This graphic claims to show greenhouse gas emissions saved by riding a bicycle. But this infographic is definitely overstating the actual savings.
At face value, this graphic claims that 216 grams of greenhouse gases (assume CO2) are saved for every kilometre travelled by bicycle. The big problem here is that bicycling doesn’t actually remove any CO2 from the atmosphere; it only produces savings when it displaces a different activity that would have emit even more. The other activity is called the baseline, and what we pick for the baseline has a huge impact on savings calculations.
Imagine that this person was previously driving a gasoline-powered car to work, every day, alone. That is our baseline, and the baseline represents the highest possible savings. We might save 5% by changing our driving style, or 50% by switching to a different mode of transportation, or 100% by avoiding the travel entirely. But we can’t save more than 100% (at least without some technology to capture carbon from the atmosphere).
A gasoline powered car emits, on average (median) between 121 and 150 grams of CO2 per km of travel. But the graphic is claming that the cyclist is saving 216 gCO2/km, which would be savings of 144% or more! That’s nearly impossible! It could only make sense if the car in the baseline something is a very high-polluting car like a Porsche Panamera Turbo, which seems pretty unlikely.
But even the assumption that every bike ride displaces a trip by car is pretty ridiculous, because in the city that produced this infographic only half of all trips are by vehicle. The rest are a combination of walking, bicycling, bus, and train. Travel by public transit emits about 50 gCO2/km on average, or even less if travelling by electric commuter train. And an electric car emits 0 gCO2/km travelled.
The infographic claims that travelling 306 kilometres by bicycle savings 66 kg GHG, but the real savings are probably somewhere in the range of 15 - 45 kg depending on the baseline mode of transport.
If you are responsible for calculating reductions of greenhouse gas emissions, or if you’re building tools that help to produce these estimates, you must factor in baseline emissions otherwise the estimate is worthless.
This post only discusses tailpipe emissions – the kind produced locally while the action is taking place. It’s also worth thinking about lifecycle analysis, which greatly expands the scope of measurement to include emissions produced in the manufacture of gasoline and motor vehicles, and other input energies. But that’s a topic for another post.