3.1 What is the food system’s contribution to the global GHG emissions total?

3.1.1 The food system contributes 20-30% of global GHG emissions.

Global perspective – food systems contribute 20-30% of GHGs.

Based on Vermeulen S.J. et al. (2012). 

 

The food system is estimated to contribute approximately 20–30% of global human-made GHGs although there is huge inherent uncertainty in these estimates.

The major impacts come from farming/agriculture and land-use change (see above), with fertilisers, pesticides, manure, farming and land-use change together contributing as much as around 24% of global GHGs. Livestock alone contribute 14.5% of human-made GHG emissions.

Stages later in the food system such as packaging, retail, transport, processing, food preparation and waste disposal combined contribute around 5-10% of global GHGs although their importance and likely impacts are set to grow.

These stages are discussed in more detail later in this chapter (Sections 3.3 and 3.4).

Within food systems, consumption patterns and production are interrelated, both impacting on one another.

3.1.2 GHG contributions from agricultural production are particularly significant.

Agriculture contributes to GHG emissions both directly (emissions from agricultural production) and indirectly (land-use change for agricultural purposes).

Main agricultural GHG emissions:

  • Carbon dioxide
    • Fossil fuels – and more importantly, land use change
    • Less potent – but lots of it
  • Methane
    • Burping cows (enteric fermentation), dung, rice paddies, waste
    • Less of it, very potent
  • Nitrous oxide
    • Soils, dung, urine
    • Less of it, extremely potent

Farm animals are the main source of agricultural emissions

Indirect emissions
50% carbon dioxide – land use change
Direct emissions
Methane, nitrous oxide and (less significantly) CO2 from burning of fossil fuels
 

For the three major greenhouse gases, direct emissions include:

  • CO₂ from fossil fuel use (e.g. agricultural machinery, fertiliser production, pesticide production, production of farm structures (e.g. polytunnels)
  • Methane from enteric fermentation from ruminant livestock such as cows and sheep, as well as from manure, from rice paddies and from decomposing organic matter (e.g. waste in landfill)
  • Nitrous oxide from soil bacteria, from legume production, from livestock manure and urine and from nitrogen fertilisers.

Indirect emissions are primarily CO₂ emissions from land-use change (such as deforestation and conversion of peatlands to create agricultural land).

Animal farming is a major cause both of direct and indirect agricultural emissions (see this chapter Section 3.3 and Chapter 8).

Global perspective – focus on agricultural GHG emissions


Smith P., et al. (2014). 
  • Agriculture and land-use change account for 24% of total anthropogenic GHG emissions.
  • While agricultural non-CO2 GHG emissions increased, net CO2 emissions fell from 1980 onwards mainly due to decreasing deforestation, and increased afforestation rates.
  • Emissions from food transport, storage, processing and waste are additional and not shown here.

The GHGs emitted from agriculture and associated land-use change shown here (around 10 gigatonnes of GHGs) account for 24% of human-made GHG emissions.

As shown in the graph, direct methane and nitrous oxide emissions constitute around half of this, and these emissions have increased in recent years.

Emissions from land-use change and forestry (mainly CO₂) approximately make up the other half. Most, although not all land use change and deforestation is driven by agricultural expansion. Agriculture is estimated to be responsible for 80% of worldwide deforestation. Land degradation (deteriorating forests and other lands, rather than actual clearing of forests) is driven more by timber extraction and logging, rather than agriculture.

The land-use change referred to here relates to actual change of use, such as deforestation for crop production or livestock grazing, rather than land and forest degradation. Although degradation is also an important source of CO₂ emissions, it is not included here as an impact within food systems.

Some of the carbon losses from deforestation have in recent years been offset by afforestation (re-foresting land), but the net contribution from agricultural land-use change is still highly significant. There are large regional differences, with afforestation more prevalent in northern regions, and deforestation more so in southern regions of Asia and South America.

Within food systems, additional contributions come from transport, storage, and food preparation/processing (See Section 3.3).

3.1.3 Post-production GHG emissions are on average lower.

Global estimates: production & post-production GHGs


Based on Vermeulen S.J., et al. (2012). 

Agricultural production (including direct emissions from agriculture, and fertilizer production, pesticide production and energy use for animal feed) contribute the great majority of food system GHG emissions.

Post-agricultural production stages (processing, refrigeration, storage, packaging, processing, retail, catering and consumers, and waste disposal) contribute much less but can be significant for some food types.

On a global scale, there is a great deal of uncertainty in measurements.

3.1.4 The UK as an example of food-related GHG emissions in developed countries.

Many countries have sought to quantify the contribution that food consumption has on overall emissions. We use the UK as an example here.

In total, the food system in the UK contributes around 19% to UK human-made GHGs, excluding emissions from land-use change (LUC) for imported goods.

If global LUC-related emissions were included (i.e. the LUC-related emissions embedded in foods imported for UK consumption), then reported food-related emissions would increase further, although estimates of by how much vary.

The second graph shows that of the 19% contribution from the UK food system, agriculture contributes around 40% of the total, again excluding land-use change. The agricultural stage is the most significant largely because of livestock which contribute methane and nitrous oxide.

Other contributions are much lower, but also of importance, such as transport, food manufacture, packaging, and storage and cooking both at home and in business (retail and catering). Developed countries tend to have higher relative impacts from later stages than less developed countries, due to more energy use in processing and storage (refrigeration).

National level studies of different stages of the food system (the UK as an example)

Adapted from: Garnett T. (2008)

Global land use change attributable to UK consumption increases the UK’s footprint further although estimates vary.