This is perhaps a surprising question to ask. The assumption we’d all probably make is that bikes must be the greenest form of transport. Certainly that’s a view put to me in recent comments, arguing that I shouldn’t be promoting wind powered cars – mainly because bikes are greener than any kind of car.
But it occurred to me – there’s an assumption frequently made that riding a bike is for free. And it’s not. You have to power the bike, it’s human power but that’s not free – we need food to do work.
The rates at which we burn calories and therefore food are pretty well established for various activities – resting, walking, running for example – as are the carbon impacts of food and therefore of the calories we use.
Typical daily calorie requirements are also well established. And if you up your activity level you up your need to eat – it’s that simple.
Easy enough then to take a closer look at just how many more calories it takes to ride a bike, and what additional carbon impact comes from that – compared to the calorie intake required to drive a wind powered car instead.
It might not be surprising to find that driving a wind powered car is actually better in terms of CO2 impact than riding a bike – after all wind power is zero carbon (the embedded energy in a windmill is repaid in about six months of operation – after that it’s all carbon free) – the assumption though has been that biking is zero carbon too, but it ain’t.
Biking requires 40 additional calories per mile – or 400 additional calories for a ten mile trip.
Using some typical food carbon footprints and assuming ten miles a day for a year you get a total annual impact of 333kg CO2 – from riding the bike.
This is over and above the normal food impact – which, based on a mixed diet of 2,400 calories a day (for example) would be responsible for 2 tonnes of CO2 a year – veggies and vegans will do better than that of course.
Driving a wind powered car on the other hand requires 100 calories an hour (to power the driver), which is roughly 4 calories per mile (assuming average 30 mph) this produces 76g of CO2 for a ten mile stint and a total of 28kg of CO2 for that 10 miles a day for a year.
The difference is 0.3 tonnes CO2 per year. The wind car is one third of a tonne of CO2 better than the bike…!
Like I say not surprising that wind cars win if you accept that wind power is zero carbon and biking requires more food than not biking.
But the big surprise in all of this, and perhaps the bit that makes it worth sharing – is that an electric car powered by the grid as it is, actually emits only ever so slightly more carbon a year than biking the equivalent distance.
A grid powered electric car travelling 5000 miles per MWh of electricity will produce 94g CO2 per mile (including the drivers contribution), that’s 342kg per year of CO2 for the 10 mile a day trip. Only 9kg of CO2 per year more than cycling. And what’s 9kg out of one third of a tonne?
This is counter intuitive I think.
Biking isn’t so obviously squeaky green as it’s assumed to be – it has a carbon footprint virtually equal to grid powered electric cars – that’s a shock to me. The reason for that is probably that the human body is not the most efficient user of fuel, whereas electric motors hit the high 90 percents. And even the grid manages around 50% fuel efficiency.
No embedded carbon in the car or bike (or food chain) has been taken into account here of course – just straight use of each.
It might be interesting to look at embedded levels of CO2 in cars and bikes and calculate how many years it would take for a wind powered car to……
PS – A petrol car doing the same 10 miles a day would emit over 1.2Tonnes of CO2 in a year – about four times that of the grid EV or Bike – and 45 times that of the Wind EV.