Friday, 3 August 2012

CO2 emissions from cycling

The Environmental Transport Association (ETA) Trust (always an interesting website) reports that the European Cyclists Federation (ECF) have compared the CO2 produced by cycling with other modes of transport.

According to the report cycling is responsible for CO2 emissions of 21g per km. The calculations included emissions associated with production, maintenance and fuel. The figures were based on a heavy 19kg European-style town bike built using 14.6kg of aluminium, 3.7kg of steel and 1.6kg of rubber and the cost of producing the extra calories consumed by a cyclist rather than a motorist. The report calculated that an average car produced 271g and a bus 101g.

It concludes that Europe could reduce its overall emissions by one quarter if its population cycled as regularly as the Danes. In Denmark the average person cycles almost 600 miles each year – far more than the EU average of almost 120 miles per person per year and a total of 46 miles in Britain. ETA comment that this is largely due to better facilities in Denmark, as the climate and generally flat urban areas are similar in both.

Figures like this are always fun, but a little misleading. Although it’s right to consider the embodied emissions in the bike itself, an even more favourable comparison would be to look purely at the marginal emissions for those who already own a bike (and that’s most of us) – mainly tyre wear for a bike (plus a teeny bit of oil, brake blocks and wear & tear on other components).

When I cycle to work (2.5 miles each way, not very flat) I usually reward myself with a bun or a few biscuits, but the calorific value consumed (and net carbon emissions) are lower than the marginal energy that I exert compared to the wet days when I drive. In other words I’m eating into my fat resources on cycling days, and adding to them on other days. So there’s not too many extra CO2 emissions from that. I have attempted to use a more direct carbon conversion from, say, the footprint on some packets of crisps but it’s very hard to know exactly how much energy I use cycling (and I do know I use less energy now that am I fitter than when I first started regularly cycling to the office 6 years ago).

Finally, there’s one thing to avoid – that tempting shower on arrival at the office. If heated by electricity, the emissions from an extra shower are likely to undo all the good work cycling. A 3 minute shower using an average 8.5kW (based on electric ones advertised in the UK) and Defra grid average emissions would use 0.425kWh, equivalent to about 223g of CO2 (see the NEF's Carbon Calculator for an easy converter). Longer showers - baths - only add to the net emissions.