How green is my bicycle?

Like most cyclists, I suspect, I float around on my bike buoyed up by the idea that I am doing my bit to save the planet. Compared to motorists, of course, this is mostly true. Per passenger kilometre, cars put out 200-300 grammes of carbon dioxide (the chief greenhouse gas). Cyclists, meanwhile, are rated at zero - which may not be quite realistic, given that we are breathing as we ride, but our CO2 emissions are negligible.

So far so good, but what about the bikes we ride? Here the picture gets murkier. I rang Chris Juden, the Cyclists' Touring Club's technical officer and an authority in the field.

The bad news is that bikes are getting less green. The old steel frames were heavy but it was standard to get a lifetime guarantee. Today, lighter bikes have built-in obsolescence: aluminium frames fatigue, and carbon-fibre parts (such as forks) bear stickers recommending replacement after just three years.

Even maintenance has been affected by the demise of the very idea of the consumer "durable". "The cost of labour to service is higher," explains Juden, "so it's no longer worth manufacturing parts in such a way that they can be repaired." So bike bits are actually designed to be disposable.

And then there's the air (and sea and road) miles issue. Like everything else, the bike industry is global. Juden estimates that, in the sum of their parts, most modern bikes will have already travelled further on their way to the shop then they are ever likely to be pedalled. And let's not even get into labour conditions and environmental regulation in China and Vietnam.

What's the answer? Well, the nearest thing to a fair-trade, organic, ethically correct bicycle is to buy local - either a British-made brand such as Brompton, or a steel lightweight from an artisan frame-builder. Then the longer you have it and the further you go, the more marginal its original environmental cost becomes.

In other words, all you need to do is keep riding it.