At least 3.2 million tonnes of carbon would be taken up by soil if all the UK's farmland was converted to organic farming, the Soil Association said.

This would be the equivalent of taking nearly one million cars off the road, according to research by the organic organisation ahead of the Copenhagen COP15 Summit on climate change.

Patrick Holden, director of the Soil Association, said: "Unless we are successful in tackling climate change, we won't be able to feed the world's growing population, however we farm.

"This report shows that agriculture can reduce greenhouse gas emissions while producing food sustainably."

The UK's Climate Change Act commits the Government to delivering an 80% cut in greenhouse gases by 2050.

According to the Intergovernmental Panel on Climate Change (IPCC), 89% of agriculture's global greenhouse gas mitigation potential is from carbon sequestration - the natural removal of the gas from the atmosphere by soil and plants.

The Soil Association's Soil Carbon and Organic Farming report indicates that, on average, organic farming produces 28% higher levels of soil carbon compared to non-organic farming in Northern Europe, and 20% higher for all countries studied in Europe, North America and Australasia.

In the UK, grasslands and mixed farming systems also have a vital role to play, and soil carbon may go a long way to offsetting the methane emissions from grass-fed cattle and sheep, the report said.

The widespread adoption of organic farming practices in the UK would offset 23% of UK agricultural emissions through soil carbon sequestration alone, more than doubling the UK Government's "pathetically low" target of a 6-11% reduction by 2020, it continued.

A worldwide switch to organic farming could, it claims, therefore offset 11% of all global greenhouse gas emissions and raising soil carbon levels would also make farming worldwide more resilient to extremes of climate like droughts and floods, leading to greater food security.

Peter Melchett, policy director of the Soil Association, said: "This research underlines the immediate and profound effect that organic farming techniques could have in reducing greenhouse gas emissions in the UK and globally.

"Climate change means that business as usual in our food and farming systems is no longer an option. To minimise tropical deforestation and maximise soil carbon sequestration we need to move to healthier diets based on unprocessed, seasonal produce and grass-fed meat in moderation rather than intensive poultry and pork."

"With dietary shifts, we could feed the world sustainably, address the health and diet-related ill-health time bomb, and help meet our greenhouse gas targets."

The Soil Association was founded in 1946 by a group of farmers, scientists and nutritionists who observed a direct connection between farming practice and plant, animal, human and environmental health. More information can be found at www.soilassociation.org

To read the full and summarised findings of the Soil Association's climate report visit www.soilassociation.org/climate.aspx