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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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111 comments
Were you able to transfer credits from your previous studies?
I could be arguing in my spare time......!
El Dildo,
As a fully graduated and qualified researcher, with 17 years real life experience in the field, I feel qualified to question their methodology and the interpretation of the findings. Fortunately, the "thicky bricky" people of the forum have shown either a superior level of intelligence than you credit them with, or the research is indeed very flawed.
The data may actually be really interesting and provide some really interesting points, when you consider shared journeys things can quickly start to look different (so long as there's no de-tour for the sharing). Maybe it suggests that if you could get 20, 30 or even 40 people onto a mode of transport, with a pre-determined route, all sharing the cost, we may have hit gold. I'm not sure what this idea could be, I've reacked my brain but it's like waiting for a bus.
The main flaws are the paramters and comparisons used and extrapolating things from a tiny sub sample of the population which has lead to a conclusion that "some cyclists may actually be more harmful to for the environment than some cars" as the lead in the piece allowing those that are deliberately feckless to ignore the standard. I can find a mass murderer that has contributed a greater imapct on reducing carbon emissions than a tree hugger, it doesn't make murder the preferred approach.
Wasn't there that other idiot that said something about cyclists breathing more? Is this the son?
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!
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.
Much more likely to be a left wing nut job
Really, how do you work that out?
Climate change is DEFINITELY a poster child of the left. I can't see any right wing organisation funding any kind of research into climate change, even if the intended outcome is to demonstrate that cars are more virtuous than bikes. They're much more likely to want to disparage the entire notion of AGW.
Yeah I guess.
If you've been living under a rock and missed the constant right wing lobby funded research papers that have been in the press constantly for years on end.
Be serious.
I knew one day it would be proved that Alberto Contador was responsible for destroying the planet.
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?
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.
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.
In four words "eat like a caveman".
It's the latest fad diet with a long list of rules, when most of the problem is simply that we've normalised heavily processed foods high in carbohydrates.
Where have you been? Living in a cave....? Oh, hang on...
What about all those motorists who drive in for a Big Mac or KFC ? Millions of em in USA alone ! Their meaty diet plus co2 emissions make this survey mighty suspect !
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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