As we understand more about the environmental impact of different farming systems we can say more about the carbon footprint and sustainability of the different ways in which we produce food. A number of studies have suggested that organic farming is better for wildlife, causes lower pollution from sprays, and produces less carbon dioxide and less dangerous wastes. However, the environmental impact of importing food over long distances can reduce some of these benefits. Similarly a non-organic tomato grown in the UK under glass and heated using oil could have a higher carbon footprint than a non-organic tomato grown in the sunshine in the Mediterranean.
In both cases, it is important to consider all aspects of Life Cycle Analysis (LCA) 'from seed to fork' to ensure that we are comparing like with like and seeing the full picture. These are complicated issues and more research is needed, however if you are concerned about limiting climate change and reducing your carbon footprint then buying organic food is generally a very helpful measure, particularly if it has been locally grown. While there is no UK data for the overall global warming impact of organic farming, there is now data on energy use from Defra-funded studies (Pretty et al). These show organic farming is overall more energy efficient than non-organic farming. This is mainly because it does not use nitrogen fertilisers, which are produced from petro-chemicals in an energy-intensive process. Typically organic farming is about 30% more energy efficient for producing the same quantity of food.
Overall, organic farming appears better for tackling climate change than industrial agricultural methods. As well as the lower average energy use, organic farming also avoids the very large nitrous oxide emissions from fertiliser manufacture (a powerful greenhouse gas, 300 times as warming as carbon dioxide). Additionally, organic farming builds up soil carbon, removing it from the atmosphere. The higher soil organic matter levels of organic systems also improves the adaptability of farming to climate change, meaning widespread organic farming could play an important role in reducing the impacts of climate change on society. Higher soil organic matter levels significantly improve the drainage and water retention of soil, reducing the risk of flooding and the effects of drought on food production.