Global warming vs your plate

Global warming is happening; no one can deny that. Year on year weather conditions are out of control, sea levels are rising and ice sheets are melting. Food accounts for up to 35% of the world’s man-made emissions (1). It’s one of the only things that as consumers, we have control over. We can choose to eat less meat, to eat more sustainably sourced produce and support restaurants and corporations who are also reducing their emissions. 

So how does food impact global warming? 

‍The Greenhouse Gases and their impacts

Nothing is net zero, and even the most sustainable farms produce emissions. Here are the main greenhouse gases and their impacts (2): 

Carbon Dioxide (CO2): Is emitted during every activity that includes energy consumption (e.g. fuel consumption for transportation and electricity consumption for food processing and storage). Also, Carbon dioxide is indirectly being released during land use change*.

Methane (NH4): Is emitted during rice cultivation and animal farming (especially from enteric fermentation and manure management) and its climate impact is 25 times stronger than CO2.

Nitrous Oxide (N20): Is emitted during the production and application of nitrogen fertilisers and its climate impact is 298 times stronger than CO2.

*Land Use Change is any way in which humans modify the natural landscape. Some of these changes are permanent destruction, such as the change of land from forest to cropland. Other changes, such as cropland abandonment and forest restoration, may attempt to repair previous damage.

Which foods emit the most emissions?

We have ranked (3) these from the most emitting to the least. There’s no surprise that beef is top of the list. 

Beef, lamb and goat: Usually the highest emissions among all food categories due to methane emissions (animal waste and cow belching/enteric fermentation) and indirect emissions from land use change (deforestation). Around 21-35 kg CO2e/kg of meat.

Chicken and pork: Usually the second highest after beef, lamb and goat but with a significant difference from red meat (3-6 kg CO2e/kg of meat).

Dairy and milk: high emissions mostly coming from animal farming (milk and yoghurt 1-1.4 kg CO2e, cheese 2-10 kg CO2e)

Fish and seafood: The CO2e values vary a lot here. The usual suspects are feed production for farmed fish and fuel consumption for the fishing boat.

Fruits and vegetables: Usually very low CO2e, unless transported by plane. The majority of emissions comes from fertiliser application and transportation (0.05-1.3 kg CO2e)

Grains and pulses: Usually low CO2e with most emissions coming from fertilisers and fuel consumption for the threshing machine (0.3-0.9 kg CO2e)

Rice: Usually medium CO2e but higher than other grains( 2-3 kg CO2e/kg of rice). Emissions (methane) come from flooded rice fields.

Production methods 

Greenhouse vs open field

When the weather conditions don’t allow produce to grow in an open field, glass heated greenhouses are used instead. They require lower inputs (less machinery, fuel and fertilisers) with respect to the open-field operations and the yield is usually higher. However, they require the construction of glass greenhouses and they need energy in the form of heat and electricity for both construction and maintenance. Electricity and heat generally cause an increase in greenhouse gas emissions.

Local food is not necessarily more environmentally friendly than imported, seasonality is! When a produce is in season, then it should be local! For most food products, transport accounts for less than 10% of the overall carbon footprint (4) (excluding transport by plane which has a higher carbon footprint and should be avoided). This is why a tomato grown in season in Spain in an open field is more environmentally friendly than a tomato grown out of season in a greenhouse in the UK, despite the Spanish tomato having to travel to the UK. 

Here are the carbon footprints of vegetables grown in the UK in season in open fields, grown in the UK out of season in a greenhouse and grown abroad in open fields in season:

Organic vs conventional farming 

This is a very nuanced subject. In the case of animals, particularly poultry and pork, organic production performs worse on a climate level. There is more land occupation for the animals, the animals live longer, require more feed and thus produce more methane (one of the worst of the greenhouse gases). 

Another drawback of organic farming is that it has a lower product yield with respect to conventional agriculture. According to some studies, yield averages are 8 to 25% lower (5) in organic systems, and this lack of productivity can create more carbon emissions. Lower yields are due to lower fertiliser input, the possibility for crops to be attacked by pests and the competition for nutrients with weeds and grass. However, with certain crops, growing conditions and management practices of certain organic systems come closer to matching conventional yields. 

Fruit, vegetables and grains show a general trend for organic production to have a slightly lower climate impact (1-2%). This is mainly due to the lower energy required to produce synthetic fertilisers. 

In terms of the environment, organic farming doesn’t use mineral fertilisers, synthetic pesticides, animal drugs, genetic engineering and food additives that may have adverse health effects. Pests are managed naturally, crops and livestock are diversified (i.e., crop rotation), and soil is improved with compost additions and animal and green manures. 

Conventional farming is better from a climatic perspective because animals have shorter lives and are housed in partial to full confinement structures and so require less land and maintenance. The main goal is to achieve high yields and high economic inputs. Synthetic fertilisers produce less nitrous oxide than organic fertilisers. Conventional leads to environmental degradation, public health problems, loss of crop variety and genetic biodiversity, and severe impacts on ecosystem services. 

In the graph below, we see the breakdown of global land area today. Half of all habitable land is used for agriculture (6).

There is also a highly unequal distribution of land use between livestock and crops for human consumption. If we combine pastures used for grazing with land used to grow crops for animal feed, livestock accounts for 77% of global farming land. While livestock takes up most of the world’s agricultural land it only produces 18% of the world’s calories and 37% of total protein (7). Agricultural expansion results in the conversion of forests, grasslands and other carbon ‘sinks’ into cropland or pasture resulting in carbon dioxide emissions.

Conclusions

Who knew food was so complicated? There is hope however and action you can take:

- Seasonal food is key, not local food! Try to buy UK grown produce when it is in season. Outside of the seasons, then opt for seasonal country specific imported goods. 

- Organic fruit and vegetables are slightly better for the environment and the climate. 

What we really need is for agriculture to become more sustainable and to not deplete our resources. Share this article with your friends and family and spread the word! The power is in the masses to make the government realise enough is enough. 

1. Crippa, M., Solazzo, E., Guizzardi, D. et al. Food systems are responsible for a third of global anthropogenic GHG emissions. Nat Food 2, 198–209 (2021)
2. IPCC (2021). Summary for policymakers. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
3. Clune, S., Crossin, E. and Verghese, K., 2017. Systematic review of greenhouse gas emissions for different fresh food categories. Journal of Cleaner Production, 140, pp.766-783
4. Our World In Data Website (https://ourworldindata.org/food-choice-vs-eating-local) Accessed: 28/07/22
5. Reganold, J.P. and Wachter, J.M., 2016. Organic agriculture in the twenty-first century. Nature plants, 2(2), pp.1-8.
6. Ellis, E. C., Klein Goldewijk, K., Siebert, S., Lightman, D., & Ramankutty, N. (2010). Anthropogenic transformation of the biomes, 1700 to 2000. Global Ecology and Biogeography, 19(5), 589-606.
7. Poore, J., & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science, 360(6392), 987-992.

This article has been reposted from its original publication in Vegan Food & Living magazine. To read the original article click here.