Local vs seasonal food: Which one is better and how to choose between them

Ingredients are affected by numerous variables; whether it’s locally produced, imported or in season, plays a huge role on the price as well as on the climate impact. But which one is better?

Local vs Seasonal, when it comes to definitions

Many associate seasonal with locally produced food, but this isn’t always true. The accepted definition of seasonal food is the following:

• Food that is produced and consumed in the same climatic zone, e.g. UK, without high energy use for climate modification such as heated glasshouses or cold storage (2). 
  
  
• Local or locally sourced food means to purchase food that is grown or harvested close to where the individual lives and is distributed over shorter distances than usually (3). There are more definitions out there when it comes to local food, however, they seem to agree on the above and differ on the actual distance in terms of production and distribution.
  
  

Worldwide Data on locally produced food 

The UK currently produces the equivalent of about 60% of domestic consumption, part of which is exported. About 54% of food on plates is produced in the UK, including the majority of grains, meat, dairy, and eggs. Domestic crops include 54% of fresh vegetables, mostly sugar beet, potatoes, and oilseeds, though only 16% of fresh fruit (4). 

In 2020, 93% of domestic consumption of fresh vegetables was fulfilled by domestic and European production, while fruit supply is more widely spread across the EU, Africa, the Americas, and the UK (5).

Overcoming natural seasonality, strategies to meet demands of out-of-season ingredients

British consumers expect year-round availability, which means that import of fruits and vegetables from warmer climates such as Italy, southern France, and Spain are essential to meeting demand for out-of-season produce. British winter crops are more limited in range, being dominated by root vegetables and leafy greens. 

In order to overcome the natural seasonality of fruit and vegetables, four strategies have been found by the industry. 

1. Protected cultivation to produce out of season (e.g. heated greenhouses).
2. Import of produce from where it is in season or can be produced in non-heated greenhouses (e.g., Spain during winter).
3. Cold storage of seasonal produce to consume it out-of season.
4. Consumption of other vegetables that are in season.
   
   

Comparison of production methods of out-of-season ingredients

Locally produced, protected cultivation: Greenhouse vs. Imported, non-local but seasonal: Open field cultivation

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 fertilizers) 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. 

This bar chart shows the explanation, including 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.

Ingredient example, the lettuce case study

Lettuce, when in season, is produced in the UK in open fields from May to October. The rest of the year lettuce could be imported from Spain where it is produced in open fields or in non-heated greenhouses. It is also produced in the UK in glass heated greenhouses (from November to April).

The carbon footprint of open field cropping in both the UK, when in season, and Spain presents similar values (Spain a little higher because of the transport to the UK): 0.33 kg CO₂e/kg of lettuce VS 0.45 kg CO₂e/kg of lettuce respectively. Nevertheless, they are comparable even if 2600km of transport by truck are included. The hotspots (i.e., the stages with the highest emissions), in both cases, are fertilizer production and application, fuel use and energy for irrigation. The carbon footprint of lettuce produced in glasshouses in the UK, thus out of season, can reach up to 3 kg CO₂e/kg of lettuce. In this case, the hotspot is, for 90%, the energy required for heating (6). 

How to choose between local vs. seasonal ingredients

Local food is not necessarily more environmentally friendly than imported, seasonality is! When a produce is in season, then it should be local! Indeed, if the produce is transported by plane, the carbon footprint of these foods, even if grown in open fields, results higher than the same food produced in glass heated greenhouses. Using local produce when in season is a good strategy to reduce your carbon footprint.

Sources 

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. Foster, C., Guében, C., Holmes, M., Wiltshire, J. and Wynn, S., 2014. The environmental effects of seasonal food purchase: a raspberry case study. Journal of cleaner production, 73, pp.269-274.
3. Better Food UK (https://betterfood.co.uk/embrace-eating-locally/#:~:text=Eating%20locally%20first%20means%20choosing,for%20what%20constitutes%20eating%20locally)
4. UK Government Food Security Report 2021 (https://www.gov.uk/government/statistics/united-kingdom-food-security-report-2021/united-kingdom-food-security-report-2021-theme-2-uk-food-supply-sources) Accessed 30/06/2022
5. Ibid. 
6. Hospido, A., Milà i Canals, L., McLaren, S., Truninger, M., Edwards-Jones, G. and Clift, R., 2009. The role of seasonality in lettuce consumption: a case study of environmental and social aspects. The International Journal of Life Cycle Assessment, 14(5), pp.381-391.