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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
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.
I look down upon you.
Only as you are crossing a bridge?
Doesn't everyone?
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."
Sadly not true
I can't decide if L.Willo is being sarcastic or not. Poe's Law (https://en.wikipedia.org/wiki/Poe%27s_law) strikes again.
Anyhow, that quote up there is a lovely example of argument from authority (a common logical fallacy): https://en.wikipedia.org/wiki/Argument_from_authority
Huh? If I've read this right, he's a grad-student, not a tenured professor. Even I've been a grad-student, as have huge numbers of people. I've known lots of grad students (including in this very field), they are ten-a-penny, particularly in the US as the US system very much depends on their cheap labour.
And the article was on a blog, not a peer-reviewed journal, so anyone can question it, no 'credentials' required. You need to get over your fawning towards the 'Harvard educated', (my Yale-educated friend would beg to differ on that one!).
if it isn't in a reputable peer-reviewed journal it's probably not intended to be taken entirely seriously.
Sounds like a, as you put it, 'back of a fag packet calculation', made for fun and publicity, given the weird assumptions about diet and calorie expenditures (how many cyclists follow 'paleo diets'? like 0.01% of them?) - though it might be partly about drawing attention to the valid point that meat-production is a significant producer of greenhouse gases.
You missed the point that the research was backed and assisted by Professor David Keith and published on the latter's blog. You also missed the point that both are teaching on the edX course referenced in the article.
I can guess your next question, who is this Professor David Keith environment hater with no more credibility than your average below the line road.cc poster?
Well see for yourself:
http://static1.squarespace.com/static/5264256ae4b0b34efecab6b7/t/56faa8e...
... and I would invite any of the "he doesn't know what he is talking about!" brigade to post your own credentials so we all can see exactly what you have contributed to furthering environmental science.
I won't be holding my breath .....
Congratulations on missing the point quite so well. Actually quite a few points. Ranging from the relatively trivial (the numbers are weird, they really are, go look at a sports science text or your own Garmin after a ride) through your authority worship (crap science there!) through to the weirdness of the comparison between a meat munching cyclist and a vegetable eating Prius driver.
But the biggest issue you miss is that this work is so narrowly focussed on one consequence of exercise that it has the potential to be seriously misused by car salesmen and evangelists. As I and others have tried to explain, even if all the numbers were believable, they ignore completely the other consequences of shifting from cycling/walking to car driving.
In summary, I don't doubt Dr Keith's credentials as a climate engineer. I do, however, believe that his specialised knowledge has led him to ignore important consequences of his work.
So your attitude is don't publish the outcome of research in case other people misuse it? Nothing would ever be published in that case.
By all means constructively criticise those who misunderstand, misinterpret or attempt to misuse information.
What is however completely intolerable are the posters who are not fit to lace the authors' shoes denigrating them personally, their motives and their work because they do not like the outcome. One barely sentient clown has actually sent an abusive and offensive email if he/she is to be believed. The chutzpah!
But censorship? No. Attack the messenger? No.
Uncomfortable truths are better than obfuscation and downright lies.
Where to begin?
Firstly, you're constructing a straw-man argument (https://en.wikipedia.org/wiki/Straw_man) as you're mis-representing Fluffy's position. He never said about non-publication of research - suspect he probably thinks that dodgy research should be pointed out and not celebrated.
Secondly, you seem obsessed with researchers' reputations and not focussing on the actual research. It's largely irrelevant who performs experiments as long as valid methodology is used. This particular research has very questionable choice of data sets to focus on and we should recognise that and point it out. To think that because someone is a professor that they are infallible is not a particularly effective way of evaluating research.
I don't know what kind of personal attacks have been made and I agree that attacking research simply because you don't like the outcome is wrong. However, I don't think that is happening here. From what I've read, it sounds more like criticism (not all constructive).
I also think uncomfortable truths should be preferred to obfuscation, but this research looks more like using cherry-picked numbers to hide what typically happens with CO2 and modes of transport. It seems to me that he was using the outliers (i.e. Prius and paleo-diet) to make a point and that is more politics than science.
No, my attitude is that people should care about accuracy, should do work which covers all the system, not just a tiny bit, and should think hard about the consequences of their work.
I'll accept that the last of these can look a bit like self censorship, but 35 years of working in medicine probably also induces specialist disease, and there is no way I could let this dubious work, with its scary implications if used thoughtlessly, go unchallenged.
And yes, I've also written to Professor Keith, pointing out the because,nd my concerns. From my academic address, because alas, excessive respect for titles is not confined to L Willo.
This is so naive. You clearly know little about how academia works, and particularly how it has changed over recent decades.
As it happens I don't think this single post on a blog is really an example, but there _is_ a problem with an ever-increasing pressure to publish-or-be-fired - and there does seem to be an ever-increasing tendency of university press-departments to misrepresent research in order to gain the attention of the media. And sometimes this even seems to creep back up the chain to affect what gets into papers themselves.
But putting tenuous work on the web is fine, what isn't so fine is when people like you misinterpret it and fail to look at what it actually consists of, in favour of just looking for conclusions you like.
It says something that you presume something to be an 'uncomfortable truth' even when it hasn't been established to be 'true' by the normal process of peer-review. Which does exist for a reason you know? Otherwise we could just let anyone with credentials Willo finds impressive publish anything they want on the web and take it as being necessarily 'true'. Would make 'science' much cheaper and easier, that's for sure, could do away with the whole business of journals and peer-review and replication.
Actually, given your utter nonsense about 'personal attacks' on the authors and the idea that its inherently wrong for an academic to disagree with another, I really should accept you are just a classic-troll and stop bothering.
Can we _please_ have a kill-file/ignore-list facility on here?
From the man who won't even tell us where he received his cycle training.
Oh go on.
Oh for God's sake! Its the work of a grad-student. And you acknowledge this is something on a BLOG, not a peer-reviewed journal. People can put almost anything on blogs. If he wants the argument to be taken seriously he needs to publish it in a proper journal, otherwise it's just something someone wrote on the internet.
Furthermore it says what it says, not what you want it to say. You don't have a publication history as far as I am aware, so people are free to disagree with your misinterpretation of the blog.
Have you ever heard of the fallacy of 'argument from authority'? Your fawning over someone's credentials and desperate attaching yourself to the coat-tails of someone who you think has better credentials than you is a bit embarrassing (some of my friends are fully-tenured professors, doesn't stop them constantly being wrong about things! ).
Its really not complicated - just because the conclusion fits your car-worshipping agenda doesn't make the argument sound, not until its gone through the proper scientific process of peer-review. But, as I said, I am sure there is a valid point in there about the environmental-impact of meat-production and consumption.
"some of my friends are fully-tenured professors, doesn't stop them constantly being wrong about things! "
Guilty!
This 'Paleo' bloke, is he a cyclist?
His research makes as much sense as Paleo diet itself.
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?
"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.
What is more interesting to me is how this research affects my attitude to sport. Clearly the Tour de France is a pointless Greenhouse Gases catastrophe when you consider all of the extra meat and dairy sourced calories consumed in training and in the race to allow the athletes to perform? Would it look so benign if that was a huge convoy of Ford Focuses driving 150Km every day for no purpose whatsoever? How many TdF stages equals one Formula one race or is that question the wrong way around? Hopefully by the end of the course I will learn how to make those calculations.
What about Ride London and the London Marathon? I have completed both and now feel quite ashamed when I consider the totally unnecessary calories I consumed in training as well as during the events, the concommitant increase in greenhouse gases and land usage.
Can you claim to care about sustainability and NOT be a vegan?
Lots of food for thought ...ahem. That is what good quality research should provoke .... in the open-minded that is ..........
New research suggests commenting on road.cc is extremely calorie intensive. For the sake of the planet, you should cut back.
.... temporarily deactivate ignore filter .....
Says the spambot who has made 1853 poor quality 'posts' ....
.... reactivate filter
Ever going to answer the question on who provided your training?
Or will you run away again?
This would all make perfect sense if all those car drivers were vegetarians who never travel by aeroplane, used air conditioning etc
And soon to appear on the Ig Nobel nominations.
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 ....
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.
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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