Horsepower as a proxy measure for (un)sustainability

Twenty-five billion horsepower. To argue the detail would be futile. But, as a proxy for sustainability it is very useful, because it does relate to a real beast that we know and understand. A horse in good condition can produce about 14Hp in bursts and sustains slightly less than 1Hp at a good working plod. In order to do this the beast eats, drinks and excretes. A horse, compared to a car is a reasonable converter of fuel to useful energy. You may argue that the average car only runs for 20 percent of the time. Yes, and horses sleep. If you want to tinker at the edges of this vision with energy conversion factors and life-cycle analyses from manufacturing to disposal you may, but remember a horse works for about 15 years and a car for less than that. And, pace vegetarians, at the end of its life you can eat the horse. You could cut the numbers in half and the vision is still apocalyptic.

An ordinary domestic car engine produces between 80Hp and 200Hp Some produce more, like the 350Hp 6 litre V8 in a Cadillac Sliverado. Some produce less, like the 61Hp Smart car. But if you were to stick a wet finger in the wind and say the average car has about 100 horses you wouldn't be far wrong.

You see where I am going? Can you fodder 100 horses in your garden? Horses, like cars, like us consume hydrocarbons and produce energy, water and oxides of carbon (carbon monoxide and carbon dioxide).

In 2006, according to UK DfT statistics there were 27,830,000 registered cars (not taxis, not light goods, not HGVs or buses, just cars). 2,410,000 were company cars. So, call it 25 million private cars in the UK (France, Germany, Italy, the Netherlands are similar, fyi, and the USA has over 100 million).

Then, that makes 25 million cars times 100 horses each, is two and a half billion horses: just to power Britain's private car fleet, not even buses, trains, trucks, industry or heating. The fodder for those horses approximates very closely to the debt we are incurring to to the earth by driving. And, as it happens, is a reasonable way to envisage our biofuels requirements if we were to convert from petroleum. The private transport energy demand of the UK, France and the Netherlands alone would require us to grow enough to feed more horses than there are humans on the earth (six billion ish).