Emissions resulting from the many activities involved in food systems, account for a substantial portion of all human-caused greenhouse gas (GHG) emissions and, as such, contribute to climate change. A major challenge for the sustainability of food systems is, therefore to figure out how its contribution to GHGs can be reduced.
If we are to be able to address and mitigate food systems’ contributions to climate change, it is important to understand where and how the greenhouse gas emissions arise across the whole food system. Also important, is to understand how different ways of organising parts of the food system, can result in differing levels of greenhouse gas emissions.
This chapter addresses the following:
- How significant are the global food system’s greenhouse gas emissions as compared with other human caused emissions?
- Where in the food system do greenhouse gas emissions arise? And how do different parts of the food system, differ in their contribution to overall emissions?
- What foods and types of food production contribute the most to emissions from agriculture?
- How are the emissions from foods affected by the location and seasonality of production, its transport, storage and packaging?
- How do food systems contribute to emissions from land use change, such as deforestation?
- The sum of all activities that make up the global food system are estimated to contribute to some 20-30% of all human-associated greenhouse gas (GHG) emissions, but the exact numbers are highly uncertain.
- In general, most emissions from the food systems occur at the agricultural production stage (24% of human-caused emissions); emissions from all processes after food is produced add a further 5-10%.
- There are three main GHGs associated with food, each with different warming effects: carbon dioxide (CO2: weak), methane (CH4: strong), nitrous oxide (N2O: very strong). The very large amounts of CO2 released, mean that its overall impact is large, despite being a less potent greenhouse gas.
- On-farm sources of emissions are responsible for roughly half of agricultural production’s overall emissions, while the other half are caused indirectly, mostly through the release of carbon dioxide resulting from the conversion of ecosystems such as forests and wetlands, into new farmland.
- Livestock are by far the biggest contributor to food-related GHG emissions (alone, contributing 14.5% of human-caused emissions), but the exact magnitude and nature of these contributions varies substantially by animal species and location.
- In general, the foods with the highest overall GHG impacts are ruminant meat, followed by other meat (including seafood) and animal products (eggs, milk), with plant-based foods having the lowest impacts.
- While farming plant-based foods generally causes fewer GHG emissions, these can be substantially increased by the use of fossil fuel intensive processes such as long-haul flights, or being grown in heated and lit greenhouses.
- Minimising transport distance (i.e. lower food miles) does not necessarily minimise a food’s lifecycle emissions, because these reductions may be outweighed by other interrelated sources of emissions, such as the need to heat greenhouses in winter.
- Dietary patterns and people’s consumption practices– particularly the amount of animal products eaten – have a tangible impact on overall GHG emissions from the food system, by driving demand for certain foods and so methods of food production
Tara Garnet, FCRN, University of Oxford
Jess Finch, FCRN, University of Warwick;
Will Nicholson, IntoFood;
Professor Pete Smith, University of Aberdeen;
Samuel Lee-Gammage, FCRN, University of Oxford;
Marie Persson, FCRN, University of Oxford;
Professor Mike Hamm, Michigan State University;
Dr Elin Röös, Swedish Agricultural University;
Dr Peter Scarborough, University of Oxford;
Dr Tim Hess, Cranfield University;
Professor Tim Key, University of Oxford;
Professor Tim Benton, University of Leeds;
Professor David Little, University of Stirling;
Professor Peter Smith, University of Aberdeen;
Mara Galeano Carraro.
Any inaccuracies and errors, remain the responsibility of the FCRN.
The production of this chapter was enabled by funding from the following sources:
The Daniel and Nina Carasso Foundation;
The Oxford Martin Programme on the Future of Food;
The Wellcome Trust;
The Esmée Fairbairn Foundation;
Waste Resources Action Programme (WRAP);
The Sustainable Consumption Institute at Manchester University.