The focus of public and policy debate about the climate change impact of food has mostly been on transport.  “Food miles” has become shorthand for thinking about the climate change impact of food. But food system related emissions  result not only from the transport of food. Emissions also result from the conversion of land for farming, the process of farming itself, the energy used in food processing and retail, and from food waste.

A new report from Britain titled Local food and climate change – the role of community food enterprises looks at all stages of the supply chain. Using a life cycle analysis, the report takes into account emissions impacts at all stages, from agricultural production (and its associated inputs) through to processing, packing, transport, retailing, home storage and preparation, and final disposal. Its conclusion: carefully designed local food networks can reduce greenhouse gas emissions in every part of the food chain.

Farming itself is a significant source of greenhouse gas emissions. Agriculture is a major source of methane, which is many times more powerful as a greenhouse gas than carbon dioxide (methane is 25 times more potent than CO2 over a 100 year time horizon but 72 times as potent over 20 years); and nitrous oxide, which is 296 times more powerful. The Intergovernmental Panel on Climate Change estimates that agriculture is responsible for 13.5% of emissions worldwide. If the connection between deforestation and agriculture is taken into account, farming’s contribution to causing climate change rises considerably. In Latin America, for example, about 70% of previously forested land in the Amazon is used as pasture, and feed crops cover a large part of the reminder. Deforestation is responsible for just under 18% of emissions around the world.

Greenhouse gas emissions from agriculture arise both from the process of farming itself and from the production of inputs such as fertilizers, fuel for machinery, energy for heating and materials, and animal feed. The process by which fertilizer is produced is both energy intensive (generating carbon dioxide) and results in the production of the powerful greenhouse gas nitrous oxide. Emissions arise from land use change as soils are disturbed, vegetation destroyed and forests cut down. Farming practices are closely intertwined with the use of external inputs. Conserving soil carbon through methods such as conservation agriculture, organic farming, integrated nutrient management, cover cropping, agroforestry and the use of biochar not only reduces emissions from the soil but also conserves soil nutrients and reduces the need for fertilizers.

The emissions impacts of raising livestock, both direct (livestock raised on recently converted land) and indirect (the raising of crops such as soybeans and corn for animal feed) are significant: in Britain, meat and dairy consumption is responsible for 58% of food-related emissions; and globally, livestock are estimated to account for 70% of agricultural land use (30% of the Earth’s land surface) and more than half of the greenhouse gas emissions attributable to agriculture.

In assessing emissions from the food transportation system, how close food is produced to its point of consumption proves to be far from the only factor. Route planning, loading, the timing of deliveries compared with traffic and vehicle efficiency are all factors in road freight emissions. And reducing emissions from transport is not just about reducing the distance that food travels between the supplier and the retailer – transport between the retailer and the customer is even more important. It is no use reducing emissions associated with transporting food from the farm to retail, only for the good work to be undone by longer or more frequent shopping trips by car.

Emissions reductions from more efficient transport can be undone by higher emissions from storage, packaging and processing of food products. The best way to reduce emissions from food processing is to reduce the extent to which food is processed at all. But this takes thought – if processing reduces the need for later cooking or refrigeration, or uses food that would otherwise go to waste, it is unlikely that eliminating processing in favor of fresh produce would reduce overall greenhouse gases. Refrigeration is a big culprit, contributing to climate change both because of the energy used to operate the equipment and because of the impact of refrigerant gases, which are thousands of times more potent than carbon dioxide. And the interactions among refrigeration, packaging, food transport, food product innovations and various socio-economic developments have helped create cultural norms and practices that are highly energy-dependent. For example, take out-of-season consumption of fruits and vegetables. It may be less greenhouse gas-intensive to ship fruit and vegetables from Mexico or South America during the winter than to produce them locally in heated greenhouses. Similarly, emissions associated with storing apples for many months or keeping foods frozen can more than make up for the transport emissions saved by not bringing them from around the world. People have gotten used to having most foods to be available throughout the year. Slashing emissions from our food systems requires that we once again learn to live with seasonal variations.

If greenhouse gas emissions from the food system are to be reduced significantly, we will need to change the balance of the food we eat. A lower impact diet is seasonal, largely based on food that comes from plants, and can include some meat and dairy products grown to high environmental standards. Eating less – in particular, less factory-farmed meat and poultry – would be an effective way to reduce total greenhouse gas emissions.  And, as a bonus, we would be healthier for it.