef (yes, pun intended) with this finding is that the low-carb Paleo diet isn't exactly ideal for an activity as energy-intensive and as heavy on endurance as cycling.
On the outset, at least, high-carb vegan diets look better suited to cycling than Paleo is.
Then again, what do I know...I'm just a "dumb cyclist"
Depends on the category of cycling (meaning avg speed and distance). What for convenience I'll call "utility cycling" would be journeys of up to 10km under an avg speed of 20kph, and like walking shouldn't need any dietary consideration. Whatever the diet, no one will exhaust their glycogen at that distance unless they've got a medical condition.
The thing is, although he defines specific types of car use (a prius, carpooling), he doesn't define the cycling beyond the diet. Of course energy use in cycling varies massively as air resistance rises to the square of velocity (not quite as simple as that at cycling speeds, but it'll do). I assume he's referencing sports data, which would explain why his numbers are so off compared to other sources.
Basically, it's a complicated way of saying the following. Something that is energy efficient can still produce more CO2 than something that is less efficient, if it uses an energy source with high enough CO2 emissions.
To whch I would add "duh".
Leaving aside some other side effects, some low carb diets can help with endurance (not necessarily ketogenic diets), but are generally ill-suited to shorter, peak intensive efforts where the superior energy conversion of carbohydrates is usually a better bet.
There is a logical flaw in Daniel Thorpe's argument is that he is comparing the energy consumpion of the human cyclist to the motorised vehicle which is a fallacious.
The challenge is which which has the higher carbon footprint, (cyclist + bicycle) or (driver + car).
Just like journalists reporting crashes, Daniel Thorp's car seems to be driverless. It's not, and it's a big assumption that the difference between the cyclist and the drivers food consumption will be greater than the cars carbon footprint. He hasn't shown that.
Also missing from Thorps argument is type of journey, which for some a cyclist only needs only one journeys which if done by car needs two or more (think school run, taxi journey etc.)
Thorpe's argument seems to be just too full of assumptions. I think I'll go Occam's razor on this one.
Even if driving was clearly more CO2 efficient, the fossil fuels are a limited resource, whereas farm produce is renewable.
While the study appears to be taking into account the average 20 mile commute, are they including the two or three stops for food or over priced coffee along the way?
The wording of the study though from the outside appears to point to the majority of cyclists being on the Paleo diet. A quick google gives this definition...
a diet based on the types of foods presumed to have been eaten by early humans, consisting chiefly of meat, fish, vegetables, and fruit and excluding dairy or cereal products and processed food
Now nowhere within this do I see any mention of cake or coffee, both staple foods of cyclists. For those reasons im rejecting the findings within this study.
To be fair I don't think this research is as bad as people are making out.
It does not need to factor in the food eaten by motorists as it only studies the extra calories required to power the bike.
Obviously the environmental impact of manufacture is not included but overall the findings seem reasonable.
There are of course many other benefits to cycling in terms of mental and physical health, reduction in particulate pollution and reduction in harm caused by accidents but
for those of us who cycle for environmental reasons I think it gives us a lot to think about in terms of diet choices.
I think the study is very suspect. Why concentrate on a Paleo diet rather than looking at typical cyclists' diets vs typical motons' diets?
I'd suspect that on average cyclists are fitter/healthier than car drivers. This would most likely affect their diet choices (e.g. the car driver rolling round to the drive-in McBurger and the cyclist munching on organic artisanal carrot sticks) but would also affect their resting heart rate. This could easily skew the results the other way as the moton is performing heavy mouth breathing all day long whereas the cyclist just merely sips at the air in the most efficient method possible. (This is similar to the effect where, by raising your heart rate through exercise, you tend to reduce your average heart rate throughout the whole day).
I'm also concerned about the missing external costs. The infrastructure required by cars is considerably more time and labour intensive than that required by bikes. If the roads are designed purely for bikes, then we wouldn't need traffic lights running all day long or speed cameras. Also repair costs would be less, but that's probably not too relevant is it's only really the heavy vehicles (buses, trucks) that cause significant damage to the roads.
I wonder what the CO2 comparison would look like if they factored in the extra health care required for the burger munching motons?
The study looks at vegan diets (lowest carbon) , paleo diets (highest carbon) and a typical American diet.
You can roughly guesstimate where your own footprint lies.
Fine, except that the research then uses those extra calories required as a straightforward measure of extra calories consumed, from which it then extrapolates CO2 emissions. But calories required is a problematic way of measuring calories consumed in this scenario, because it assumes that the drivers and cyclists are consuming calories directly proportionate to their energy needs. But in practice we know that - in the West at least - large numbers of people consume more calories than they actually need to meet their energy requirements; this is the reason we have such high levels of obesity. Without taking into account how much of the additional energy requirements of cycling are already mirrored by the excess calorie consumption of the average driver, the applicability of these findings to real world scenarios is highly problematic.
To give a real-world example; when I shifted from driving to cycling to work, I was already recording my calorie intake. My calorie consumption did not increase to meet the additional energy requirements of cycling, because the excess calories I was already eating were sufficient to cover that. All that happened was that I burnt more of those calories off and slowly lost weight over a 6 month period until I reached a new equilibrium. This is just one example, not intended to refute the findings of this research, but rather to point out the limitation of basing measures of energy consumption on measures of energy requirements.
Of course, this limitation of the research is obvious from reading it. But let's be honest, the methodological limitations are not what is going to be focused on, only the headline message that 'cycling emits more CO2 than driving'. It would have been nice if the author could have drawn more attention to the limited real-world applicability of his findings in the accompanying commentary.
Bingo.
The major fallacy, is the idea that cycling would lead to a 1:1 increase in calories consumed to match energy expended. America (this being a US report) has a huge surplus of dietary energy, and our increasing sedentary lifestyle is a major public health problem.
Well, that and the specific calculations and focus on Paleo diets is rather odd (and markedly out of line with existing research).
Exactly: he was chasing a headline/abstract and came up with research to fit it.
Great point. And one born out by own measurements.
I rather suspect that the author does not particularly care about the impact on cycling. My suspicion is that this is part of the current wave of vegan propaganda.
Nothing wrong with a vegan diet. The problem comes if this tosh is picked up by MSM, and spun as 'see, cycling's no better than driving'.
I never made any judgement on the "wrongness" or otherwise of vegan diets. Merely speculated that the reason we're seeing this is as part of the uptick of promotion of veganism that seems to have been doing the rounds lately.
A major assumption being that car drivers don't eat...
Can't wait to see what facts the Daily Mail can get from this bullshit.
The French and Jeremy Corbyn ride bikes, pollute the planet so we have to leave the EU.
[[[[[ If 3 cyclists eat 3 cans of beans in 3 minutes and then ride a 50-mile T.T., surely their emissions will guarantee a 3-minute beating of their (3) PB's? Off-message, I know, but I'm fartoo confused by El Willio to concentrate...
Unless he can show that cyclists eat more meat tHan drivers this is questionable in the extreme.
Also most people are not on the paleo diet, and most cars are not a prius.
Pretty sure my meat consumption hasn't gone up since starting cycling, sugar yes, meat no.
Agreed. What sort of Venn diagram would you end up with?
If the researcher is going to use this kind of argument, then I'd have thought those that expend calories in a gym without gaining a yard in transportation would be a worse 'culprit' than a cyclist (only by using his logic and not any I subscribe to, in the world of the sane). Surely combining your exercise with transportation is the perfect, most efficient combination possible?
Please show a little sympathy for Mr Thorpe. I strongly suspect that he has to create some original research to progress academically and he has demonstrated some imagination in sweating his sources (tiny data sets etc) to reach this conclusion.
It is not pretty, but it is the reality of academic life in the twenty first century. Simply regurgitating the known health, financial, social benefits etc of cycling will not pass muster.
"Specifically, graduate student Daniel Thorpe singled out cyclists who follow the Paleo Diet"
I think you'll find more car drivers on the Paleo diet...
At first, as pointed out above, I believed that a school-boy error had been committed: not considering how many gCO2e the occupants produced per kilometre.
Let us assume that the car driver averages 60 km/h (37.5 mph), which is in-the-middle compared to other choices for simple "back-of the-fag-packet calculation": 30 km/h or 90 km/h. 30 km/h, which will double the following result. 90 km/h (56 mph) will reduce it by a third. The choice of speed isn't that important.
Allow our average American to consume their 2600 kcal/day, which works out at 108 kcal/hr. At the 60 km/h the occupant will produce 1.8 gCO2e/km, which is fairly insignificant compared to the CO2e from the car. I think that is why the CO2 produced by the occupants is not included, regardless of their vegan or other credentials. I was rather hoping to be able to prove a point.
I do have a concern, which is how the figure of 50 kcal.km was obtained. A cursory search led to a calculator http://www.tribology-abc.com/calculators/cycling.htm. Thanks for tribology for that. I am sure that, as the Beeb would say, other cycling calculators are available. A quick play with play with their default values gave a figure somewhat less than in the article, but I am sure within a suitable range depending on a cyclist's weight, efficiency etc.
The next part of the article is rather confusing - referring to land use. The person, whether driver, cyclist or both (though not at the same time
both eat - I assume. Both make use of the petro-chemical industry - one rather more than the other. However, that does neatly bring us back to J Harrison, for the second statement is not without merit as a car.
It's a few years' old, but I've quoted scientific papers older than that; this article in The Guardian (https://www.theguardian.com/environment/green-living-blog/2010/sep/23/ca...) gives that half of a car's emissions occur during manufacture. I must admit that I only skimmed the article, as I have to go to work tomorrow. However, if that is for an average car, the figures per km for a car are out by a factor of 100% and those of the Prius would therefor be more inacurrate. No figures are available per kilometre for the manufature of a bicycle, but they are more simple machines.
This would give 600 gCO2e/km to the average car, 450 gCO2e/km to the Prius. Compared to roughly 200 gCO2e/km to the meat-munching Paleo cyclist, through to about 150 gCO2e/km for the average American cyclist and 100 gCO2e/km to the vegan cyclist. So it seems to be several times worse to drive than cycle.
As the author pointed out - cars allow one to travel many more miles, so in using one one tends to have a higher gCO2e footprint.
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