3. Food systems & greenhouse gas emissions

This chapter takes a closer look at greenhouse gas emissions arising from the food system both at a global and at a country level. It looks at emissions by life cycle stage, by food type and (briefly) by dietary pattern. 

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.

References: 

General references

3.1.1

  • See Chapter 4 for more on the options for reducing food related GHGs, and for more on land-use change and its related impacts on biodiversity
  • See Chapter 5 for more on land-use change.
  • Vermeulen, S.J., Campbell, B.M. and Ingram, J.S.I. (2012). Climate Change and Food Systems. Annual Review of Environment and Resources. 37, 195-222.

3.1.2

  • See Chapter 2 for an explanation about different greenhouse gases and their relative global warming potential.
  • See Chapter 4 for more on the options for reducing food related GHGs, and for more on land-use change and its related impacts on biodiversity.
  • Smith, P., M. Bustamante, H. Ahammad, H. Clark, H. Dong, E.A. Elsiddig, H. Haberl, R. Harper, J. House, M. Jafari, O. Masera, C. Mbow, N.H. Ravindranath, C.W. Rice, C. Robledo Abad, A. Romanovskaya, F. Sperling, and F. Tubiello. (2014). Agriculture, Forestry and Other Land Use (AFOLU). In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  • Kissinger, G., M. Herold, V. De Sy. (2012) Drivers of Deforestation and Forest Degradation: A Synthesis Report for REDD+ Policymakers. Lexeme Consulting, Vancouver, Canada.

3.1.3

3.1.4

3.2 What are the main GHG contributions to agricultural emissions?

3.2.1 Livestock is by far the main contributor of GHGs from farming.

The largest source of direct GHGs are enteric fermentation emissions from ruminants

Smith P., et al.  (2014). 

Global emissions from agriculture are mainly in the form of methane and nitrous oxide arising from ruminant enteric fermentation.

Synthetic and organic fertiliser applications (e.g. manure) are also significant contributors.

GHG contributions from livestock

 

Gerber, et al. (2013). 

Livestock contribute 14.5% of human-made GHG emissions. Of this 14.5%:

  • Enteric fermentation from ruminant animals contributes nearly 40% of livestock GHGs.
  • Emissions related to manure contribute around 25%.
  • Production of animal feed contributes around 13%.
  • Land-use change for livestock contributes nearly 10%.
  • Post-farm emissions (processing & transport from farm to retail) contributes only 2.9%.

 

 

Within the livestock sector, almost all GHG emission contributions come from enteric fermentation (methane emissions), manure (both methane and nitrous oxide), animal feed production (carbon dioxide and some methane), and from land-use change (carbon dioxide emissions from land clearing).

The percentage contribution from post-production emissions is very small for livestock – the CO₂ that is emitted results from the processing, transport of livestock products between the production and retail point as well as from cold storage.

Livestock contribute significantly to GHGs, as already discussed. But impacts of livestock are not limited only to GHGs.

Livestock & animal products: a convergence of issues

Source: FCRN. See side panel for references.

Livestock are an important driver of deforestation, and as such are implicated in biodiversity loss.

Much of the world’s grain production is to feed animals, with up to 1/3 of arable land dedicated to producing feed for animals. Since food energy is lost during the metabolic process, the use of cereals to feed animals is argued by some to be inefficient. Critics say that the land used to produce livestock feed could be better used for other purposes – such as to produce crops to be eaten by humans, or allowed to return to non-agricultural land use.

Livestock rearing also requires large volumes of water for feed production and to a lesser extent for consumption directly by animals, washing and so forth – although most of this is ‘green water’ – water that falls on grazing land or on unirrigated crops. Livestock manures are a major cause of water pollution, largely through poor manure management which pollute water systems .

Many human diseases are zoonotic in nature, meaning they care transmitted from animals to humans.

At the same time, animal products can be important sources of nutrition and livestock keeping is central to the livelihoods of some of the world’s poorest people.

3.2.2 Livestock emissions vary depending by species.

Focus on livestock – global emissions by species


Gerber, et al. (2013)

Globally, beef and dairy cattle contribute most to the GHG total from livestock, since they are ruminants and farmed in high numbers. Other ruminants (for example buffalo, sheep and goats) contribute less overall because fewer of them are reared. 

Non-ruminants such as pigs and chickens contribute less than cattle mainly because they do not emit as much methane from enteric fermentation, and their feed conversion efficiency is higher. As such GHG emissions from pork and poultry production are lower, despite their being farmed in large numbers.

3.2.3 Livestock systems can also generate benefits to the environment.

  Benefits Disbenefits Comment
Nutrition Excellent for protein, calcium, iron, vit. B12   Excessive fat; protein can be more than needed Animal foods not essential; plants can substitute
Non food benefits Leather, wool, manure, rendered products Manure can be a pollutant Quantities needed? Plant alternatives?
Substitution cost Eating will always produce an impact Generally plant foods have lower GHG profile  
Carbon storage Pasture land stores carbon – can sequester in right conditions if moving from bad to good grazing Excessive grazing & land use change releases carbon and reduces soil quality Land use change from pasture to crops will generate CO2. Huge uncertainties around the sequestration potential of grazing systems – more work needed
Resource efficiency Livestock can consume grass & byproducts (some limited by legislation) Supplemented with grains & cereals in intensive systems Byproducts can be used directly as energy source in AD systems
Geography Some land not suitable for cropping Arable land used for livestock when it could for example be allowed to re-wild. Intensified systems are arable hungry

Livestock can make positive contributions to sustainable food systems.

Animal products can supply many important nutritional benefits (see Chapter 8); livestock farming can also generate byproducts such as leather and wool; under the right conditions grazed pastures can store increased levels of carbon. Some research suggests that under the right conditions good grazing management can even lead to soil carbon sequestration, although the evidence base is uncertain and this is still a contested and under-researched issue. Animals can eat grass and byproducts not suitable for humans; and they can be produced on land not suited to crop production. Well managed livestock can also contribute to biodiversity and the aesthetic value of landscapes.

However, if livestock production continues to expand, or if livestock are poorly managed, the negatives can outweigh the positives.

High levels of meat consumption may generate health problems (see Chapter 8); mismanaged byproducts (such as manure) can be polluting; excessive or poorly managed grazing can cause land degradation and associated soil carbon loss while forest clearance to make way for grazing animals or feed crops causes CO2 release and biodiversity loss. While livestock can consume byproducts, livestock in many systems (and increasingly so) are not fed solely on grass or byproducts but on dedicated feedcrops; and 40% of arable-quality land is used for livestock.

3.2.4 Grazing livestock and soil carbon sequestration: a contested issue.

Grazing livestock and soil carbon sequestration: a contested issue

  • Advocates of grass-fed beef systems argue that well managed grazing livestock can help sequester carbon in soils
  • It is claimed that this sequestration can partly or entirely outweigh the methane and nitrous oxide the animals emit; potentially grazing livestock systems can even be ‘emission negative.

If sequestration is assumed the carbon footprint of beef can shift from very high to very low

Röös E. and Nylinder J. (2013).

 

Changes in management strategy have been argued to lead to sequestration

Graph produced from data presented in: Wang, et al (2015)

But caution is needed…

  • This is still an under researched area and the evidence base is still uncertain.
  • Important to note that the benefits of avoided methane and nitrous oxide emissions are permanent, while carbon sinks are temporary.
  • The extent to which sequestration occurs depends on: the status of the soil carbon levels before any management change, the baseline soil type and conditions, specific management techniques, climate, rainfall etc. – and many of these factors can change
  • Also need to consider: reversibility (grassland can be ploughed up) and saturation (after some decades soils approach carbon equilibrium; methane and nitrous oxide emissions will then always outweigh the sequestration); impacts on biodiversity can be mixed and may be negative
  • What is clear is that grasslands are major carbon stores – so it is important not to plough them up
  • Some grasslands are home to unique flora and fauna and grazing livestock may have historically contributed to this. But other grazing lands contain very little biodiversity.
  • Poor grazing management can contribute to soil carbon losses while grazing livestock have historically (although less so now) been an important driver of deforestation.

3.2.5 Emissions from cropping and horticultural production are on average lower than those from livestock.

Fruit & vegetables

Lower GHGs, but this depends on energy use and later stage inputs.

Air freighted
Grown with additional heating or protection
Pre-prepared, trimmed or chopped
Fragile or highly perishable
Unseasonal products (where airfreighted or grown with heated/protected environment)
Seasonal field grown, robust produce
grown without additional heating or protection
Overseas produce field grown, robust produce grown without additional heating or protection & transported short distances by sea or road
Domestic is not always better

Fruit and vegetables contribute fewer GHGs than livestock on average, measured in terms of kg CO2 eq./kg product – although other functional units may include emissions per unit of calories or protein, and the differences between products may narrow or widen.

Lower impact produce are those that are field grown (for example not grown in greenhouses), transported shorter distances by road or ship (not air) and those that are more robust – i.e. less requiring of rapid transport modes such as air and less perishable – thus less prone to being spoiled or wasted.

More emissions-intensive fruit and vegetables are typically those grown in heated greenhouses, where much higher energy inputs are required. Airfreighting is extremely GHG intensive and so any produce transported in this way has a very high carbon footprint. Highly fragile produce may be more easily spoiled and wasted, meaning a waste of embedded emissions.

3.2.6 Produce grown in heated greenhouse systems can have high emissions (UK example).

UK example – heated greenhouse impacts

UK greenhouse grown tomatoes 3x more energy intensive than Spanish field grown

But, need to consider:

  • energy use from refrigeration during transport
  • wastage during transport
  • equipment manufacture of glass green-houses vs. plastic tunnels
  • what if heating is from renewable energy?

A study by the UK Department for Environment, Food and Rural Affairs (Defra) measured the GHG emissions from heated tomato production in the UK, compared to imported field grown (non-heated) tomatoes from Spain. The UK tomatoes were found to be three times more energy intensive than Spanish, due to the fossil-fuel energy requirements of heated food production in the UK. The warmer climate in Spain meant that additional heating was not required. See Section 3.3 for more on this.

However, this was not a full study of all the impacts, including water use, while important factors such as energy use in refrigeration during transport were not included. Additionally, it is important to make sure that like-for-like product comparisons are made – for example cherry tomatoes have different production and storage requirements to standard tomatoes.

A further study (Antón et al. 2005) compared the impacts of permanent glass greenhouses in the UK with plastic (short-lived) tunnels in Spain, finding that the energy used to produce the plastic tunnels was a significant contribution to the overall impact.

The point is that heated production uses energy and has GHG emissions associated with it, but impacts from transport, material production, and storage as well as environmental issues other than GHGs need to be considered.

References: 

3.2.1

  • Smith, P., M. Bustamante, H. Ahammad, H. Clark, H. Dong, E.A. Elsiddig, H. Haberl, R. Harper, J. House, M. Jafari, O. Masera, C. Mbow, N.H. Ravindranath, C.W. Rice, C. Robledo Abad, A. Romanovskaya, F. Sperling, and F. Tubiello. (2014). Agriculture, Forestry and Other Land Use (AFOLU). In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  • Gerber, P.J., Steinfeld, H., Henderson, B., Mottet, A., Opio, C., Dijkman, J., Falcucci, A. and Tempio, G. (2013). Tackling climate change through livestock – A global assessment of emissions and mitigation opportunities. Food and Agriculture Organization of the United Nations (FAO), Rome.

Diagram references:

Further reading:

3.2.2

3.2.3

3.2.4

For an example of some of the claims made about the potential of grazing livestock to sequester carbon see:

And for some papers that adopt a positive perspective on the role of grazing ruminants in sequestering carbon see:

3.2.5

Further reading:

3.2.6

3.3 How important is transport?

3.3.1 GHG contributions from transport depend on the mode of transport.

Food Miles: Is nearer better?

​ ​

Not necessarily: depends on

Mode of transport

Efficiency of transport vehicles

The trade offs

  • e.g. energy use in storing something vs. energy in transporting it – both cold stores and transport uses energy
  • Growing in heated greenhouses can be more energy intensive than importing

But

localised food systems can have other social & environmental benefits

Globally food transport is growing

Solvability: decarbonising transport energy use may be harder to address than stationary energy use (e.g. very limited renewable alternatives to aviation fuel).

GHG impacts arising food transport are not particularly significant, although they have increased in recent years.

The mode of transport is important, with air-freight having a much higher impact (see below).

This impact cannot, however, be assessed in isolation from impacts at other stages.

There are trade-offs to consider regarding energy use for both storage and transport, because both emit GHGs. This underlines the point that the whole system needs to be considered.

There may be other social, economic and environmental benefits arising from more localised food systems.

3.3.2 Air freighting food generates high GHG impacts.

Air freighting food generates high GHG impacts


Source: Sim (2007).

Airfreighting is the most GHG-intensive mode of transport.

This study shows how the impact from long-distance transport via air as compared with other modes (in this case road), can be very high.

However a full life cycle approach needs to be taken. A comparison between roses grown in heated conditions in the Netherlands and then transported the short journey to the UK versus those grown in Kenya and airfreighted to to the UK found that the airfreighted roses had lower overall emissions. 

This is because the heating and lighting requirements to grow roses are extremely high, and therefore highly energy intensive.

3.3.3 We cannot consider “food miles” in isolation of other life cycle impacts.

Further isn’t always worse

Green = Lower in comparison
Red = Higher in comparison

GWP t CO2 eq. t-1

  UK Overseas
Tomatoes, UK vs Spain 2.2 0.7
Strawberries, UK vs Spain 1.0 0.9
Potatoes, UK vs Israel 0.3 0.5
Poultry, UK vs Brazil 2.8 2.6
Beef, UK vs Brazil 24.0 32.2
Apples, UK vs New Zealand 0.3 0.9
Lamb, UK vs New Zealand 14.1 11.6

Webb, et al. (2013)

The above table illustrates that different products have different GHGs when imported to the UK vs. produced in the UK. “Food miles” cannot reliably indicate the total GHG emissions arising from a particular food product.

Different regions and countries have better growing conditions for certain foods; this may mean that, even after transport, the total GHG emissions of imported food can be lower than home-grown food.

However assessing the sustainability of products requires a wider consideration of other environmental, social, ethical and economic factors. In short, “food miles” are not a good indicator of sustainability.

3.3.4 Seasonal food choices can make a difference.

Relative importance of transport can depend on seasons


Edwards-Jones, G., et al. (2008).
 

This study illustrates the difference in GHGs for lettuce consumed in the UK for different seasons.

In winter, lettuce grown in the UK (grown indoors with fossil-fuel based heating and lighting) has a higher GHG footprint than field-grown Spanish imported lettuce, despite the shorter transport distances for UK lettuce.

In the summer, more UK lettuce can be grown outdoors, resulting in lower comparative GHGs for UK lettuce produce.

In other words, in winter the lowest GHG option is Spanish lettuce; in summer UK field-grown lettuce has (generally) lower GHGs.

There are other important issues to consider however, such as water scarcity and pesticide use.

3.3.5 Positive developmental effects of export horticulture.

Export horticulture in low income countries can contribute positively to development

  • High-value products with modern supply chains can contribute positively to incomes and jobs in poorer countries.
  • Employment and supplier rights are important conditions of these successes and need to be present.
  • Ethical trading initiatives can contribute to positive outcomes.

Products that are air-freighted may have high relative GHGs, but they also contribute positively to economic development in less developed countries. Well-managed production with modern supply chains and strong suppler/employee rights and gender equality has been shown to positively influence welfare in these situations. Standards can be strengthened following involvement in ethical trading initiatives.

The developmental benefits of export horticulture are good example of the kind of trade-offs first mentioned in Chapter 1, where some GHG mitigation initiatives (a switch away from air transport) may potentially have negative socio-economic consequences (the loss of employment and livelihoods in less developed countries). Note that perishable products such as green beans that are commonly grown in Sub Saharan Africa for export are too perishable to be transported the longer journey by sea.

3.3.6 Transport impacts in the USA.

Transport impacts in different regions – USA as an example

Weber and Matthews (2008)

 

This USA study found transport to contribute 11% of food related GHGs. The production stage contributed 83%, although their definition includes food processing, manufacture and preparation, not just agricultural production.

Note that the 11% is similar to the figure for food transport in the UK (12%) – see earlier in this chapter.

3.3.7 Transport impacts in India.

Transport impacts in different regions – India as an example


Pathak, et al. (2010)

 

This study in India found that agricultural production accounted for 87% of food system GHGs, while transport and other stages such as processing have a very small relative impact. This reflects the fact that food systems in India tend to be more localised and less mechanised than in countries such as the US or UK. More locally produced food is consumed, so transport impacts are very low.

In general, there is a lack of research in for Asia, and it is unclear how this might change over time.

It is unclear how the relative impact of non-agricultural stages might change over time, as diets and production systems shift as a result of industrialisation and economic development.

See Chapter 4 and Chapter 7 for more on dietary changes in different regions.

References: 

General References

Further reading:

3.3.1

3.3.2

3.3.3

3.3.4

3.3.5

3.3.6

3.3.7

3.4 How important is storage and packaging?

3.4.1 Fresh vs. frozen.

Fresh vs. frozen food


Ligthart, Ansems and Jetten (2005)

 

This study finds that frozen carrots have higher impacts than fresh, due to energy use for freezing and cold storage.

Similar results are found for broccoli

But there are questions to consider:

  • To what extent does fresh produce generate greater waste than frozen?
  • If year-round fresh broccoli or carrots is obtained through imports that have energy costs, might frozen produce be better outside of the growing season?

Carrots :
Freezing food requires energy and packaging. This research showed higher GHGs for frozen, canned and packaged (laminate carton) carrots than fresh.

Broccoli:
Frozen broccoli has been shown to have higher GHGs than fresh broccoli, but the difference in GHGs depends on other factors such as food waste and transport.

If less food is wasted from frozen produce, then the difference between fresh and frozen in GHGs per consumed food may be less significant.

With regard to seasonality, eating frozen produce “out of season” that has been produced locally could offset the transport GHGs of eating fresh produce that has been transported long distances.

As always, the full life cycle of the product needs to be considered.

3.4.2 Packaged and canned food.

Canning and packaging increase GHGs due to material extraction, production and energy use. Here, all forms of packaging increased the GHG emissions associated with tuna.

Canning and packaging


Poovarodom, Ponnak and Manatphrom (2012)

However, these additional emissions also need to be compared to emissions from cold storage (freezing or refrigeration) of tuna meat, and potential product wastage of fresh tuna.

References: 

3.4.1

3.4.2

3.5 Which food products have the highest overall impacts?

3.5.1 Relative GHGs of different food products.

Relative GHGs of different food products


Ripple et al. (2014)

This study shows the difference in GHG per kg of produce from different food types.

Per kg of products, all ruminants (cattle and sheep mainly, but also goats) have higher GHGs than other foods, primarily due to methane production. These data do not take into account any assumptions about the potential for grazing livestock to contribute to soil carbon sequestration (see earlier in this chapter for more on this).

Monogastric (single stomach) livestock such as pigs and poultry have lower GHGs due in the main to the lack of methane produced by enteric fermentation and other efficiencies such as feed conversion rates.

While GHG contributions from livestock vary by type, there are very important non-GHG issues to consider when making comparisons.

Seafood GHGs can vary, but are still lower than ruminants.

Fruits, vegetables and grains have the lowest GHGs. This study focuses on protein-rich foods, but many fruits, vegetables and grains have similar GHGs to pulses shown here (unless airfreighted, grown in greenhouses etc., in which case the GHG per kg of product may be increased considerably as discussed earlier in this Chapter).

One consideration to bear in mind is how different functional units can influence relative GHGs (see Chapter 2 for more on functional units). For example, if we measure GHG emissions per 100g of protein, rather than per kg of product, then the relative difference between meats and vegetables can decrease. This is important when seeking to define what healthy and sustainable eating patterns look like (see Chapter 7 and Chapter 9 for more on this).

3.5.2 Animal products dominate contributions from western diets – the UK as an example.

WWF UK’s Livewell report in 2011 showed the relative GHGs from food, based on an average diet.

Meat and dairy contribute the most GHGs in typical western diets


Relative contribution of different food groups to diet related GHG emissions. WWF-UK (2011). Livewell Report, UK

It shows that, from a dietary perspective, meats, fish, eggs and non-dairy protein sources contributed over half of the GHGs arising from a typical British diet.

Dairy contributed the next highest (14%), and a third was GHGs from fruit and vegetables. Fruit and vegetables in general have a lower per kg GHG than animal products, but can have higher GHGs than sugary processed foods. If people consumed more fruits and vegetables, in line with health recommendations, clearly the impacts of this category would increase and other categories could decline.

3.5.3 GHG hotspots in production and supply chain vary by food type.

Emissions from agriculture dominate the carbon footprint of most foods – methane emissions from ruminants; nitrous oxide from soils; CH₄ and N₂O from manure; and CO₂ from energy use on the farm (tractor fuel and fuel for heating) and for the production of mineral fertilisers.

This is always the case for animal products but for plant based foods there are some exceptions: 

  • Transport will dominate if produce is air-freighted or when fruits and roots are transported very long distances
  • Packaging: contributes significantly to GHG emissions of bottled drinks
  • Preparation/cooking: this can be significant for lower impact foods, e.g. a baked potato
  • Storage – frozen peas, or see frozen carrots example here

These are just examples, and many of the topic areas have been discussed in more detail already. A great deal depends on the energy source that is used: for example if peas are frozen using renewable energy then the relative impact of the freezing and storage process will be lower than if fossil-fuel based energy is used. The same would apply for preparation and storage.

All the post harvest impacts very much depend on the energy source used. Using packaging as an example, the contribution of this step to a product’s carbon footprint is influenced by the recycling rate of packaging materials (for example glass bottle, jars and metal tins). Higher recycling rates would in theory reduce the relative GHG emissions for producing 1 bottle of beer for example, because the bottle would not need to be made from scratch every time, although breakage rates and the distance to the recycling plant will influence the conclusion.

References: 

3.5.1

3.5.2

  • WWF UK (2011) Livewell Report, UK.
  • The GHG emissions from different eating habits, and how this relates to health are discussed in more detail in Chapter 7 and Chapter 9.

3.6 Conclusions

  • Food systems contribute up to 30% of global GHGs.
  • Agriculture contributes the largest share of this.
  • Within agriculture, GHGs from livestock are highest; protected horticulture can also have high impacts Some methods of transport, packaging, preparation and storage also result in foods with high GHGs.
  • Our dietary patterns have a strong bearing on overall GHGs since our demand for certain types of food drives food production and associated emissions.