George Monbiot is quite right to lambast the International Energy Agency for its lack of credibility over oil reserves, and I wish him well in his fight for general awareness of our dire environmental problems (The one thing depleting faster than oil is the credibility of those measuring it, 17 November).
I am glad that, almost alone among "green" journalists, he can see that productive agriculture is the most important of all our needs. But I feel that his dislike of the diesel engine, as used in farming, is informed by a concern for the pollution caused by motor transport rather than a knowledge of how farming machinery is actually used. Like many environmentalists, he seems to be unaware of some of the realities of engineering and physics, let alone farming. What I know about tractors comes from five years' experience in and under them and other machinery at a farm in France.
Monbiot says: "There are two possible options: either the mass replacement of farm machinery or the development of new farming systems that don't need much labour or energy." This is partly true, but there is no either/or about it; both options will be needed – in fact every possible option and a few that have not even been considered yet.
He says: "There are no obvious barriers to the mass production of electric tractors and combine harvesters." But to anyone who has worked with farm machinery, especially on smaller and poorer farms, the idea of electric tractors will seem ridiculous. So far, electric traction has been developed only for transport, and most successfully in railway trains. The development of batteries and control systems has been directed at the needs of passenger cars, which do not have to pull heavy loads at low speeds for long periods.
Electric tractors do exist, but are light machines similar to ride-on lawn mowers, with power outputs of around 40kW. Typical farm tractors have outputs of 100kW-200kW, and no currently available batteries could provide anything like this amount of energy, or anything approaching the working life of a diesel engine.
The best lithium-ion electric car batteries and motors work at high voltages (500V for example). As an engineer, I would blench at the idea of maintaining a 100KW, 500V system in a damp and muddy farmyard, let alone carrying out running repairs in the middle of a 50-hectare field, in the rain.
As far as I know, electric traction for farm machines has not yet been even considered as an option. If it ever reaches the stage of production, it will be very expensive indeed – far beyond the budgets of even large farms. So the diesel tractor will be with us for some time. Luckily, farms are well situated for making biodiesel fuel, and politicians should ensure this option should be used only for agriculture, and possibly for food transport.
So please let us have a realistic debate on food production, with every available technology considered, and using accurate data from impartial sources. Let us also think of all other means to survive. But don't reject Rudolf Diesel's wonderful invention yet – we have to eat.