Locally-grown tomatoes frequently have higher footprints than tomatoes imported from abroad: this is one of the striking findings from a new study that looks at the lifecycle emissions of tomato farms around the world.
The new study, published in Resources, Conservation, and Recycling, tackles the big question of how to make the tomato industry more carbon-efficient—a major concern, considering that tomatoes are the most-farmed vegetable in the world, with 186.11 million metric tons produced in 2022. For context, that figure is 68% higher than the production of the world’s second most-farmed vegetable, onions.
The University of Michigan researchers first set out to quantify the carbon footprint of this ballooning industry, and then identify ways to bring it down. To achieve the first step, they went searching through the agricultural literature for life cycle analyses (LCAs) of tomato farming, studies that tally up the environmental impacts that are generated across the production process. Their analysis drew on 50 LCAs, which covered 77 tomato production systems spread across 27 countries. The researchers only counted the emissions that occurred between planting and farm gate, to keep the data uniform (some of the LCAs included emissions beyond that point while others did not.)
Their analysis showed that emissions varied enormously depending on the type of tomato farm. For tomatoes grown in open fields, which are typical in warmer regions like Southern Europe and North Africa, emissions ranged from 10 to 340 kilograms of carbon dioxide equivalent per metric ton of tomatoes, with a median of 80 kg CO2-eq/mt. That was similar to the median 83 kg CO2-eq/mt produced by covered tomato farms that lack climate controls like heating and cooling. Meanwhile, both of these paled in comparison to emissions from covered tomato farms that are climate-controlled with heating and cooling systems—more typical in regions like North and Central Europe where the plants need extra help to grow. In these cases, median emissions were 1709 CO2-eq/mt, and ranged from 1370 to a whopping 5590 kg CO2-eq/mt.
The emissions gap between farm types is so large, in fact, that some types of locally-grown tomatoes exceed the emissions footprint of imported produce, the researchers found. For this part of the study they slightly extended the parameters of the LCAs to include emissions from transport beyond the farm gate, and looked only at the European cases, which made up the majority of the 50 LCAs included in the study. This revealed that tomatoes produced locally on climate-controlled farms generated far more emissions than imported tomatoes grown on open fields or in covered but uncontrolled conditions.
For example, the literature showed that importing such tomatoes from France to Northern Spain would reduce carbon emissions by 45%, compared to Spanish tomatoes locally-grown in heated greenhouses. Another case study showed the savings could be as high as 75%, if tomatoes were instead imported to Northern Spain from Italy and elsewhere in Spain.
The reason for this large discrepancy is the huge emissions load produced by the heating and cooling requirements of climate-controlled tomato farms. Energy use on such farms drives 85% of their total emissions, the study found, a quantity so large that it even outstrips the import-associated emissions of transport by truck and train.
The researchers note that these findings may be biased by the European focus of this part of their study, as Europe is a region where transport is road- and train-focused, and also increasingly electrified. Still, the main takeaway is how comparatively high the emissions cost of climate-controlled farms can be.
It might therefore seem like a natural solution to stop farming this way. But the reality isn’t so simple, because climate-controlled farms also happen to produce extraordinarily high yields. Compared to open-field and uncontrolled farms which generated between 11 and 257 metric tons of tomato per hectare, climate-controlled farms produced between 10 and 1298 metric tons, with a median of 447 mt/ha, the researchers found.
Relying on lower-carbon energy sources like geothermal or waste heat is one way this high-yield tomato production could continue without the climate cost, the study says. In the reviewed literature, farms that transitioned to low-carbon energy to heat and cool their crops reduced emissions by between 11 and 140%. Interestingly, one of the few cases the researchers found where local climate-controlled tomatoes produced lower emissions than imports from elsewhere in Europe was in Germany, where farmers use a ‘carbon-negative energy source’ to heat and cool indoor crops, they say.
The reviewed literature also offered clues on how to bring down emissions in other farming scenarios. Changing irrigation from a drip to a seepage system, and using surface water instead of from wells can reduce greenhouse gas emissions on farms by 12% and 19% respectively, according to some studies. Precision agriculture was found to reduce emissions by between 23% and 64%.
Meanwhile mulching—something that’s universally easy to implement—was found to cut emissions by a surprising 31% in climate-uncontrolled covered tomato farms, because it increases yields per hectare.
With an industry as large and diverse as tomato farming, these kinds of tailored solutions might be exactly what’s needed to adapt it to a climate-changed world.
Zhu et. al. “Greenhouse gas emissions of tomato production and supply: A systematic review.” Resources, Conservation, and Recycling. 2025.
Image: ©Valeria Aksakova/ Freepik
