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You are what you eat ... and drive or ride, says climate change scientist

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.” 

Born in Scotland, Simon moved to London aged seven and now lives in the Oxfordshire Cotswolds with his miniature schnauzer, Elodie. He fell in love with cycling one Saturday morning in 1994 while living in Italy when Milan-San Remo went past his front door. A daily cycle commuter in London back before riding to work started to boom, he's been news editor at road.cc since 2009. Handily for work, he speaks French and Italian. He doesn't get to ride his Colnago as often as he'd like, and freely admits he's much more adept at cooking than fettling with bikes.

102 comments

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Jharrison5 [141 posts] 1 year ago
22 likes

A Prius may emit 150 gCO2e/km. It's occupants have emissions too, even at rest.

Is the chemical and material cost of manufacture neglected in these calculations?

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oldstrath [924 posts] 1 year ago
11 likes
Jharrison5 wrote:

A Prius may emit 150 gCO2e/km. It's occupants have emissions too, even at rest. Is the chemical and material cost of manufacture neglected in these calculations?

 

And apparently the car driver doesn't take aerobic exercise. This really is an incredibly simplistic bit of arithmetic.

 

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HarrogateSpa [500 posts] 1 year ago
26 likes

If you have to attribute a funny diet to 'cyclists', it's probably a sign that the research is total bollocks.

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ragtag [219 posts] 1 year ago
14 likes

And apparently drivers do not eat either. Americans consumer 122 kgs of meat a year, reckon a fair few of those are at drive thru McDs.

Compare the bike to the car.. or the driver to the cyclist. Not the banana to the apple. If he wants to compare the fuels then he needs to look at the entire supply chain for fuel (research, discover, drilling, transportation, processing) not just the cost at the point at which it is burnt. 

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Leviathan [2868 posts] 1 year ago
8 likes

Great work from the Ed Koch school of Environmental Sciences. But I believe that Chocolate, cake, coffee and crisps are all vegetable based products. Or is a Greggs Steak bake paleo?

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handlebarcam [1064 posts] 1 year ago
3 likes

I knew one day it would be proved that Alberto Contador was responsible for destroying the planet.

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tritecommentbot [2268 posts] 1 year ago
16 likes

Because people only eat their required energy expenditure..

 

Who funds this shite. Some right-wing nutjob lobby no doubt.

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Hipshot [61 posts] 1 year ago
17 likes

Specifically, graduate student Daniel Thorpe singled out cyclists who follow the Paleo Diet.

Presumably this also applies to pedestrians who follow the paleo diet.

So this has nothing to do with cycling, it's to do with diet! 

 

 

 

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oldstrath [924 posts] 1 year ago
5 likes
unconstituted wrote:

Because people only eat their required energy expenditure..

 

Who funds this shite. Some right-wing nutjob lobby no doubt.

 

Sadly, the funding seems to come from respectable sources. He seems to have cooked up this simplistic twaddle all by himself, without any prompting.

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ragtag [219 posts] 1 year ago
4 likes

Wasn't there that other idiot that said something about cyclists breathing more? Is this the son?

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bikebot [2119 posts] 1 year ago
6 likes

And soon to appear on the Ig Nobel nominations.

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barbarus [502 posts] 1 year ago
7 likes

This would all make perfect sense if all those car drivers were vegetarians who never travel by aeroplane, used air conditioning etc

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oldstrath [924 posts] 1 year ago
12 likes
L.Willo wrote:

Really interesting research. It just goes to show that environmental problems are wicked and there rarely are simple solutions.

I have just enrolled on the online course: https://www.edx.org/course/energy-within-environmental-constraints-harva...

to learn more and discuss the details with the authors.

I do hope some of you thicky bricky, back of a fag packet, stick a thumb in the air researchers with your oh so superior Diplomas from the University of Life will be enrolling to show these Harvard Professors and Research Fellows their schoolboy errors ....  24

 

 

Oh god. OK, bit of real world arithmetic for you. I cycle 12 miles each way, so roughly an hour of aerobic exercise. I emit whatever CO2 equivalent. Now imagine my colleague who drives, maybe in a Prius, the same distance. IF I were eating a paleo diet and he were a vegan, maybe my CO2 equivalents would be similar to his. Very nice.

But this 'analysis' omits the CO2 costs of construction, it omits the CO2 emissions my colleague makes while sat in his Prius, and omits the CO2 emissions he makes while taking the aerobic exercise I have already taken. More generally, as even the researcher admits in his discussion, he ignores the fact that car driving allows much longer travel distances, and requires an energy-expensive road building and maintenance programme.

So yes, environmental problems are indeed 'wicked', and this simplistic comparison of the most damaging cyclist, with the most virtuous Prius driver (who takes no exercise and eats no excess food), really doesn't help.

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Carton [393 posts] 1 year ago
13 likes

"Assumptions are dangerous things to make, and like all dangerous things to make -- bombs, for instance, or strawberry shortcake -- if you make even the tiniest mistake you can find yourself in terrible trouble." - Lemony Snicket

He's underestimating the fuel efficiency of your average commute (25mpg, for rush hour in the US), overestimating the energy demands of cycling (apparently, I'll expend 5,000 calories in order to complete my next metric century - at commuting pace, no less - I'll keep my fingers crossed), discounting the idle energy expenditure of your average driver (the average US male weighs 200 pounds, and contrary to popular opinion they don't produce their own energy) and, (at least admittedly) not taking into account that people who use their bike will end up travelling less (I know someone in the US who had a 200 mile roundtrip commute, that's going to be quite hard to do on a bike). When you combine all that, it gets really fun. Someone who trades his car in for his bike and starts commuting 20 miles (average US commute) to work is going to get fairly fit compared to someone who just drives in. He's certainly going to get much more efficient than 50 cal/km cycling. Also, the bike-commuter is on average going to end up losing weight (as per previous studies), which means that not only is his additional intake going to be less than the estimate, but his maintenance intake is going to be less, while average Americans are going in the opposite direction. Which means that even discounting for idle expenditures, the exercise will likely significantly overestimate the caloric intake difference. 

Also, if you're going to include second order effects like land usage, not only is the cyclist more likely to relocate closer to work, but also somewhere where other things are close by. So he's going to make his whole life more efficient. And as more people do the same, transportation energy expenditure would going to go down significantly. Add that to other second-order effects not being taken into account, including infrastructure maintenance and congestion. 

I think it's good to discuss these notions, even when they're not fully thought out, but it gets dicey if/when more mainstream outlets start picking it up without understanding that it's not a proper study.

 

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CarlosFerreiro [121 posts] 1 year ago
0 likes

It'd probably be more helpful to compare the effects of different transport modes across existing populations than go all the way down to an individual on an specific diet? 
E.G. If Los Angeles cycling modal share replaced car use for 10/20/30/40% of in-city journies, what would the effects on emmisions, polution, conjestion, short and long term health etc.
One on one only tells you much at the extreme, where it's the average you want to know about for any policy choices?

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davel [2005 posts] 1 year ago
0 likes
L.Willo wrote:

Really interesting research. It just goes to show that environmental problems are wicked and there rarely are simple solutions.

I have just enrolled on the online course: https://www.edx.org/course/energy-within-environmental-constraints-harva...

to learn more and discuss the details with the authors.

I do hope some of you thicky bricky, back of a fag packet, stick a thumb in the air researchers with your oh so superior Diplomas from the University of Life will be enrolling to show these Harvard Professors and Research Fellows their schoolboy errors ....  24

 

 

I'm sure you appreciated his simplistic assumptions.

Don't forget to ask him to factor in the impact of cyclists deferring to every other category of road user at each interaction, and to clarify which segment all your emissions should be grouped under.

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BBB [461 posts] 1 year ago
8 likes

His research makes as much sense as Paleo diet itself.

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efail [109 posts] 1 year ago
2 likes

This 'Paleo' bloke, is he a cyclist?

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handlebarcam [1064 posts] 1 year ago
5 likes
L.Willo wrote:

I have just enrolled on the online course: https://www.edx.org/course/energy-within-environmental-constraints-harva...

Were you able to transfer credits from your previous studies?

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Hug [12 posts] 1 year ago
4 likes

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  21  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.

Jharrison5 wrote:

Is the chemical and material cost of manufacture neglected in these calculations?

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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Jharrison5 [141 posts] 1 year ago
1 like

"Specifically, graduate student Daniel Thorpe singled out cyclists who follow the Paleo Diet"

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Leviathan [2868 posts] 1 year ago
13 likes
L.Willo and Ronnie Corbett wrote:

I know my place.

I look down upon you.

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vonhelmet [847 posts] 1 year ago
12 likes
L.Willo wrote:

I would not have the audacity to question someone so learned in his field without equivalent credentials. I know my place.

I do however look forward to observing the debates in the forum where you lot take these two Harvard / MIT educated shysters to task with your rules of thumb, back of a fag packet calculations and combined double digit IQ.  24

What are you on about? No one is disputing the "findings", only pointing out that they are so narrowly drawn as to be basically meaningless. It's like pointing at the ThrustSSC and saying "Some cars use more fuel than a Boeing 747."

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Bill H [60 posts] 1 year ago
5 likes

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.

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barbarus [502 posts] 1 year ago
4 likes
L.Willo wrote:

I know my place.

Sadly not true

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brooksby [2711 posts] 1 year ago
3 likes
HarrogateSpa wrote:

If you have to attribute a funny diet to 'cyclists', it's probably a sign that the research is total bollocks.

Exactly. WTF is the Paleo Diet anyway? I've never heard of it.

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wycombewheeler [1237 posts] 1 year ago
4 likes

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.

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wycombewheeler [1237 posts] 1 year ago
0 likes
Leviathan wrote:
L.Willo and Ronnie Corbett wrote:

I know my place.

I look down upon you.

Only as you are crossing a bridge?

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PhilRuss [395 posts] 1 year ago
1 like

[[[[[  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...

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tonyleatham [53 posts] 1 year ago
0 likes
unconstituted wrote:

Who funds this shite. Some right-wing nutjob lobby no doubt.

Much more likely to be a left wing nut job

 

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