you don't pay road tax !

[[XAP]Bob]

Exhaled carbon dioxide doesn't count, whether you're riding a bike or sitting in a car.

By burning fossil fuels, you are releasing the carbon captured by the trees/marine life/whatever, thousands of years ago, when the oil/coal was formed. These are the emissions that are doing the damage, as the atmosphere can't cope with all this extra carbon. Cyclists don't burn fossil fuels, so don't contribute to this problem.

Erm - I disagree.
The excess breathing I do on a bike as opposed to in a car is the emissions for that mode of transport.

Most of it is short cycle carbon, but it's still emissions - I'm not suggesting that it's a lot, but there is some emission

[Big T]

Another excuse for me not to go to the gym then.

I must produce less carbon sat at home watching the telly, than working up a sweat in the gym

[SilverBadge]

How do you manage that? Are you having your meals flown in specially?

I went to a presentation recently about lowering car CO2 emissions - one of the early stats to show how difficult reductions would be was that cycling had a CO2 cost of 34g/km (walking was even higher) compared to a current car average of ~170. I e-mailed the speaker to challenge this, as my own calculations work out as below 10 - his explanation (the figure wasn't his) was that this included the carbon cost of producing and transporting the extra food required, assuming both that (1) for the average rider cycling isn't an activity burning off existing surplus calories and (2) that if one ate extra calories they would be of "typical" carbon cost rather than e.g substituting higher calorie foods for lower calorie ones. Also left out of the equation is the realisation that (3) if vehicle efficiency improves, so will the calculated carbon cost of cycling, and (4) if fuel taxes were higher, then less travel-intensive food production techniques would be favoured, again with a reduction in calculated CO2 cost for cycling. And of course (5) a fitter person moves more economically and thus with less CO2 cost for those many non-cycling hours of their life too.

[kwackers]

I went to a presentation recently about lowering car CO2 emissions - one of the early stats to show how difficult reductions would be was that cycling had a CO2 cost of 34g/km (walking was even higher) compared to a current car average of ~170. I e-mailed the speaker to challenge this, as my own calculations work out as below 10 - his explanation (the figure wasn't his) was that this included the carbon cost of producing and transporting the extra food required, assuming both that (1) for the average rider cycling isn't an activity burning off existing surplus calories and (2) that if one ate extra calories they would be of "typical" carbon cost rather than e.g substituting higher calorie foods for lower calorie ones. Also left out of the equation is the realisation that (3) if vehicle efficiency improves, so will the calculated carbon cost of cycling, and (4) if fuel taxes were higher, then less travel-intensive food production techniques would be favoured, again with a reduction in calculated CO2 cost for cycling. And of course (5) a fitter person moves more economically and thus with less CO2 cost for those many non-cycling hours of their life too.

I've seen something similar done, in reality you make lots of assumptions about what the cyclist eats. I seem to remember it was possible to show that a cyclist used more calories than the car, which is fundamentally ludicrous; you can't realistically compare the most efficient method of transport on the planet with dragging two tonnes of metal back and forth.
Wonder how much energy is required to produce 1kg of sugar? I reckon I do about 100 miles to the bag.

[thirdcrank]

The whole exercise is futile IMO. It's virtually impossible to exist in modern society entirely on your own resources and devices, so like it or not, your own effect on the planet is really a share of the whole of society's, which you can marginally improve by being more responsible yourself.

I was in a hardware shop discussing the level of imports of things like tools. The four candles man showed me a hammer for a couple of quid, shaft made in Mexico, head in India.

The government, in all its guises, seems to be one of the most profligate. No obvious way of stopping them.

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PS I'm not suggesting that's a reason for people not to try, just saying that the effect on the future of the planet of an extra Mars Bar during the ride to work is nothing compared to cabinet ministers jetting of here there and everywhere for no other reason than looking busy, and everything else that goes with it. I'm due to get my old age pension in a few weeks and a forest has died to send me the info.