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Tomatoes from warm countries are better for the environment

Tomatoes from greenhouses emit about eight times more CO2 than those that grow under the open sky. Scientists have uncovered the world’s most eaten vegetables´ climate footprint, and greenhouses are the big CO2 culprit.

By Birgitte Dalgaard, , 1/7/2021

If we want to enjoy juicy tomatoes and simultaneously maintain a good climate conscience, we must go far beyond tomatoes that are grown in greenhouses.

– When the tomato is grown in an open field, the production emits an average of 80 kg CO2 per ton. If the tomatoes are grown in a greenhouse, they emit up to 700 kg CO2 per ton. We are talking about a factor of 5-10, emphasizes Professor Gang Liu from the Department of Green Technology.

In the research project "Mapping the EU tomato supply chain from farm to fork for greenhouse gas emission mitigation strategies", Gang Liu has been involved in mapping out the tomato's supply chain and climate footprint. The researchers have uncovered the long journey of the tomato, from farm to fork:

It is the vegetable that we eat the most, and forecasts show that in the future we will eat even more processed tomatoes

Gang Liu, Professor

– When we talk about the importance of reducing agricultural emissions of greenhouse gases, we cannot avoid discussing tomatoes.

– It is the vegetable that we eat the most, and forecasts show that in the future we will eat even more processed tomatoes, for example, ketchup, tomato sauce and peeled tomatoes, says Gang Liu.

Do not eat locally

Usually, we learn that it is most climate-friendly to buy locally produced foods, but that rule is far from true when we talk about tomatoes, which requires heat to grow. If you choose your tomatoes solely from a CO 2 footprint, you must choose the tomatoes that grow outside the greenhouses.

– In general, Southern European tomato production emits less CO2 because tomatoes grow to a greater extent in open fields. In Spain, which produces the most tomatoes in Europe, 40 per cent of the tomatoes grow in greenhouses, but when growers in southern Europe use greenhouses, they also use less heat, Gang Liu points out:

It is the vegetable that we eat the most, and forecasts show that in the future we will eat even more processed tomatoes

Gang Liu, Professor

– We have a small tomato production in Denmark. We import the vast majority of tomatoes from the Netherland, Spain and Italy, and they are shipped here assumingly by truck.

– The climate benefit of buying locally and thus avoiding transport is not at all enough to offset the climate impact of greenhouses.

But Gang Liu stresses that consumers can weigh other parameters, such as the use of pesticides and confidence in producers, higher than CO2 when buying tomatoes.

Large waste of tomatoes

The researchers’ mapping out of the European tomato's CO2 footprint has resulted in several recommendations for on-farm production, the processing process, the retail stage and in the consumers' homes.

But when Gang Liu is asked to point out where the biggest CO2 savings are to be made, he points, in addition to the greenhouses, to a large amount of food waste.

In 2016, 18 million tons of tomatoes were produced in Europe, but only 11 million tons ended up being eaten.

A tomato is actually a fruit

  • Although the tomato is botanically a fruit, it is commercially categorized as a vegetable. In the case 'Nix v. Hedden', the US Supreme Court has ruled that the tomato is a vegetable. (Source: Wikipedia)
  • In 2016, Denmark imported 35,226 tons of fresh tomatoes and 48,300 tons of processed tomatoes in the form of tomato sauce, ketchup, peeled tomatoes etc.
  • We received the fresh tomatoes mainly from the Netherlands and Spain, while the processed ones came mainly from Italy and Germany.

– It is clear that when such a large food waste occurs, it makes production less efficient and it burdens the overall climate account, says Gang Liu.

While the largest amount of greenhouse gases was emitted in the production phase, the researchers' studies show that the largest waste accumulation occurs in the processing phase. 43 per cent of tomato waste occurs when the tomatoes are processed into ketchup or pasta sauce.

– The second-largest share of waste is in the consumer stage. In the store or the family home, 20 per cent of the waste occurs, says Gang Liu.

Better utilization

All forecasts show that in the future we will eat more processed and fewer fresh tomatoes, and Gang Liu, therefore, points out that the companies that process the tomatoes must become better at utilizing the whole tomato and limiting the significant waste:

– That being said, from a climate perspective, it may make sense to use processed tomato products out of the tomato’s high season. In fact, previous research shows that processed tomatoes contain more lycopene, which has a protective effect against certain cancers, than fresh tomatoes.


Photo: Unsplash


This work was funded by REFRESH (Resource Efficient Food and dRink for the Entire Supply cHain), under the Horizon 2020 Framework Programme of the European Union.

Meet the researcher

Gang Liu is a Professor at SDU Life Cycle Engineering, Department of Green Technology. Gang Liu describes himself as an enthusiastic industrial ecologist. The idea behind industrial ecology is that waste and recyclable material are used for new production in controlled networks that in principle leave a harmless ecological footprint.


Tomato production in Denmark

Out of the EU's 28 countries (including the United Kingdom), tomato production in Denmark is very small. Danish data is pooled with the smallest tomato-producing countries. The projects assess the entire value chain from farm to fork and throughout Europe, not specific cultivation of tomatoes in Denmark.

Editing was completed: 07.01.2021