In my (almost) three decades, I've visited most of Europe, had several jobs in several countries and lived in four different homes. The only time I was ever on an aeroplane was when I was 3 years old and my parents took me on a trip to Spain. I've never owned a car (and if I ever do it'll be a zero emission recycled beast). I've always traveled by train or coach. I use my very own two feet and public transport to do most of my commuting. Every once in a while I need some sort of vehicle to move large items from A to B - when this happens, I take a taxi. When I accept a ride from A to B, I only to do this if the driver doesn't have to go out of their way for me.

Seriously folks, it's not that hard. I've never known it any other way.

I think the data on the bike is inaccurate. There is CO2 being discharged. It takes food and energy to power the leg muscles and therefore a value of 0 is not possible.

Actually the per-passenger-km requires an assumption on the yield of each form of travel (number of people/number of seats) Airlines often have yields in excess of 80%, while most cars often only carry one person, so the true emissions are 4x those listed.

In any case the average airline with 80% yield gets between 46-55 mpg per seat.

Also, rail travel requires compensation for yields, increased distances due to indirect routes, speed (higher speeds = more emissions) and form of energy used (ie in France electrified trains are ultra-low emissions due to relying on nuclear power).

So basically, the true answer to emissions by type of transport are far more complicated than that chart lets on.

Still, I see air travel as being something that outweighs the negatives of it's emissions for travel in excess of 800 miles or so.

Shouldn't the bicycle in that graphic have a non-zero value?

A bicycle is only capable of covering distance with a rider providing power, and that rider is exhaling CO2 as part of the aerobic process of powering the bike. That CO2 the rider is exhaling is expensive, too - it's at the end of a long chain of food-production and transportation carbon costs. Maybe it's a small quantity and it falls off the graphics two significant digits?

Anybody know what the net carbon-dioxide production is for a person pedalling a bike a kilometre under average road conditions?

Still, without accounting for the rider's carbon footprint, the bike may as well be a kitchen table - they produce 0 kg CO2 / km, too.

Just with that diagram, all that might be at the tail pipe, but seriously - people eat food for energy. and food is CO2 intensive.

unless your eating only organic food from your backyard, a bicycle is not indirectly 0. which since the train is rated indirectly as it has no tail pipe on it, i think its very fair to say that this diagram is WRONG.

id love to know what it really works out to, tho id still believe the bicycle would be on the bottom.

ironically tho the picture has nothing to do with the article.

If the cyclist is vegetarian then he/she is carbon neutral, releasing back only sequestered CO2. It is only CO2 positive if the cyclist eats meat.

As I've noted here before, land transport, especially rail, is not correctly measured if you ignore the carbon cost of road and rail construction, as well as the carbon cost of cars, which are replaced far more often than trains or airplanes.

Consider that a 100 km stretch of railway requires some 250,000 tons of steel and concrete just for the rails and ties. To that, depending on the route, you can add civil works of all kinds (bridges, tunnels), earth movement, and plenty of local environmental disruption.

So rail has to offset a heavy CO2 burden, and it can't do it in long and thin routes. It can in short, dense routes, such as in Europe and the US Northeast or California. Unlike air, rail's CO2 efficiency is a function of the density of the route. Something similar happens to cars.

A "one size fits all", rail is always better attitude is just not a reflection of the facts. Air travel is CO2 efficient over long distances. The problem with air travel is not that it is particularly polluting per passenger mile if full life cycle CO2 footprint is considered. The problem is that it makes tremendously long distance travel too easy, and thus encourages it.

Ah, the lessons of 9th grade math...

The diagrams shows the cyclist emitting "0 kg" CO2. Not to two decimal places like every over value, but just 0. If you are rounding to the nearest whole number, a cyclist could be outputting 0.49kg CO2 and the value as labeled in the diagram would still be correct. This is why many food packages say "0 Trans Fats" instead of "No Trans Fats", because it's just rounding, and they actually may contain high amounts.

As to the claim Vegetarians emit ZERO CO2, that's also pretty silly. Do vegetables magically fly from the farm to the store, or perhaps are they also carried by truck? Yes, raising animals for food has a high CO2 footprint, but just because you don't eat meat doesn't mean ALL contributions go away. Unless you grow all your own food on-site.

As for the text of the post, one point on there-- who the heck drives 48,000km in a year?? That's twice the average that is used to calculate leases and warranties on cars, and aside from those with 50km/day commutes, even 24,000kms a year is pretty crazily high (65km a day!?)

Throw a real number on the graphic then we'll all be happy :-)

So electric cars get called green with barely a peep, then people quibble over CO2 emissions from a cyclist. I'm almost speechless. Almost.

A person needs 30 minutes to an hour of exercise a day to stay healthy so, unless the person is cycling a lot, their CO2 emissions from cycling won't increase overall emissions. As well, by keeping ones weight down by cycling, less energy will be consumed when a person is in a car or in a plane or in an elevator. Anyway you slice it, cycling does really not contribute to CO2 emissions. Get real people.

The human body is far more inefficient at converting fuel (food) into mechanical energy than a modern internal combustion engine. I've read that modern IC engines on passenger vehicles are around 20% efficient, and a higly fit cyclist is something like 6%-8% efficient.

Also, the petroleum fuel delivery infrastructure is much simpler and more efficient than that for human food. Petroleum is comparatively easy to refine, transported, and sold in bulk.

Human food, on the other hand, needs to be planted, cultivated, harvested, refined in various ways, packaged, preserved, refrigerated, transported, and sold through retail outlets. Then it must usually be prepared by cooking. It often has a limited shelf life, and then the effluent must be disposed of and treated. And then you still have to do the dishes. That all takes lots of energy, which produces CO2, vegetarian or not.

By comparison, driving a Cadillac El Dorado starts to look pretty efficient.

Why would anyone waste food to run a bicycle? Cars and trucks were invented for good reasons.

To be fair, if you want to add the carbon cost of food production to the footprint of the bike then you have to add the carbon cost of producing the fuel that you are burning in planes, trains and automobiles (not just the efficiency of consumption).

It also gets complicated to consider the CO2 output of the rider due to riding because humans output CO2 by existing. It is not impossible it is just tricky.

I guess the upside here is that people are trying to evaluate relative efficiencies and impacts, and inspecting the data, rather than simply accepting received wisdom.

It's clear that pedaling a bicycle will result in more C)2 being generated, than if that person was sitting still - so that is a net positive emission.

Lloyd's rejoinder "If the cyclist is vegetarian then he/she is carbon neutral, releasing back only sequestered CO2. It is only CO2 positive if the cyclist eats meat." is a jovial nudge, I hope.

If the airplane is biofueled from soybeans will it also be climate neutral? Should I then use my soybean fueled helicopter to go down to the corner market to pick up a quart of milk? Lloyd has expanded the scope beyond the study. Combustion of a fuel for motive power creates C02 emissions, plain and simple. It is useful to evaluate which are more substantial and to make decisions based upon that.

Where the fuel comes from and how it is produced is another series of questions with their own merits.

I suppose oil is very simple and highly efficient - when you don't consider the eons of tropical forest, bogs and dinosaurs that had to live and die and be compressed to form it over millions of years. Just like we appreciate other areas of the extractive economy that relied on biological and geological processes to produce.

Done right, food production is indefinitely sustainable - something that oil production will never be. Bicycle propulsion has long been recognized as the single most efficient form of locomotion - better that a full airplane, better than walking, better than everything else in between, with the possible exception of a sailboat.

If you look at the whole supply chain, no cycling is not zero, however, to suggest it's inefficient to the extent that a Cadillac becomes comparable is absolutely absurd. I realize it's an exaggeration, but still..

If you are going to get that not picky into the marginal co2 output of cycling for transit, by factoring extra food and breathing, then lets pull out other variable as well and start nit picking private automobile transit.

How about the waste of cars idling in traffic, burning fuel without acomplishing distance. A cyclist, by virtue of being narrow and able to cut through congested traffic is almost always making forward progress.

Cyclists also typically behave more efficiently, which is intuitive when you are your own motor. For example, many drivers continue to accelerate until they are forced to stop, this is wasteful fuel economy. Most cyclists will try to time lights by slowing down in advance when it is red so as to avoid complete stops and not waste forward momentum.

CO2 is emitted in the substantial under taking of constructing and up keeping roads. Damage to roads becomes proportionally greater with the weight of the vehicle. Thus more cyclists and less cars, suv's and trucks, would mean roads would last significantly longer.

Most of the energy cars burn is spent carry the weight of it self, where the inverse is true of bikes which are lighter than the person they carry.

CO2 is emitted in the supply chain of producing any product, but a bicycle, with it's small light weight tubing and simpler components, requires far fewer resources to construct. Light weight and compact space makes it possible to ship bikes in mass more easily to shops by comparison to shipping cars to dealerships.

Parking spaces are a significant issue in any major city. Enormous amounts of land are wasted on expansive parking lots. Numerous bikes can fit into the space of a single car. Parking garages take up less land space, but require significant costs and resources in construction and upkeep, and generate slowed often idling traffic, and extra co2 emitted as the cars have to burn extra fuel winding up and down ramps.

To answer the question earlier:
"Why would anyone waste food to run a bicycle? Cars and trucks were invented for good reasons."

1) More efficient for reasons above, thus not a waste.
2) I hate looking for parking.
3) I genuinely enjoy the act of riding and find my self feeling better both physically and mentally.
4) I've met tons of amazing people and made lasting social connections through cycling. You don't meet people sitting in your car.

I think that bicycling uses less oil than riding in a car no matter how you look at it. Michael Pollan's book cites a figure of a 10 calories of fossil fuel energy : 1 calory food energy for fast food. Let's say you are already "greening" (or else why are you reading this blog?) and you manage to reduce that to 8 calories of fossil fuel energy : 1 calorie food energy. Cycling requires about 120 kJ of food energy per mile , so let's convert that to 960 kJ per mile. This converts to 81 mpg per person. Since most people drive alone to most places in cars that get FAR less than 81 mpg, therefore for most people cycling is the better option, AS LONG as you change your diet to make it more green.

Something I find interesting in this debate here is that all of you seem to assume that cyclists eat more food/calories than drivers. I have never done any research into this, but I suspect that people who drive eat just as much food as cyclists & that's why 'chronic drivers' tend to be overweight... If I'm right, then cyclists would work out to be carbon neutral, as compared to drivers.

So the people in the plane, car and train have not been eating, or breathing then? That's just something us cyclists do??! LOL

I think a proper design with education can change people's use and interaction with architecture. I am a big fan of the latest sustainable practices in the residential construction business and there are a number of examples of successfully marrying sustainable practices with practicality and client requirements, reducing the need for energy consumption significantly. I personally am excited about the Sustainable House I saw on the Science Channel that gets the house to be "energy-free"., reducing the need to local utility energy.

Check it out here