At a time of increasing alarm about climate change, there seems an unbelievable shortsightedness in allowing the farming industry to wither and die. Fifty years or so hence, when energy has become a precious commodity and we recall with horror how strawberries once came so decadently from New Zealand to fill our supermarkets, or prawns were shipped to Thailand for peeling, we will turn to the countryside that surrounds us and ask - urgently - where is the food we need? Where are the producers?

Where indeed? The final diaspora will have taken place. Today's farmers - forgotten, maligned, misunderstood and alienated - will have long ago given up in the face of hostile economic circumstances. They will have sold their land for housing, or to the monied classes to use as a playground, and moved on to jobs which at least pay the minimum wage.

Perhaps a handful will remain, and then only in arable areas, growing maize and rapeseed on a huge scale to feed the factories pro- ducing biomass fuel. Long gone, however, will be the vital meat, milk and vegetable producers, cleared from their homes by poverty, their goods undercut by cheap imports. Farmers may be incredibly conservative creatures, and in many ways their own worst enemies, but by the middle of this century they will have been sickened off the land into other walks of life.

One can predict a crisis come the twilight of globalisation, when the government of the day, always several heartbeats too late, struggles to revive the farming industry in order to feed the nation. Huge start-up grants will be given to potato growers, dairy farmers, beef and lamb producers; training schemes will sprout, teaching the young to recognise soil, or tell one end of a cow from another. There will be legislation: rehashes of the Agriculture Acts of 1947 and 1948 to guarantee prices; the Milk Marketing Board will once again become a power in the land.

Life, after all, is always cyclical; supply and demand of food being the most inescapable law even in an age transformed by technology. Is it too far-fetched to expect a phenomenon of the kind which happened in the years after 1745, when the price of cattle rose by 300%? Or how, between 1790 and 1830, wages for a skilled agricultural labourer rose by 60%, and for the unskilled by 30%?

Far-fetched possibly only in the period of time I have allowed for it to happen. Given the speed and severity of climate change, the refusal of governments all over the world to check our self-indulgent lifestyles, and the lack of resources devoted to exploring alternative energy sources, we may start to appreciate our indigenous farming capacity rather sooner than 2060. In 1995, the UK was 87% self-sufficient in products that could be grown here. Now the figure is heading fast towards 60% and agriculture, according to executive figures, is now the equivalent of only 1%-2% of the total Gross Value Added, a proxy for GDP. Scotland's breeding flock of sheep, to give but one example, has reduced by more than 700,000, or 20%, in the past seven years.

But at whatever point we wake up to the dangers implicit in those figures and stop taking farmers for granted, we will still be too late. The annual Scottish farm income estimates slipped out yesterday, largely ignored, bringing their now predictable tale of misery. (What does it say about disregard when such catastrophic statistics do not make the BBC Radio Scotland lunchtime news?) Net farm incomes, which relate to returns to farmers for their manual and managerial labour on tenant-type farms, show a fall of 27% from £13,800 in 2004/5 to £10,000 in 2005/6. Figures for the gross output from the industry show a rise of 16%, but this is skewed by a weather-related rise of 66.3% in the potato industry, not by any general boom (the previous year total income from farming fell by nearly 11%).

Let us consider the detail: fuel and oil costs to Scottish farmers have risen 12%, veterinary bills are up 6%, other farm costs up 4%. Fertilisers and lime bills are up 4%; so, too, are feedstuffs. Interest rates - and don't forget even small farms run on a £200,000 or so overdraft - are up over 4% and labour costs are up 6%.

While the value of potatoes and cereals and horticulture has risen, the asset value of livestock has fallen 15% (11% for cattle and 44% for sheep) and milk has decreased in value by 2.5%.

All this, to the average businessman or woman in the street, represents a no-brainer. Get out now, they'd say. Don't hang around. Employ your assets and your skills and your intelligence in another sector. And that's the daily dilemma for farming people up and down the land. Should they quit, or should they soldier on for another year, working 14-hour days and earning, in many cases, under £5000 per year when the national average income is more than four times that? For all its benefits - freedom, space, a good environment for children - is this life of grinding poverty worth it?

An increasing number of families realise it isn't. In the six years between 1998 and 2004, the number of farms in Scotland fell by 10%. There are now only 68,000 people employed in agriculture here, or 2.8% of the workforce (in England, the comparative figure is only 1.6%). It is incredible to think that in 1750 eight or nine in every 10 Scots lived off the land, and as recently as 150 years ago the figure was 30%. But few farmers now would want their children to carry on in the industry.

"I would be very upset if our child wanted to farm," a farmer's wife told me yesterday, one whose dairy farm has been tenanted by her family for several hundred years. "In fact, even having a second child has meant a massive sacrifice. The farm doesn't pay the minimum wage and we depend on tax credits. We sell our milk for 17.16 pence a litre and it is sold for 60p in the supermarket.

"What breaks my heart is my husband's dedication to his animals. It's ingrained in him. He knows it's not going anywhere, but he loves the life; it's in his genes. What else can he do but carry on?"

Yet even as one good man cares - for the meantime; the NFU says one-third of family dairy farms have quit in the past six years - organic milk is already being imported from Holland and France; and some French powdered milk is being used in Scottish cheese-making. The brutal contrast between the power of the market, and the frailty of the home producer, has never been more marked.

I am reminded, when I write this, of another friend, a hill farmer in one of the remotest areas, who when I visited him at Christmas showed me the mountains of records he and his wife are obliged to keep in order to qualify for their income mainstay, the single farm payment. It was shocking, farcical: page after page of minutiae - the batch number of the wormer given to the sheep dogs; the generic name of every antibiotic issued; daily stock movements from one pasture to another. And for this useless, Stalinist paper chase, and for working 365 days a year without a holiday, he received the glorious sum of £2000. Come the collapse of global food markets, it occurs to me, we might wish we had cherished these people a little more.