Whether or not you believe in global warming (as perhaps the majority do) or that mankind’s contribution to it is significant (as increasing numbers don’t, or would rather not) we will run out of fossil fuel.  When that happens, unless we find a substitute we can mine for a few more centuries, we’re going to have to learn to power and feed ourselves sustainably.

Very little of the food we eat in the West is sustainably produced, and there may already be more people than can be fed sustainably.  If the oil ran out tomorrow, most of us in the West (at least) would starve (which might cause the planet to breathe a sigh of relief but otherwise not be considered by many to be a Good Thing). And farmers would starve along with the rest of us, because they need a lot of fossil fuel to produce our food.

So can farming be made sustainable in the sense that it could manage without direct or indirect fossil fuel input?  The farms of old were, like the rest of the economy, sustainable.  They were, like the rest of the economy, far more labour intensive than today, although they probably used less energy per calorie of food produced than developed countries do today.  The large number of farm workers and draught animals would still have needed feeding, of course, but all the energy they consumed would still have originated on the farm and would still have produced a surplus.

Ultimately, all energy comes from sunlight.  Fossil fuel is simply 300 million years of sunlight locked away in the earth to be liberated by mankind in a little over 300 years. Before that, we burned wood, liberating sunlight captured over a couple of decades, and grazed horses liberating sunlight captured in the last year.  If you can  grow firewood and grass as fast as you use them, you can keep it up indefinitely – i.e. it’s sustainable.

Organic farming does not consume fossil fuel to provide fertilisers and pesticides but those organic farmers who still power their machines and generate heat from fossil fuel are no more sustainable in the long run than any other type of farming.  In that respect, sustainability is a binary proposition.

But farm machinery can be powered by oil extracted from currently growing plants and other organisms, so farming can avoid using fossil fuel – and indeed in much of the non-Western world it probably still does. Today, that requires setting aside some proportion of crop land to provide the fuel necessary to cultivate, harvest and process the remainder.  This is what the farmers of old did, and what the extremely efficient Amish farmers of today do.  The Amish, of course, use horses to power their machines, and horses also provide some of the fertiliser for the land they cultivate. But while we may not be able to afford to go back to horse-powered agriculture, we might be able to go back to plant-powered.  Using farmland to grow fuel for combustion engines threatens food supply, and there isn’t enough land in the UK to fuel all the cars, trucks, trains and aircraft the UK uses.  But just providing the fuel for farm machinery – which is what our ancestors did – is still feasible, and might enable our farmers to maintain the efficiency while dramatically improving the sustainability of what they do.

There are academic studies of this on-line, but simply put you can extract a little over 1000 litres of rape seed oil per hectare in the UK, and you need a little over 100 litres of that to drive the tractors and machinery to cultivate that hectare.   That’s the good news. The bad news is that a farmer can get 70p a litre for rape seed oil while his red fossil diesel costs him 60p.  Until that changes, it’s hard to see what else will.

As we run out of fossil fuel, of course, its price will increase, but since a growing proportion of the diesel and petrol we all buy is now (by law) biofuel – i.e. extracted from plant sources – so will the price of rape seed oil.  So long as the subsidised price of fossil fuel for agriculture remains below the market price for bio-fuel feedstock, modern farming will be as unsustainable as the rest of our economy.