Like most city dwellers, my knowledge of farming is embarrassingly limited. But a conference on agriculture and global warming has inspired me to dig deeper (pun intended) into things rural.

The speaker who grabbed my urban-oriented attention was American-born, U.K.-based Craig Sams, co-founder of Green and Black's organic chocolate bars. His message was, well, grounding.

"When we talk about food and farming we are talking about carbon," Sams pointed out. "The process by which food is made starts with carbon dioxide and nitrogen from the atmosphere and turns it into protein, fat, and carbohydrates. Plants conjure food out of thin air with help from water and sunshine ..."

Even better: "Of all the carbon capture and storage technologies on the planet, none can ever hope to be more efficient than photosynthesis ... It's absurdly cheap and has been tested for millions of years ..."

Sadly, the brilliance of nature has been tarnished by the short-sightedness of humanity.

Sams was born on a farm in Nebraska. In the 1880s, when his great-grandfather first plowed the prairie, the topsoil was four metres deep. Now it's less than one metre and "shrinking."

Every tonne of soil that Sams' great-grandfather plowed contained about 50 per cent carbon and 5 per cent nitrogen. During erosion, that tonne reacted with oxygen in the air and produced about three tons of carbon dioxide, along with the more damaging nitrous oxide – equivalent to another 30 tonnes of carbon dioxide.

Sams said that his great-grandfather lost about four tonnes of soil per acre annually, "so over 160 acres he emitted 21,000 tonnes of carbon dioxide from our little farm. Every year."

That was in the days of horsepower. "In the 1930s, when oil sold for 10 cents a barrel and tractors began replacing horses, production went up, plows went deeper, and soil erosion went crazy." The result was the Dust Bowl.

Sams pointed out that half of the world's greenhouse gas emissions from 1850 to 1990 came from agricultural activity, but therein lies the good news.

"There are 1.5 billion hectares of arable land on the planet and if you just saved one tonne of carbon emissions per year per hectare that would give us a 1.5 billion tonnes emission reduction. If you went further and instituted practices that captured and locked carbon in the soil, then you would have another 1.5 billion tonnes reduction, giving a total of 3 billion tonnes per year of carbon reduction."

This would cover more than half of the 80 per cent emissions reductions we need to stabilize our climate, he told us.

If this principle were extended to the 9 per cent of the Earth's surface that is farmed as pasture or grazing scrubland, then we could more than double that figure – and agriculture alone could bring about all the emissions reductions we need.

"Agriculture has always been a big part of the problem. It has more potential than any other industry to be the biggest part of the solution."

Sams said that society must offer farmers price incentives to farm "not just organic, but carbon-conscious organic." They should be rewarded for removing carbon from the atmosphere by the plants they grow. If they got a good price for every tonne of carbon they sequestered, "they would see carbon as their primary product."

"We are at war with an enemy, greenhouse gas ..." Sams concluded. "We can win it and farming is our most powerful weapon."

Who would have thought that the solution to the Earth's problems lay in the earth itself? And on our plates.

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Kathleen O'Hara is a Canadian journalist currently based in London.