Cutting the emissions of twaddle

SHOULD you, an environmentally conscious citizen, walk or cycle?

Nature, you might think, refined Shank’s mare over millennia, so it must be the perfect mode of transport. Physics professor David MacKay disagrees; using our legs to push the pedals of a bike, he claims, is at least twice as efficient as pounding the ground.

In his book Sustainable Energy without the hot air, MacKay seeks to cut “emissions of twaddle”. Getting off fossil fuels is important. “We are all encouraged to make a difference but many of the things that allegedly make a difference don’t add up,” he writes. Twaddle emissions are high because people don’t look at the facts and do the sums. MacKay does both.

Walking burns fuel; tillage, harvesting and transport require energy. A kilo-Watt-hour (kWh) is the amount of heat a one-bar electric fire puts out in an hour. The pilgrim trudging to Compostella produces about 3.6kWh for every 100km travelled. A cyclist generates around 1.6kWh; the bike is the most efficient mode of land transport.

If the pilgrim travelled on a train, powered by electricity from reusable sources, the demand would also be around 1.6kWh. A high-speed one would need twice as much energy and a high-speed diesel would use 9kWh. These figures assume the trains are full and well maintained.

As a user of Dublin Bus, I was dismayed to learn that the energy demand of buses may be as high 31kWh per passenger per 100km, depending on the load etc. Buses may not be that environmentally friendly but they’re better than planes. Eco-criminals in private jets clock up a staggering 150kWh for every 100km travelled. A fully-laden Boeing 747 has an energy demand of 50kWh per passenger. Taking a long-haul trip, MacKay writes, “has an energy cost slightly higher than leaving a 1kW electric fire on, non stop, 24 hours a day all year”. Nor is there much hope that flying will be more environmentally friendly in the future. The Airbus A380 is about 12% more energy efficient than a 747 and this, MacKay thinks, is about as efficient as aircraft will ever be. Don’t be tempted to switch to the ship; an ocean liner will use around 103kWh for every passenger sailing 100km.

Transport accounts for one-third of energy consumption in Britain. Motorists there drive 686 billion passenger-kilometres each year. The typical commuter, travelling alone by car, uses 40kWh per day. Only a quarter of this energy goes to pushing the car and 1% to moving the driver. The rest is squandered in heating up the engine, the radiator and the brakes and in generating turbulence in the air. Clearly, motorists are great eco-sinners.

But these figures don’t tell the whole story. They cover only the running costs of the various technologies. Bikes, cars, planes and ships, like our own bodies, have to be built and, at the end of their lives, their remains must to be laid to rest, a process which demands further energy. In addition to the 80kWh per 100km travelled, the typical car, requires 76,000kWh to construct, or 14kWh per day over a 15-year life. In addition, 1.4 units of oil are needed to produce a unit of petrol. And then there’s the cost of providing roads.

MacKay’s brilliant and thought-provoking book, dedicated “to those who will not have the benefits of two billion years accumulated energy reserves”, examines sustainability in all its aspects; electricity generation, farming, heating and public services. Technical appendices give the calculations which support the claims made in the text; anyone with a Leaving Certificate grasp of applied maths can follow them.

The prose style is lively with a touch of wicked humour. Consumer goods, MacKay remarks, pass through three stages. When “new-born stuff is displayed in shiny packages” in a shop, it is called “goods”. Taken home and unwrapped, it becomes “clutter”. Eventually, “by a miracle of modern alchemy”, it becomes “rubbish”. However, “to the untrained eye, it can be difficult to distinguish this rubbish from the highly desirable good it used to be”.

Sustainable Energy – without hot air by David JC MacKay is published by UIT, Cambridge.