Keith has just released the latest in his “what if” series of articles. I always enjoy reading them because Keith manages to always find some interesting research and presents it in such a compelling way. This time is no different.

At rest we inhale about 550ml of air, of which 115ml is oxygen. When we exhale between 3 and 5 percent of that breath – about a quarter of the oxygen – becomes carbon dioxide, about 27ml of this pernicious greenhouse gas. This means that – assuming CO2 weighs 2g/liter – the average resting human produces 170,000 liters, or 340kg carbon dioxide per year. With a moderate level of activity, we can increase this to a conservative 500kg.

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In Europe, the average automobile emits about 170 grams of CO2 for every kilometer. In the USA and Canada this is considerably higher, but let’s take the European average as a starting point. If I were to travel from A to B by car then my vehicle would emit approximately 3.4kg of carbon dioxide. If I traveled at an average of 100kph (about 60mph), then the journey would take 12 minutes, during which time I would not exert myself, and thus personally emit only 8 grams of CO2. The total for the journey would thus be 3.4kg of carbon dioxide, give or take a few grams.

If, instead, I traveled by bicycle, then I would have to exert myself. There is no way I could cycle at 100kph, but can easily reach 20kph, making my journey last 1 hour. When I cycle I breathe at between 20 and 30 breaths per minute, so let’s assume 30bpm, with no increase in oxygen intake per breath. Over that hour of cycling, a person would therefore emit only 100 grams of carbon dioxide, or just 3.4% of the carbon emitted by the combined vehicle and human. If you want to reduce your carbon dioxide emissions then travel slower.

Read the rest of this fascinating article here.

I would also like to congratulate Keith on the recent recognition he got from the United Nations Environmental Program (pdf) on his other project Green Seniors. Way to go Keith!